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Old 11-02-2019, 11:59 AM   #1
AnthonyG
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Question Spark Plug Protrusion into Head?

Read an older thread w a lot of concern on spark plugs & aluminum heads, hereís a pic w spark plug in head from chamber side as Iíve got the right head off. For protrusion look ok? Iím using Auto lite 437 spark plugs & hereís a pic of protrusion into aluminum Offy Head.
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Old 11-02-2019, 12:38 PM   #2
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Default Re: Spark Plug Protrusion into Head?

Hi Anthony, no good, needs to be addressed?

This has been an ongoing issue with ALL the different vendors with the aluminum heads. Some call for .437" reach, others .750", we find them all over the place?

How long is that plug from the gasket surface to the very first thread??

Thanks, Gary in N.Y.

P.S. This has been an ongoing issue with many of the aftermarket alum heads! We actually make our own "spacers" (photo below) to correct the plug depths!
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Old 11-02-2019, 12:43 PM   #3
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Default Re: Spark Plug Protrusion into Head?

Another reason not to run aluminum heads.
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Old 11-02-2019, 12:58 PM   #4
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Default Re: Spark Plug Protrusion into Head?

If that plug is tight/seated, then if anything, it is too short. Your plug threads are nowhere near the full depth of the head. I like to have the bottom of the plug flush with the bottom of the plug threads - with no threads hanging out into the chamber itself.
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Old 11-02-2019, 02:04 PM   #5
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Default Re: Spark Plug Protrusion into Head?

Gary (GOFAST), not sure exactly what ur asking but here’s all the geometry. The most end feature of the plug is .308-315”to the head’s gasket surface, the same plug feature is .370-.377” to the slight recessed area of the ignition chamber it protrudes into. I count 3.5 female threads in the head to the first engagement of the plug male thread. Hope that gives u what u were asking? My question is still “is the protrusion OK”? If u see the color of the porcelain in the ignition area of the plug the color ain’t bad!? What do u think? Wasnt planning on pulling other head as the issue I thought I had w compression only effected cyl. #2. But if the Geometry is wrong & that critical on this side I will?
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Old 11-02-2019, 02:15 PM   #6
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Default Re: Spark Plug Protrusion into Head?

As reference, check out the plug fit in the third picture this thread : https://www.fordbarn.com/forum/showthread.php?t=200948. BTW, it worked out well in "real life".

(Unless you have a set of Edmunds heads, forget about the "extended tip" stuff.)
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Old 11-02-2019, 02:52 PM   #7
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Default Re: Spark Plug Protrusion into Head?

So the non extended in ur pic looks like the end of the thread on plug is flush w ignition chamber w the entire porcelain cone & ignition mech fully above the head ignition chamber. Translation mines not long enough?
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Old 11-02-2019, 03:06 PM   #8
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Default Re: Spark Plug Protrusion into Head?

The location of the plug gap looks pretty good. But that is a projected nose plug. I would go with a conventional nose plug and have the threads extend to the bottom of the head. I use n NGK BR7ES plug in Offy heads.
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Old 11-02-2019, 04:05 PM   #9
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Default Re: Spark Plug Protrusion into Head?

If your 3.5 threads short, your exactly 1/4" short of full tread engagement.

I'm not sure if Ford was first with the extend reach plugs but, the reason was to keep them clean, over a variety of conditions. The porcelain being exposed to keep deposits, burned off. Plugs will usually, first foul at the porcelain to electrode join. Deposits build in that area. FH's never came with that style plug but, can benefit from them, if they clear the valve heads.
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Old 11-02-2019, 04:23 PM   #10
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Default Re: Spark Plug Protrusion into Head?

To answer Frank, porcelain looks pretty good. 2000 + or - miles on them & their a nice toast color. I’m not sure whether 437 Autolites r extended but that what the ones shown r. Not sure the # of threads means anything as long as the arc pedipalp & ground hook r located ok. In this case as measured the arc pedestal is flush to the head chamber surface where it protrudes & the ground hook is entering approx .100” beyond the durface. There’s no indication the valves were bumping them after 2000 miles.
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Old 11-02-2019, 04:24 PM   #11
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Default Re: Spark Plug Protrusion into Head?

Quote:
Originally Posted by AnthonyG View Post
So the non extended in ur pic looks like the end of the thread on plug is flush w ignition chamber w the entire porcelain cone & ignition mech fully above the head ignition chamber. Translation mines not long enough?
Are referring to the fourth picture in my thread? Yes, I would say that your plugs are waaaay too short. The threads in the heads may fill with carbon leading to all kinds of undefined problems and you may even strip a plug hole if you're not careful. There are some good reasons the guys that engineered those heads designed them with deeper plug holes. I will have to say that just about every used aluminum head I came across back in the day had carboned-up bottom threads. I found out what plugs to use (L series) an odd way. I had a friend whose father was a rep for International Harvester and had a complete set of catalogs from all the lines he carried, (including Champion). They had a contemporary listing for Allard (who used Ford flatheads with Edelbrock heads at the time), and they listed Champion L5's as the proper plug to use. I bought a set and they fit my Edelbrock's perfectly (after cleaning out the bottom threads).

Last edited by tubman; 11-02-2019 at 05:03 PM.
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Old 11-02-2019, 04:44 PM   #12
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Default Re: Spark Plug Protrusion into Head?

Quote:
Originally Posted by AnthonyG View Post
To answer Frank, porcelain looks pretty good. 2000 + or - miles on them & their a nice toast color. Iím not sure whether 437 Autolites r extended but that what the ones shown r. Not sure the # of threads means anything as long as the arc pedipalp & ground hook r located ok. In this case as measured the arc pedestal is flush to the head chamber surface where it protrudes & the ground hook is entering approx .100Ē beyond the durface. Thereís no indication the valves were bumping them after 2000 miles.
As I said, the purpose of extend reach plugs, is to extend the life of them. It has nothing to do with the color that they burn, that a function of the A/F mixture. The extension of your plug, is similar to how far the oringinal H10 plug would be.

From your combustion chamber color, it does look like your engine is using some oil and extending them more, might make them last longer, into the future.

I would say that your heads are made for 5/8 reach plugs.
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Old 11-02-2019, 05:10 PM   #13
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Default Re: Spark Plug Protrusion into Head?

Here's a link to a set of very useful charts when it comes to spark plugs : https://www.sparkplugs.com/learning-...bering-systems.

The "L" series Champions I referred to are 1/2" reach. I believe that 5/8" reach would be too long.
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Old 11-02-2019, 05:15 PM   #14
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Default Re: Spark Plug Protrusion into Head?

Thx All, will look for 625’s I’ll pull all the 437 reach & go w 625’s
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Old 11-02-2019, 07:29 PM   #15
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Default Re: Spark Plug Protrusion into Head?

Here's what I did. Used Autolite 4092 plugs and chamfered holes on combustion side to cut out exposed threads. The heads are Offy. 400. Don't know the age of the heads as they were on the engine when I got it. I tried the Autolite 437 but, the valve hit the ground electrode. Don't know anything about the cam except that it had about .330+ lift. After doing this, plus fixing many other problems with this engine, it now runs fine.
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Old 11-02-2019, 07:39 PM   #16
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Default Re: Spark Plug Protrusion into Head?

As Tubman noted, checkout the L series Champions . . . though if it was me, I'd see if I could cross-reference them to NGK or Autolite. I'm not a big fan of Champion plugs these days - too many issues with fouling (at least for me).
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Old 11-02-2019, 09:30 PM   #17
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Default Re: Spark Plug Protrusion into Head?

