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Old 11-07-2019, 07:18 AM   #61
Bored&Stroked
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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).

Last edited by Bored&Stroked; 11-07-2019 at 08:10 PM.
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Old 11-07-2019, 08:23 AM   #62
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Default Re: Spark Plug Protrusion into Head?

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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Default Re: Spark Plug Protrusion into Head?

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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Default Re: Spark Plug Protrusion into Head?

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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Default Re: Spark Plug Protrusion into Head?

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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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File Type: jpg Flathead Offy Spark Plug Inserts-.750.jpg (68.4 KB, 53 views)

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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Default Re: Spark Plug Protrusion into Head?

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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"!

Last edited by GOSFAST; 11-08-2019 at 06:53 AM.
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Old 11-07-2019, 09:38 PM   #73
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Default Re: Spark Plug Protrusion into Head?

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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Last edited by tubman; 11-08-2019 at 09:28 AM.
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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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Default Re: Spark Plug Protrusion into Head?

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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Default Re: Spark Plug Protrusion into Head?

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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Default Re: Spark Plug Protrusion into Head?

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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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