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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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Default Re: Spark Plug Protrusion into Head?

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?

Quote:
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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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