An interesting fact. I bought a set of L82YC's (they fit the Edmunds heads perfectly) from a vendor in England I found on eBay who had the best price on them. Interestingly, they were made in France. They have run perfectly for a couple of years. I am not surprised that "Made in France" beats "Made in China/Mexico".
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Old 11-02-2019, 11:03 PM   #18
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I don't understand why the aftermarket doesn't move the plug to the center of the transfer area and be done with it. This has allot of benefits, besides running into the exhaust valve. Run a power tip plug shorter flame front and shorter advance . economy and more. The original position over the exhaust valve was to keep the plug clean (burn off the carbon) . But the number of flathead cylinder heads sold is avery small percentage of the bottom line/ A wedge style combustion chamber and a corisponding wedge piston could give 9/10 compression in a 239 engine tha would still run on 87 oct. I tried to have EGGe make a set for me 20 years ago, but 600 bucks for the set was way beyond my means. But a few years they showed up at Bville. Sour grapes I know. but???
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Old 11-02-2019, 11:07 PM   #19
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Default Re: Spark Plug Protrusion into Head?

Ron, Do you know of any other heads besides Edmunds that have moved the plug away from the exhaust valve?
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Old 11-03-2019, 07:24 PM   #20
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Default Re: Spark Plug Protrusion into Head?

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Ron, Do you know of any other heads besides Edmunds that have moved the plug away from the exhaust valve?
Well, I know it isn't really an answer to the question, but the Harley KR racing flatheads had the plug centered over the intake valve.

When I designed the heads for our Cadillac flathead for Bonneville, I put the plug in the same place. The idea was with the KR chamber and transfer area that I wanted the flame front to start above the intake and swirl into the chamber. I figure that since Harley did it this way (and they made 1.5 HP per cubic inch on gas), was a good thing to try.

On our blown FlatCad, we've made 650 HP on alky (no nitro). Of course we also had 20 lbs of boost.
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Old 11-04-2019, 10:06 AM   #21
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Default Re: Spark Plug Protrusion into Head?

B & S, that's an impressive engine. I had a set of Grancoe with a similar combustion chamber, However the plug was in the stock location, theu were also a pop up design , so I used a 3 3.4 stroke piston on a 4" crank. This was my Bville engine, wonder what happened to it/ Last known location was Yuba city CA/
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Old 11-04-2019, 02:25 PM   #22
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Default Re: Spark Plug Protrusion into Head?

Quote:
Originally Posted by AnthonyG View Post
Read an older thread w a lot of concern on spark plugs & aluminum heads, hereís a pic w spark plug in head from chamber side as Iíve got the right head off. For protrusion look ok? Iím using Auto lite 437 spark plugs & hereís a pic of protrusion into aluminum Offy Head.
Hi Anthony, plug lengths are really considered a "non-issue" here anymore, simply choose the plug you want to use, take the heads to a "decent" machine shop and tell him to "make it happen", this is one procedure we've been doing for years now, we check EVERY head we build with for the proper depths, every one! (See the photo below)

Quote:
Originally Posted by Ol' Ron View Post
I don't understand why the aftermarket doesn't move the plug to the center of the transfer area and be done with it. This has allot of benefits, besides running into the exhaust valve. Run a power tip plug shorter flame front and shorter advance . economy and more. The original position over the exhaust valve was to keep the plug clean (burn off the carbon) . But the number of flathead cylinder heads sold is avery small percentage of the bottom line/ A wedge style combustion chamber and a corisponding wedge piston could give 9/10 compression in a 239 engine tha would still run on 87 oct. I tried to have EGGe make a set for me 20 years ago, but 600 bucks for the set was way beyond my means. But a few years they showed up at Bville. Sour grapes I know. but???
Hi Ron, hope all's well by you, go back up here and see where we evaulated those "new" Navarro heads, those things had so many issues we wouldn't have used them if we got them for "free", back when were checking them out (if you recall the Edelbrocks were still on a nationwide back-order) I had said to my customer here (Joe V.) that I wish the Chinese would go into production for these heads! After all, not any parts in them like guides, seats, valves, etc. Not even a simple helicoil, basically a casting with some machining that just needs to hold water??

We've tried for a long time speaking to Tay (Offenhauser) and Vince to effect some changes in the Offy heads, just another dead-end. They STILL haven't gotten around to making any new castings lately! Recently offered to put 10 heads on the shelf if they had any??

Good luck getting ANYONE to make a "change", we'll more than likely never see it happen.

Thanks, Gary in N.Y.

P.S. Here's a shot taken today showing 4 different plugs, different brands and different lengths, there's not a single plug here going to work in these new Offy heads without some modification, regardless of the "flycutting" fact that you see. Hard to see but there are plugs in all 4 holes!
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Old 11-04-2019, 05:38 PM   #23
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Default Re: Spark Plug Protrusion into Head?

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Originally Posted by GOSFAST View Post
Hi Anthony, plug lengths are really considered a "non-issue" here anymore, simply choose the plug you want to use, take the heads to a "decent" machine shop and tell him to "make it happen",
If you can't find an exact fit, I would at least try to find the longest plugs that I could. Sometimes the installation may need to be modified to fit exactly, but to modify (someone earlier mentioned "chamfer") the heads to use a, say, stock H10 or equivalent would be a mistake in my book, Threads in cast iron are stronger than those in aluminum. The original designers knew this, which is why most after market aluminum heads call for deeper than stock plugs. Most used heads I see have one or several Helicoils in them. I believe this is the result of installing H10's with a breaker bar by over enthusiast amateurs. Back when I raced snowmobiles (with aluminum heads), we always used the wimpy little stock spark plug wrench to avoid stripping the plug threads.
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Old 11-04-2019, 07:58 PM   #24
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Default Re: Spark Plug Protrusion into Head?

Been looking for 14mm thread .625 reach plugs. I have only been able to find .625 reach in 12mm thread. Lots of 14mm w .750 reach. I think that will be too long & interfere w valve. I’m think I’m understanding GOFAST’s spacer now. Would be a .125 spacer ring on the spark plug thread to let the .750 reach fit at the desired protrusion of the .625 reach?
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Old 11-04-2019, 08:03 PM   #25
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Default Re: Spark Plug Protrusion into Head?

Quote:
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B & S, that's an impressive engine. I had a set of Grancoe with a similar combustion chamber, However the plug was in the stock location, theu were also a pop up design , so I used a 3 3.4 stroke piston on a 4" crank. This was my Bville engine, wonder what happened to it/ Last known location was Yuba city CA/
Thanks Ron - coming from you that makes my day!

Here is a picture of the chambers in our FlatCad head - with ceramic coatings applied:

Chambers_Coated1.jpg
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Old 11-04-2019, 09:52 PM   #26
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Default Re: Spark Plug Protrusion into Head?

"AnthonyG", what kind (brand) of heads do you have? I don't think I've ever seen any that required a 5/8" reach plug.

Last edited by tubman; 11-05-2019 at 11:35 AM.
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Old 11-05-2019, 12:54 AM   #27
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Default Re: Spark Plug Protrusion into Head?

In reviewing the spark plug links, I couldn't find a 5/8 reach plug, either. So,to get the plug to fit right, I think you should go with GOSFAST spacers, as your thinking.
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Old 11-05-2019, 08:49 AM   #28
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Default Re: Spark Plug Protrusion into Head?

Offy’s as supplied by builder w the .437 reach w extended gap anvil plugs that r 3.5 threads short of flush to the inside surface
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Old 11-05-2019, 08:52 AM   #29
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Default Re: Spark Plug Protrusion into Head?

The arc pedistal is flush to inside surface + .03 gap + thickness of anvil makes total penatration at approx .09
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Old 11-05-2019, 11:29 AM   #30
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Default Re: Spark Plug Protrusion into Head?

Given that these heads have short-reach plugs (not like the new Edelbrocks with .750 reach plugs), I like to use all the threads in the head that I can - as this helps prevent wearing out the threads and stripping them (like when your plugs are too short).

On older/vintage heads, sometimes I just go ahead and put in steel Timeserts in all 8 - to give me a lot stronger threads (in steel). This is especially true if the plug threads are worn and maybe already not in prime condition.
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Old 11-05-2019, 12:30 PM   #31
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Default Re: Spark Plug Protrusion into Head?

I think a .750 reach will work for the thread but might be too long for penetration but possibly w a non extended arc anvil it might work. I’ll bring head to the performance shop I deal w & true the fit on a few to see.
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Old 11-05-2019, 01:00 PM   #32
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I used Offy heads to make my iwn combustion chamber, they are thicker than the Edelbrock's I mill the area over the valves at a 5 deg angle towards the top of the block, and the transfer area ar an 8 deg angle towards the cylinder. Using a 14 mm powertip plug and counter boring out the unused threads. This was all done by hand, The depth of the valve relief depended on cak lift/ These were all street engines (276ci). This way I could get the most compression. At one time I took a junk head and made a different trans fer angle on the cylinders and found that a 12 deg angle was best. However there isn't enough material in the head to do this and it lowers the CR. At 8 Degs you have less material removed flow is still very good and the CR is about ad high ad=s you can get it without adding material to the sides of the transfer aera. Another thing releve the angle at the end of the transfer area as well to 69* or better, This allows the AF to flow freely into the cylinder

I now have my tongue all tangled up, so I can't see what I'm sayin. Now I'll go look for some pics
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Old 11-05-2019, 01:17 PM   #33
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Default Re: Spark Plug Protrusion into Head?

Put a NGK BPR7ES .750 reach has same extension from end of thread to full extension of anvil as the Autolite, 7/32Ē. The space to the heads gasket surface of .437 reach is .26Ē. The space to the heads gasket surface for the .750 reach is less than 1/32Ē. Pretty sure valve would smack the .750 reach.
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Last edited by AnthonyG; 11-05-2019 at 01:24 PM.
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Old 11-05-2019, 01:29 PM   #34
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Default Re: Spark Plug Protrusion into Head?

First pic in last Post is .750 reach almost no clearance 2nd pic here is .437 w .25 plus spacing.
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Old 11-05-2019, 02:19 PM   #35
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Default Re: Spark Plug Protrusion into Head?

Hi Anthony, one more time, the Offy head in the photo on the left has two .060" plug-washers installed on a .750" reach plug (shown lying on the head). Looks good to go?

The Edelbrock head in the photo on the right has no shims with the .750" reach plug, only the "thin" conventional plug gasket. But we did "chamfer" all the plug holes in these heads.

The "double" copper gaskets will pose no adverse effect in the overall picture! And it may just be your easiest way out right now??

No matter what method you choose you want the plugs as "flush" as possible to the chamber, no plug "overhang" and no overly exposed threads into the chambers. Plug threads hanging into the chambers is the worst of the two.

Thanks, Gary in N.Y.

P.S. This isn't a "new" issue for us here, it's something we've watched closely for as far back as I can recall. I firmly believe that many builders/rebuilders pay little to no attention to this issue. It is something that is extremely important, could mean the difference between "stripped" plug holes or not later!
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Old 11-05-2019, 04:04 PM   #36
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Default Re: Spark Plug Protrusion into Head?

What about NGK B6HS-7534 plugs? 1/2" reach compared to say an Autolite 216 with 7/16" reach, which Offy recomends.
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Old 11-05-2019, 04:56 PM   #37
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Default Re: Spark Plug Protrusion into Head?

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What about NGK B6HS-7534 plugs? 1/2" reach compared to say an Autolite 216 with 7/16" reach, which Offy recomends.
Just to keep the numbers straight here, we stock the 216 Autolite's, the thread length isn't .437", it actually measures .406" w/o the supplied washer and .343" with the washer in place! Obviously not counting the "tip" here.

Because of this spark plug issue with the Offy heads we try to avoid building with them when possible, but when we do we have the ability to make the necessary modification to make them work. many of our builds get new spark plug "repair-inserts" from the get-go. We know when they will be required.

Thanks, Gary in N.Y.

P.S. Anthony, the copper washers (.060") run about a 1.00/ea. With the heads in my photo we would need 16 pieces to make it happen. Before we do that when we need these heads on a build I would set them up for no washers. Not a big deal over here.
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Old 11-05-2019, 05:21 PM   #38
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Default Re: Spark Plug Protrusion into Head?

Gary I’m in Stroudsburg Pa. where r u & if I get the heads to u what’s the cost to set up in ur shop?
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Old 11-05-2019, 05:28 PM   #39
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Default Re: Spark Plug Protrusion into Head?

I run Autolite 216s in my Offenhauser 8BA type heads. I chamfered a few threads off the bottom to unshroud the plugs. I guess I did it wrong. But I haven't encountered a problem thus far and it does run really well.
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Old 11-05-2019, 05:52 PM   #40
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Default Re: Spark Plug Protrusion into Head?

Everything I remember tells me that 1/2" reach plugs are the correct fit for Offenhauser heads. Champion "L" series plugs are 1/2" reach. I have a bunch of Champion "L" series plugs and a set of never been altered/never been installed Offenhauser 8BA heads at my shop. I will go up tomorrow with my camera and screw some 1/2" reach plugs into these heads and take some pictures and get to the bottom of this.

No offense intended, but all of this talk about "chamfers" and "spacers" should not be necessary. The engineers that designed these heads were not incompetent and would not have completely screwed up the spark plug holes on an otherwise successful design. It just makes no sense at all.
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Old 11-05-2019, 06:22 PM   #41
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Default Re: Spark Plug Protrusion into Head?

Tubman, I kinda thought the same thing but being a relative novice on the inside of flatty’s & my 7/16” reach seem really short w 3.5 internal threads exposed I’m trying to learn? Even w 1/2” reach that’s only another 1/16” reach into my thread will still leave 3/16” of internal thread exposed. Interested to see what u see on ur Offy heads
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Old 11-05-2019, 07:03 PM   #42
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Default Re: Spark Plug Protrusion into Head?

Thanks Denny [tubman]. Will be anxious to see those pics. I read on the H A M B, i think about guys using NGK B6HS- 7354 1/2 ' reach in Offys & like'n them. mike
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Old 11-05-2019, 08:16 PM   #43
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Default Re: Spark Plug Protrusion into Head?

I'd run an NGK plug any time before I would a Champion . . . just sayin!
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Old 11-05-2019, 08:17 PM   #44
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Default Re: Spark Plug Protrusion into Head?

I can add this tonight, the total thickness of the threads on these particular Offy heads is .570", when you add the spark plug gasket thickness it's another .065", this gives you a grand total of .635". A plug with a .500" depth is still not really correct, it will run, it's still not the right way to do things.

You'll generally find this spark plug issue only with the Offy's?

Thanks, Gary in N.Y.

P.S. This is why I stated earlier we prefer to use the Edelbrock castings, they are set up for the .750" long reach plugs, this is how it should be on ALL aluminum castings, and they have the lengths right! Sometimes we fire-slot the spark plug holes or flycut the valve pockets but we always compensate for this machining.
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Old 11-05-2019, 08:19 PM   #45
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Default Re: Spark Plug Protrusion into Head?

Just a note - Gary is referring to NEW Edelbrock castings - none of their vintage heads had long reach plugs - so make sure you know what you're buying or using.

Truth be told, I like the cast chambers in their original designs a lot better than there new CNCd'd chambers. The new ones have a lot more room over the valves - which I don't always need or want.
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Old 11-06-2019, 12:27 PM   #46
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Default Re: Spark Plug Protrusion into Head?

Gary, not sure u can see scale but it shows 1/4” deeper than head surface to face of thread dia.
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Old 11-06-2019, 02:50 PM   #47
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Default Re: Spark Plug Protrusion into Head?

Well, wrong again. I tried some "L" series Champion 1/2" reach plugs in an unmolested Offenhauser head and it came up a full 3 threads short of filling the hole. The attached pictures show the head and the plug, both by itself and screwed into the head. The only plug I had was used, so it's kind of hard to see from the combustion chamber side, but it's definitely short.

This whole thing is staring to bring back memories of the early sixties when I drag raced a '36 Ford in "D/Altered". My buddy's dad at the time could get us any plugs we wanted (as long as they were Champions). I vaguely remember fitting various plugs into our heads until we found something where we liked the fit. I seem to remember something about a Champion "N" series which have a 13/16" reach, but that's even longer. Just for shits and giggles, and because it's so easy, I just ordered a Champion N5C from Amazon.

I cannot believe that the original engineers at Offenhauser designed a high performance head that no commercial plugs fit, but it's beginning to look that way.

I'll be looking for another set of Edmunds heads after this.
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File Type: jpg IMG_1668.jpg (34.0 KB, 36 views)
File Type: jpg IMG_1669.jpg (42.4 KB, 26 views)
File Type: jpg IMG_1672.jpg (51.4 KB, 26 views)
File Type: jpg IMG_1676.jpg (56.1 KB, 27 views)
File Type: jpg IMG_1679.jpg (52.8 KB, 33 views)

Last edited by tubman; 11-06-2019 at 03:24 PM.
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Old 11-06-2019, 04:24 PM   #48
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Default Re: Spark Plug Protrusion into Head?

Hi Dennis, thought I was about to get proved "wrong" here, like I said, it's only really an issue with the Offy heads, believe me!

While we're doing the builds here, not that often with the Offy's, we do take the time to make certain a conventional, over-the-counter, plug will fit with no effort!

If you go back and "collect" all the dimensions I posted up here you should find all are "on the money" for the most part!

On a side note with respect to Anthony's photo above it appears to me to be less than .250", maybe more like .180" or so? hard to tell from the photo.

Thanks, Gary in N.Y.

P.S. Here's a customers OEM C8CM Canadian casting we tried to repair (no luck so far) with an Autolite 216 plug, fits perfect, exactly like it should!
Attached Images
File Type: jpg Flathead C8CM Spark Plug Fit.JPG (76.2 KB, 64 views)
File Type: jpg Flathead C8CM- Autolite 216 Spark Plugs.JPG (83.6 KB, 48 views)
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Old 11-06-2019, 04:50 PM   #49
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Default Re: Spark Plug Protrusion into Head?

Aw shucks, looks just like a 216 fit to me..........maybe using Go Fast's spacers and somp'n
longer......otherwise i'll keep the 216s. cause it sure runs good.
Thanks 4 your time Denny.
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Old 11-06-2019, 05:25 PM   #50
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Default Re: Spark Plug Protrusion into Head?

Picture is tough to get clear. I’m a Tool & Die Maker Machinist, believe me it’s within .01” of .25”. The angle w the phone came distorts.
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Old 11-06-2019, 07:21 PM   #51
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Default Re: Spark Plug Protrusion into Head?

Anthony, if you're referring to my last picture, you can just barely make out the side electrode at about 10 o'clock in the plug hole.
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Old 11-06-2019, 07:34 PM   #52
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Default Re: Spark Plug Protrusion into Head?

Anthony, as a machinist, you know that where a thread extends threw something, it needs to have the edge broke, for one, to as many as two threads. 1.5 is the standard I use. Besides getting the reach sorted out, I would be sure to do that.

Those sharp, partial threads can cause pre-ignition. I'd recommend that to all, especially with cast iron heads, as the iron can stay hot longer.
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Old 11-06-2019, 07:35 PM   #53
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Default Re: Spark Plug Protrusion into Head?

Me - if I had a set of the Offy heads, I would spot-face the gasket surface down whatever is required so that I could run 1/2" reach plugs. Depending on the type of electrode, the other approach might be to put a 45 degree chamfer on the combustion chamber side - which would allow a more projected nose plug.

Lots of ways to skin this cat . . . and most of them quite doable on a good drill-press. Then just chase the threads when finished.

No biggie boys, no biggie . . . LOL
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Old 11-06-2019, 07:57 PM   #54
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Default Re: Spark Plug Protrusion into Head?

Everything you are saying is true, Dale, But I am still troubled by the fact that the original designers at Offenhauser would design a high performance head that had no matching plug available. There has to be a solution out there.
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Old 11-06-2019, 08:13 PM   #55
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Everything you are saying is true, Dale, But I am still troubled by the fact that the original designers at Offenhauser would design a high performance head that had no matching plug available. There has to be a solution out there.
If they designed it for a 5/8" reach plug . . . I've never seen or used anything like that (but I've never ran Offy heads). The best situation is to set it up for 3/4" reach plugs - then you have a world of options. Obviously this requires mods to the heads, or something like Gary has done (thick washers).
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Old 11-06-2019, 08:21 PM   #56
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No wonder these have been sitting on a shelf in my shop for the last 25 years!
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Old 11-06-2019, 08:39 PM   #57
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Everything you are saying is true, Dale, But I am still troubled by the fact that the original designers at Offenhauser would design a high performance head that had no matching plug available. There has to be a solution out there.
It comes down to the same reason that those "new" Navarro heads we checked out recently got "shot-down", by us anyway, some of the mfr's just don't care! It's sad but true.

With just about any of the heads that have been mentioned here the issues are 100% fixable if you know what you're doing, there's not one issue here that could't be made to work. With the cost of those Navarro's in the 900.00 area it probably would have taken the same amount of money to fix EVERY issue we found??

This is just my take on the subject, but we find it all to often lately that this is now almost the "norm", it was very different years ago when many took great pride in their products, it has all but disappeared in today's marketplace for the most part!

Thanks, Gary in N.Y.

P.S. In my own opinion here to do a really "nice" 100% fix in this spark plug area I would most likely NOT be machining the spark plug lands any deeper to accept a shorter plug, to the contrary, I'd most likely do a modification to get the .750" long plugs to go. Again, not that big of a deal (for a decent shop anyway), I would also like to see threaded inserts in place for the plugs. On the short plug aluminum heads this would part of my modification. They would end up having .750" plugs when finished!
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Old 11-06-2019, 08:56 PM   #58
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Default Re: Spark Plug Protrusion into Head?

Tubman, no I tried to take a picture w s scale next to plug threads showing the 3/4” reach mounted in mine. Fully inserted the thread face protrudes .25” past the inside surface. Bad pic but it’s post #46
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Old 11-06-2019, 09:23 PM   #59
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Default Re: Spark Plug Protrusion into Head?

Gary , does the fire slot make any difference on a road engine? is it worth doing.
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Old 11-07-2019, 12:19 AM   #60
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Default Re: Spark Plug Protrusion into Head?

Those are a nice set of heads, but the plug would be better off in the center of the transfer area, This would provide a much shorter flame front and with a powertip plug stay nice and clean.
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Old 11-07-2019, 07:18 AM   #61
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Default Re: Spark Plug Protrusion into Head?

If the Offy's were mine, I'd probably make steel inserts for 3/4" plugs (threaded on the outside 5/8" long) - with 3/4" reach 14mm threads on the inside. I'd modify the heads to bore/tap the original threads such that I could screw in the inserts - screw them in with loctite. I wouldn't worry about stripping the short aluminum threads ever again.

But, I wouldn't do this at all - when I can order other heads that work out of the box - that already use 3/4" plugs (Edelbrock).

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Old 11-07-2019, 08:23 AM   #62
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When engine procured I was s total novice on all things Early Ford Flathead, did research on builders, chose one who had reputable standing, Jerry Livingston United Engine Specialists, spent considerable $ & received 8BA w Offy Heads & Intake. Hind sight is always 20/20
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Old 11-07-2019, 08:59 AM   #63
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Default Re: Spark Plug Protrusion into Head?

I see a Champion spark plug that has a 14mm thread 5/8Ē reach on Summit Racing site. Posted as Racing Spark plug but looks midrange for Heat, thoughts? https://www.summitracing.com/parts/cpn-1001/
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Old 11-07-2019, 10:00 AM   #64
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Default Re: Spark Plug Protrusion into Head?

That corresponds to a heat range in NGK of 9 - which is what we use for blown alky and high boost (racing only). I would think it would be very cold for your purposes - and obviously quite expensive. That is the problem with this 5/8" reach - just not many options.
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Old 11-07-2019, 10:28 AM   #65
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Thx Bored&Stroked, I’ll go w ur experience, it looked a little colder than mid range but thought I’d ask.
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Old 11-07-2019, 10:34 AM   #66
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Mike Davision did in his heads, I used them on the Hydro engine. Also Kong heads had them at the top of the head between the valves. Not the best place. The combustion process starts at the plug, and travels outward toward the farthest part of the chamber. AS this takes place pressure is built up in the cylinder pushing the piston down, However, as the pressure builds, it can reach a point where the unburnt Fuel mixture will detonate. This id the Knock we call spark knock. Now all combustion chambers have an octaine number like gasoline. THe factory will let you know what quality gas you need to use in your engine.
If in your flathead engine you have a tight piston to head clearance verylittle Af will be over the piston when the spark occurs, and it will be traveling at a high rate of speed toward the transfer area. Bringing the plug into the chamber we burn more of the AF before etion cah occurs by shorting the flame front, especially with a power tip plug. This improves fuel economy as well as increasing power from a lower grade of gas.

Back in the 29's an englishman wrote a "white paper" on combustion chamber design and created the term "Octane". I forget his name, but his work started the evolution of combustion chambers we have today.

Now I have to fix all the red lines under my misspelled words. Eye sight is getting worse.
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Old 11-07-2019, 11:27 AM   #67
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Default Re: Spark Plug Protrusion into Head?

A picture of what I described in post 15.
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Old 11-07-2019, 11:54 AM   #68
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Default Re: Spark Plug Protrusion into Head?

Ron, it was Sir Harry Ricardo. I can read what you wrote just fine.

I'll also second what you say about relocated extended tip plugs; my current '51 with a 255 Merc with carefully prepared Edmunds heads seems to have better "seat of the pants" performance than my old '36 coupe with a 276' Merc that I just bolted a set of Offenhausers on to without giving it a second thought. Now that I mention it, that car had an MSD ignition on it the produced quite a hot spark. I ran surface gap plugs in it (from an outboard motor) which sat flush with the surface of the combustion chamber, and it ran great and didn't foul. I had forgotten that until you jogged my memory.
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Old 11-07-2019, 12:43 PM   #69
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I see a Champion spark plug that has a 14mm thread 5/8” reach on Summit Racing site. Posted as Racing Spark plug but looks midrange for Heat, thoughts? https://www.summitracing.com/parts/cpn-1001/
Hi Anthony, set them up now so you won't need any "special" plugs, it may all come back to bite you at a later time?

The most probable way we would end up "fixing" these Offy's we have here on the shelf would be by welding up the existing plug registers and simply machine them to the correct heights for the .750" plugs, due in part to the head material (aluminum) I would NOT use any "short" reach plugs in these casting as long as I have the ability to make them right!

We would only have to weld on the tops where the plug gasket sits, leaving the existing threads at the bottoms of the holes. Flip the heads, back-drill thru those existing threads and tap a new hole AND new threads through the welded section!


P.S. In the event this entire procedure didn't work 100% we would still have the option at this point to install 8 new threaded inserts. The photo below here shows the type of inserts we would use! If these were for my own unit here I would do the inserts without a doubt! Weld, drill, and tap only would keep the costs in line, the inserts, obviously better, would raise the cost some!
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Last edited by GOSFAST; 11-07-2019 at 05:56 PM. Reason: C
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Old 11-07-2019, 03:20 PM   #70
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Default Re: Spark Plug Protrusion into Head?

This conversation has been very enlightening! P I’m pretty sure it’s convinced me as Bored&Stroked statement indicates, too much to do when I can put some lipstick on these pigs then sell the Offy heads & look for some Edelbrock’s!
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Old 11-07-2019, 08:15 PM   #71
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This conversation has been very enlightening! P Iím pretty sure itís convinced me as Bored&Stroked statement indicates, too much to do when I can put some lipstick on these pigs then sell the Offy heads & look for some Edelbrockís!
Yep . . . unless your last name is Offenhauser and they have sentimental value, why put 100's of dollars of time and energy into them . . . spend it someplace else of value!
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Old 11-07-2019, 08:53 PM   #72
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Default Re: Spark Plug Protrusion into Head?

While I agree about not spending a bunch of money on any heads to make things right you really need to keep things in perspective?

Just for arguments sake, if you were to spend as much as $400.00 in a decent set of heads you already own and this amount brings them up to par you would still be way ahead of the game than spending $800.00 (give or take some) for new castings. There's no guarantee's you'd still be trouble-free with new.

Thanks, Gary in N.Y.

P.S. For example, one could by those "new" Navarro's for $900.00 or so and end up worse yet? You just never know and it's tough lately cutting through all the "hype"!

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Old 11-07-2019, 09:38 PM   #73
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I've used Edmond heads on several of my builds. unfortunately they have a very small combustion chamber ofer the valves to give hi compression on the 239 block. True 8:1 CR milling the eads for .045" piston to head clearance and a power tip plug will make these small engines run quite well
As for the ignition systems, A high output coil isn't necessary. Considering the fact that we never exceed 9:1 a stock 12v ignition is all you need for complete combustion. However, when the spark occurs is important. I was afraid to cut the heads for the L-100 lift and used the Max #1, which also keeps low end torque. If your interested in a very good street engine a 259 with Edmonds head and Max #1, is one of them
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Old 11-07-2019, 09:44 PM   #74
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Default Re: Spark Plug Protrusion into Head?

DING, DING, DING. We have a winner here! I received my Champion N5C spark plug from Amazon today, took it up to my shop, screwed it into my original Offenhauser head, and it fits perfectly. The champion documentation says that the "N" series plugs have a 13/16" reach. which seems way to much, but as I said above, it fit perfectly. I didn't have my good camera with me today, so I had to take this picture with my old "Flip-Fone", but I think it shows the perfect fit.

I knew my old memories would be worth something! So you guys can forget milling machines, spacers, chamfering tools and all of that kind of stuff. Just get some Champion "N" series plugs (or their equivalents; there are a lot out there) and just screw them in.
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Old 11-08-2019, 04:46 AM   #75
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Default Re: Spark Plug Protrusion into Head?

Tubs, would it be worth "claying" that plug on an engine to check for clearance to the valve?

I guess it would be a good idea when trying any plugs that protrude past the head surface.

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Old 11-08-2019, 08:45 AM   #76
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Good job tubman! Looks good in tubman’s pic. Is this the item# & plug on Amazon. https://www.amazon.com/dp/B000CSNO44..._g8wXDbAYCK036
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Old 11-08-2019, 08:57 AM   #77
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That's the one. I looked at some cross-reference charts, and there are a lot of interchanges for those who don't like Champions. I like to use Champions as an example because I understand their numbering system.
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Old 11-08-2019, 09:03 AM   #78
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Tubs, would it be worth "claying" that plug on an engine to check for clearance to the valve?

I guess it would be a good idea when trying any plugs that protrude past the head surface.

Mart.
I really don't have anything set up at the present time, so that's probably not in the cards. I do have several stock cylinder heads with H10's installed, so I'll give them a look and maybe take some pictures. IIRC, the stockers stick out just about the same amount. Since I am not into wild cams, that's good enough for me.

One should probably do this kind of checking when installing any non-stock setup.
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Old 11-08-2019, 09:05 AM   #79
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Default Re: Spark Plug Protrusion into Head?

Good job Tubman . . . good that we have an option for the Offy heads . . . with a good long reach that is needed. Way to go . . .

I'd use an NGK B6ES if it were mine . . .
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Old 11-08-2019, 09:32 AM   #80
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Default Re: Spark Plug Protrusion into Head?

Just a heads-up, but to the best of my knowledge and as far back as I can recall all the "N" series Champions were 750" reach.

Believe I ran that series in my 13:1 468" years ago!

Thanks, Gary in N.Y.

P.S. Simple to find out, give a call out to federal-Mogul with the part number, they'll give you all the particulars. You can reach them at: (800) 325-8886, I spoke to Eric already this morning to confirm!
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Old 11-08-2019, 11:22 AM   #81
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Default Re: Spark Plug Protrusion into Head?

According to Champion, they are 13/16" reach, but they fit fine. After looking at the charts, I'll admit those numbers are confusing. I'll go with "hands-on" experience every time on this old stuff. Someone posted earlier in this thread than Offenhauser recommends "L" series plugs for their heads, which is obviously wrong. If you don't believe me, spend the $4.20 with Amazon and check for yourself. It beats "calling Eric".
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Old 11-08-2019, 11:33 AM   #82
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Default Re: Spark Plug Protrusion into Head?

As they say, a picture is worth a 1000 words.
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Old 11-08-2019, 12:04 PM   #83
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Default Re: Spark Plug Protrusion into Head?

Quote:
Originally Posted by GOSFAST View Post
Just a heads-up, but to the best of my knowledge and as far back as I can recall all the "N" series Champions were 750" reach.

Believe I ran that series in my 13:1 468" years ago!

Thanks, Gary in N.Y.

P.S. Simple to find out, give a call out to federal-Mogul with the part number, they'll give you all the particulars. You can reach them at: (800) 325-8886, I spoke to Eric already this morning to confirm!
According to the NGK cross reference - it is a .750 reach plug. Hmmmmm, the plot thickens!
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Old 11-08-2019, 12:19 PM   #84
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Default Re: Spark Plug Protrusion into Head?

That plug is the number I used in my drag car (G.M. aluminum heads), it is a reasonably "cold" plug, worked well with the 13:1 C.R.

Here's a "cut & paste" from O'Reilly Auto parts:

https://www.oreillyauto.com/
Copper Plus
Champion Copper Plus Spark Plug

(Quote)Part #120 (N5C)

Line:CHP

Check Vehicle Fit
Details
Product Information

Warranty: 1 Year Limited Warranty
Unit of Measure: Each
UPC: # 37551000869
Material Grade: Copper
Hex Size (in): 13/16 Inch
Hex Size (mm): 20mm
Thread Size: 14mm
Center Electrode Design: Standard
Thread Reach (in): 0.75 Inch
Thread Reach (mm): 19mm (.749")
Number Of Ground Electrodes: 1
Preset Gap (in): 0.023 To 0.028 Inch
Preset Gap (mm): 0.58mm To 0.71mm
Short Style Spark Plug: No
Resistor Plug: No
Ground Electrode Tip Material: Nickel-Copper Alloy
Heat Range: 5
Center Electrode Core Material: Nickel-Copper Alloy
Seat: Gasket
Ribbed Core Nose: No (End quote)

(Add) Eric was correct, after all F-M makes these Champion plugs!

Thanks, Gary in N.Y.

P.S. I believe the "13/16" being mentioned above is most like the wrench size, just a hunch here though??
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Old 11-08-2019, 01:07 PM   #85
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Default Re: Spark Plug Protrusion into Head?

I got 8 coming in a couple. I’ll let all know, looks good in tubman’s pic! Great thing about Amazon as a Prime member u can return no cost��
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Old 11-08-2019, 03:42 PM   #86
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Default Re: Spark Plug Protrusion into Head?

O K, i gotta get back in here after look'n at some older posts where several guys are runnung 216 & 437 Autolites, NGK BL6's & 4's and non of them indicated any problems with pre-ign. spark knock, heating issues etc.and seem quite happy with performance.
I'm just not so concerned now...???
I sure do admire & appreciate you fella's with so much experience & knowlege though. Thanks 4 keeping guys like me advised. mike
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Old 11-08-2019, 09:44 PM   #87
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Default Re: Spark Plug Protrusion into Head?

"AnthonyG" (and "Mart") - I am not in a position to do some actual clearance testing with these plugs. I did however take a picture of a set of "N" series plug in my unmolested Offenhauser heads as well as a regular plug in an 8BA iron head. As you can see, it looks like the stock setup is a bit more recessed than the modified setup. Given this, I would follow "Mart"'s advice and clay this set up upon assembly. I don't think there would be a problem, but you can never be sure. I hope everything works out.

"AnthonyG" - I am glad that you brought this up, as it appears to have been a continuing problem through the years. I have been reconstructing in my mind what I went through. I think I came to the right conclusion in 1961 after trying many different types of Champion plugs and seemed to have forgotten it by 1994 when I used the outboard motor "surface gap" plugs (although they worked fine). Please get back to us after you get the engine together and running so we can determine the definitive answer to what plugs to run in Offenhauser heads (it seems that Offenhauser doesn't have a clue). I don't know that the heat range (the "5" in "N5") is correct; I just used it because it is in the middle of the heat range. Also, while I believe the right size plug is mandatory, the brand is not, so you may want to try some others. In addition, from Gary's "GOSFAST" comments, I think that some plugs said to be compatible aren't.

Good luck and keep us informed.

(I have included a couple of other pictures because the difference between the "L" series and "N" series is remarkable.)
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File Type: jpg IMG_1681.jpg (64.5 KB, 57 views)
File Type: jpg IMG_1684.jpg (65.6 KB, 49 views)
File Type: jpg IMG_1685.jpg (39.1 KB, 49 views)

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Old 11-09-2019, 01:10 AM   #88
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Default Re: Spark Plug Protrusion into Head?

How about this scenario: reach of plug without gasket (total shank length)=13/16". Reach of plug with gasket installed=3/4" (assuming gasket is 1/16" thick). Anyway, the end result is what's important, and it looks like Tubman has it figured out!
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Old 11-09-2019, 08:58 AM   #89
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Default Re: Spark Plug Protrusion into Head?

With a high-lift cam, wonder if the valves will hit the spark plug ground strap? Sure looks like it. I would test fit on an engine where you know the exhaust valve is at full lift. Make sure you do it on the side where the valve is higher from the deck.

FYI: Given the valve angles/heights are different side to side, there was a time when Edelbrock actually made a left and right head - the cast chambers were different side to side. I bet the new NC machined ones are non side-specific.
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Old 11-09-2019, 10:26 AM   #90
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Got it tubman & Thx again 4 the great work!
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Old 11-13-2019, 04:36 PM   #91
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Default Re: Spark Plug Protrusion into Head?

Obviously my Offy heads depth of thread different than tubmanís. The Champion N5Cís R indeed 3/4 reach and extend into the head chamber almost 4 full threads. Oh well there going back to Amazon & guessing Iíll pull the other head & just Chamfer for the Autolite 437ís
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Old 11-13-2019, 05:21 PM   #92
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Default Re: Spark Plug Protrusion into Head?

Boy, that's strange! I wonder if someone has modified your heads or they are from different production periods. Mine came straight from Speedway in the late '90's and have been sitting on the shelf ever since because of my involvement with the Edmunds heads, and I know they haven't been messed with.

Anthony, would it be possible to get a close up photo of the top of the spark plug hole? Except for the carbon, the bottom looks just like mine.
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Old 11-13-2019, 05:39 PM   #93
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Default Re: Spark Plug Protrusion into Head?

Heads donít show any evidence of additional machining on either side of spark plug threaded holes. Light spot-faces on outside of head where plugs wire connect end is. No chamfer or counter bore on inside, threads enter as-cast chamber area. Guess it could be a different model design? I had an 8BA built by Jerry Livingston, owner of United Engine Specialists in Wichita Ka. Only marking on the head is the Offenhauser cast in & a 400 stamped on top side near temp gauge threaded hole see in pic.
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Old 11-13-2019, 06:38 PM   #94
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Not sure why but canít get photos to load for some reason? Sorry? As I said though the view from the top shows spot-faces on each to same depth clean machining the casting. Most casting removed is shy of 1/16Ē the rest r about 1/32Ē. Iíll try to load photos again later.
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Old 11-14-2019, 09:58 AM   #95
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Default Re: Spark Plug Protrusion into Head?

Anthony, Going on the assumption (which may not be correct) that your heads were modified to fit some particular type of spark plug in the past, I think it may be more productive to try to figure out what that plug was than to further modify your heads. Any modification would probably reduce the number of threads holding the plug, which is not a good thing with aluminum heads. In one of my posts I posted a link to a site that has the parameters for most brands of plugs, including reach. I think that some time going through those tables to see if there is something out there that may fit the heads as they are now would be more productive than cutting the heads again.

Here is that link again : https://www.sparkplugs.com/learning-...bering-systems.

I find the Champion table to be the most comprehensive and usually use it. If you find what you want, but don't like Champions, you can always find another brand that will cross-reference to the Champion plug.

Last edited by tubman; 11-14-2019 at 10:03 AM.
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Old 11-14-2019, 10:12 AM   #96
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Default Re: Spark Plug Protrusion into Head?

Thx tubman, I have the site & will check again. Really not being stubborn but as a retired Tool & Die Guy I can tell the heads not modified! U previously indicated it may be a different model # & that may be it. Thx & I’m working on figuring out how to reduce the file size on Pics so I can post.
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Old 11-14-2019, 10:23 AM   #97
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Default Re: Spark Plug Protrusion into Head?

Pic of top of head
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Old 11-14-2019, 10:47 AM   #98
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Default Re: Spark Plug Protrusion into Head?

From the picture, it sure looks like the heads weren't modified. On the plug hole on the right, you can see the complete set of threads. I'll try to take a picture of my head from the same angle and see if I can get a comparable view. BTW, my heads are stamped "425". As I said, my heads were procured from Speedway in the late nineties; do you have any idea of the age of your heads?
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Old 11-14-2019, 11:01 AM   #99
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Default Re: Spark Plug Protrusion into Head?

Hard to say age on mine, as said procured engine w heads on. United Engines Specialists has a Flathead only dept so assuming they have heads they’ve bought in bulk on the shelf who knows how old. I’d think ur’s marked 425 indicate sequentially a more recent run? Scale the reach on the N5C’s u have. If they’re actually 3/4” as spec indicates it’s the reason they’re not fitting mine. Calculating mine require 5/8” reach which Don’t seem to exist?
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Old 11-14-2019, 01:23 PM   #100
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Default Re: Spark Plug Protrusion into Head?

The 425 refers to the relative depth of the cylinder head. The larger number can take a higher lift cam.
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Old 11-14-2019, 02:56 PM   #101
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Default Re: Spark Plug Protrusion into Head?

OK, one more time, below here is a shot of heads I have here for another "pending" build, customer still up in the air!

These are a set of Offy "400's", still brand new, circa 1996/1997, these came straight from Tay & Vince out at Offenhauser, no "midde-man"!

I placed a better photo below showing a conventional .437" short-reach plug (Autolite 216's) in the head on the right and a conventional .750" long-reach (Autolite 3924) in the head on the left.

The "protusion" on the .750" reach is fairly obvious, same for the "lack-of-protusion" on the 216's, neither fits as-is, period.

Like I stated earlier in my post here we've been down this road many times, it isn't new here! This is why we made our own "spacers" for the correct fit (seen in post #2 above), preferably using the .750" reach pieces!

Thanks, Gary in N.Y.

P.S. You need to look closely but it is an issue that need to be addressed BEFORE installing any brand of heads! So far the Edelbrocks are the best to build on in my opinion?
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Old 11-14-2019, 02:59 PM   #102
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Default Re: Spark Plug Protrusion into Head?

Do the 400 cambered shallower 425 deeper. As pics of both heads show as cast chambers where the plug enters & machined over pistons they’re different casting design. tubman’s works w the 3/4” reach mine requires what calculates to 5/8” reach or a bit less.
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Old 11-14-2019, 03:11 PM   #103
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Default Re: Spark Plug Protrusion into Head?

I have a question Anthony, is there a reason you don't want to use the spacers? Seems like the best solution.
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Old 11-14-2019, 03:58 PM   #104
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Default Re: Spark Plug Protrusion into Head?

Gary indicate 2 spacers will do it, thats only .120" @ .060" each. I am 3.5 threads short as it appears Gary's most recent pic of a 3/4" reach is too. 2-14mm threads r .07" 1.5-14mm threads r .06" per thread X 3.5, that's.21- .24 so would take 4 spacers. too many surfaces to seat for good compression. I know Gary showed a head with a 3/4"reach w 2 spacers flush on an Offy head he has. Math don' work on mine. If as post 99 or 100 says there is a difference between my 400 stamped head and tubmans 425 head I think my casting config is different.
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Old 11-14-2019, 05:30 PM   #105
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Default Re: Spark Plug Protrusion into Head?

I just tried the Champion N5C in a new set of Offy heads and they required .200 spacer to get the base of the plug flush with the cylinder head. With .120, they hit the plug electrode. Same with the NGK BR7ES.
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Old 11-14-2019, 05:46 PM   #106
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Default Re: Spark Plug Protrusion into Head?

Is it feasible to make a set of custom spacers the height required? I would want to try and use a common sparkplug depth so that it would be fairly easy to replace down the road.
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Old 11-14-2019, 07:24 PM   #107
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Default Re: Spark Plug Protrusion into Head?

Agreed, & wish I had a lathe, if I did I’d have never started the thread & just made the right size spacers. Drill press is all I have room for. I think I saw 1/2” reach plugs, 1/2” thread depth engagement is more than adequate & chamfer .12”-.15 deep should do it. I’ll check & go minimum on the depth.
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Old 11-14-2019, 08:57 PM   #108
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That's where you need a friend with a shop! I have one of the little hobby lathes I like to play around with for small stuff, works good.
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Old 11-14-2019, 09:33 PM   #109
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Default Re: Spark Plug Protrusion into Head?

I’ve always wanted a multi machine since retiring. Hopefully someday before I’m senile
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Old 11-15-2019, 04:48 AM   #110
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Default Re: Spark Plug Protrusion into Head?

Quote:
Originally Posted by JSeery View Post
That's where you need a friend with a shop! I have one of the little hobby lathes I like to play around with for small stuff, works good.
I have one of these imported "mini-lathes". Mine has a 7" swing and can handle objects up to 14" long.Of course, it has it's shortcomings but it got me "over the hump" of being able to do a lot of things. I had looked at used "regular" lathes, but their size, weight, three phase power requirement made them impractical for my needs. One of these units would be perfect for a project like these spark plug spacers.
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Old 11-15-2019, 11:05 AM   #111
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Default Re: Spark Plug Protrusion into Head?

Tubman, do me a favor if u would, can u do an actual measurement on the reach without the compression washer on ur N5C. I just noticed thereís a sticker on the ones I got indicating for small engines? Wondering if they r the same as the one u got!
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Old 11-15-2019, 11:37 AM   #112
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Will do.
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Old 11-15-2019, 12:20 PM   #113
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Default Re: Spark Plug Protrusion into Head?

I measure .710 to the end of the threads and .750 to the end of the plug cylinder. According to NGK literature, reach is defined as the length of the threads. Is this an industry standard? I also understand that a 1 piece spacer is ideal, but is there a problem with stacking them to the desired height?

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Old 11-15-2019, 02:42 PM   #114
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Default Re: Spark Plug Protrusion into Head?

Thx flatjack9, I’d still like a measurement from the ones tubman got as it seems there’s a couple of PN#’s listed, one for small engine & one for cars.
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Old 11-15-2019, 03:01 PM   #115
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Default Re: Spark Plug Protrusion into Head?

The number equivalent to N5C on the box is 120.
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Old 11-16-2019, 08:36 AM   #116
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Default Re: Spark Plug Protrusion into Head?

Rational for having tubman physically measure the Reach on his N5C is, I went back on Amazon & found there r two N5Cís listed. One is a PN#120 for small engines, the other is a PN#A-N5C. Amazon took the N5C PN# 120 small engine plugs back no charge.
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Old 11-16-2019, 12:02 PM   #117
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Default Re: Spark Plug Protrusion into Head?

Anthony, if you can't or won't solve your plug issue with the washers then you'll need "spacers/bushings", these are machined as a 1-piece item. We've done this with a number of customers including a few members up here!

They can be machined (as mentioned above, I think a few times) to any required lengths to make up the needed "thickness", been doing this for years now! It is a bit more expensive than the washer deal but it is what it is so to speak!

Thanks, Gary in N.Y.

P.S. Here's a shot of the "bushing" sitting on a plug, the one pictured is ready to be finish-machined for the needed heights.
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Old 11-17-2019, 10:07 AM   #118
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Default Re: Spark Plug Protrusion into Head?

After all the back and forth on this, I decided that there must be something else going on. At Anthony's request, I went to my shop yesterday and spent some time looking more carefully at all aspects of this. It has become apparent that I am responsible for some misinformation here, and I want to correct the situation.

I made a bunch of measurements that Anthony requested and I think I found the problem. My N5C measures just under .750" from the bottom of the main plug body to the bottom of the minor plug body (the part with the threads). I then measured from the bottom of the washer to the bottom of the minor plug body and got .663". I then measured the depths of the holes in the head. I measured a couple of times just to be sure, and got between .540" and .580" for the 4 plug holes (yes, there was that much variation). Given these figures, my plug should have protruded about .100" from the bottom of the head. But it doesn't. With 20 lbs torque on the plug, the bottom is just about even with the bottom surface of the head. I tried up to 40 lbs, but it was still the same. This was quite puzzling to me, so just for the heck of it, I tried to thread the plug up from the inside of the head. I tried all four holes and try as I might, I couldn't get a plug started from the bottom. This leads me to the inescapable conclusion that the heads are not tapped all the way through and the N-series plugs are bottoming out on the threads in the head. I do not have a 14 mm tap, but I do have a quality "K-D Tools" spark plug thread chaser. I could not force the thread chaser all the way through the heads, even though I applied what I considered to be reasonable force. t appears that the N5 plugs are bottoming out on the threads in my never used heads and are sealing that way, and not with the normal gasket surface.

I'll bet that was what was happening back when I was racing as well. Since we never ran the engine for any extended periods of time, I don't think I ever even knew this problem existed. Who knows? Maybe a set of N5's would work well in an engine with my new heads, but it wouldn't be right.

So bottom line, the N5's are not the answer and we are back where we started from. I am very sorry that I have mislead everyone, but I guess this is the kind of the thing that can happen when you get casually involved in a thread and don't fully research the problem.

The bottom line is that I still believe that it would be better to have plugs that fit the heads properly, but it looks like that just isn't the case here. I guess spacers may be necessary.
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Old 11-17-2019, 10:44 AM   #119
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Default Re: Spark Plug Protrusion into Head?

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After all the back and forth on this, I decided that there must be something else going on. At Anthony's request, I went to my shop yesterday and spent some time looking more carefully at all aspects of this. It has become apparent that I am responsible for some misinformation here, and I want to correct the situation.
Nice writeup Tubman! Lot of information there.
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Old 11-17-2019, 11:34 AM   #120
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Default Re: Spark Plug Protrusion into Head?

I ran into the same thing Tubman did. That's why I posted #15 & #67 on this thread.
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Old 11-17-2019, 11:51 AM   #121
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Default Re: Spark Plug Protrusion into Head?

Thx for all the work on this tubman! Much appreciated!
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Old 11-17-2019, 12:31 PM   #122
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Default Re: Spark Plug Protrusion into Head?

On a set of Offy heads I used spacers with the N5C plug measuring a total of .210 consisting of spacers and a second spark plug gasket.
as noted by Tubman, plug depths will vary from cylinder to cylinder. Quality control is not the best.
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Old 11-17-2019, 12:34 PM   #123
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Default Re: Spark Plug Protrusion into Head?

Ya' know, after thinking this over, the "N" series Champions (or equivalent) may just be the correct plugs for these. Add and extra plug washer, and everything should fall into place, eliminating the need for spacers, etc. Don't really know if it's the optimum solution, but that's the first thing I'll try when I use these heads. I do know I want all of the threads engaged that I can with aluminum heads.
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Old 11-17-2019, 02:10 PM   #124
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Default Re: Spark Plug Protrusion into Head?

An extra plug washer won't be near enough. Read above.
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Old 11-17-2019, 02:51 PM   #125
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Default Re: Spark Plug Protrusion into Head?

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An extra plug washer won't be near enough. Read above.
"Nailed" that one Jack, probably need a "hundred" or so! Don't have the time to figure the exact number out??

Thanks, Gary in N.Y.

P.S. I would think after 120+ replies and over 3200 views some sort of decision would have been made at this point??
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Old 11-17-2019, 05:08 PM   #126
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Default Re: Spark Plug Protrusion into Head?

I've made my decision to use spacers and one extra plug washer totaling .210. Makes for a good fit.
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Old 11-18-2019, 12:13 PM   #127
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Default Re: Spark Plug Protrusion into Head?

I had a friend make copper spacers for the 3/4” reach plugs. .19” thick plus the existing compression gasket works on mine. Used Autolite A3924 Spark Plugs dimensions for ref. Which r recommended for the Edelbrock heads. Reinstalling head & think all will work ok. Fingers crossed
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Old 11-18-2019, 04:51 PM   #128
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Default Re: Spark Plug Protrusion into Head?

You will have no issues . . . should be a good solution
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Old 11-20-2019, 03:13 PM   #129
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Default Re: Spark Plug Protrusion into Head?

Thought Iíd show what the spark plug w .19Ē spacer plus supplied compression washer looked like installed in head. I like it. Thx all for good discussion & all the knowledge!
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File Type: jpg 681BC607-D16E-4CEB-9FCF-9B89E2782779.jpg (38.7 KB, 40 views)
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Old 11-20-2019, 05:41 PM   #130
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Default Re: Spark Plug Protrusion into Head?

Threads look great - just make sure that 'extended tip' doesn't hit the valve. I don't tend to run extended tip plugs (due to very high valve lifts) - just something for you to check!

On the other hand, if you're going to rev the heck out of it and don't have a tach - then run extended reach plugs. When you FLOAT the valves, they'll hit the plugs and close the gaps, which acts like a 'mechanical rev limiter' . . . ask me how I know these things! LOL
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Old 11-20-2019, 06:19 PM   #131
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Default Re: Spark Plug Protrusion into Head?

Lol, got Bored&Stroked, should have added the plug is not the ones I’ll be using, just a 14mm 3/4 reach I had measured for depth of thread. I’ll be using the recommended Autolite 3924 used in the Edelbrock 8BA heads
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Old 11-20-2019, 10:51 PM   #132
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Default Re: Spark Plug Protrusion into Head?

All good my friend . . . I think you are on a solid tract . . .
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