The Ford Barn

qmdv · 11-26-2018, 03:46 PM

Are there any problems using 216 plugs with the Offy heads due to the fact that where the plugs thread in there are way more threads in the head than on the plug.

51 MERC-CT · 11-26-2018, 04:02 PM

Read somewhere that excess thread exposure can cause hot spots and detonation and also in the case of aluminum heads even melting and erosion.

GOSFAST · 11-26-2018, 04:12 PM

Quote:

Originally Posted by qmdv

Are there any problems using 216 plugs with the Offy heads due to the fact that where the plugs thread in there are way more threads in the head than on the plug.

Hi "gm", would be best served having a machine shop correct this issue!

It is an area often overlooked buy many not aware of exactly how the spark plugs should fit!

If the plugs are "short" as in your case I would spotface the plug register down enough to have the threaded section of the plug and the head at the same height. The spark plug gasket needs to be configured here also.

Occasionally in this scenario (plugs too short) we've also "fire-slotted" some heads to eliminate a few threads (photo below)! This option is a bit more expensive, we leave it up to the customer!

We fix these all the time, and the Offenhauser heads seem to be worst offender??

Thanks, Gary in N.Y.

P.s. You really don't want carbon build-up on the threads in the head and you definitely don't want any "extra" (steel) spark plug threads hanging inside the chambers, this is just giving an area for "detonation" to occur.

Mart · 11-26-2018, 04:49 PM

I run 216 plugs in my 8BA style Offenhauser heads. I used a countersink to take the last couple of threads out from the combustion chamber side of the head. I never thought of trying to lower the spotface, I wouldn't have had the tools to do it anyway. I was able to countersink them in a drill press using the stop to make sure they all went to the same depth.

Mart.

qmdv · 11-26-2018, 05:13 PM

So has anybody used a longer plug

tubman · 11-26-2018, 05:15 PM

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Stock Fords used 3/8" reach plugs. A lot of aftermarket aluminum heads seem to be designed to use 7/16" reach or even 1/2" reach plugs. This has always made sense to me, as aluminum is not quite as strong as cast iron, and the extra threads would add more holding power. Why anyone would want to go against this always amazes me. There are many spark plugs that will fit these heads perfectly. I first found this out in the early '60's when I had a "D-altered" coupe powered by a flathead. It had a set of Offenhauser heads on a '42 Merc engine. I screwed a set of stock plugs into the heads (when the were off the engine,) and saw that they were about 1/8" short. A friend of mine's father was a rep for Champion spark plugs and had all of the books and specifications for the entire line of plugs. We found that Champion specified "L" series plugs for Allards (which came with Ford flathead engines and Offenhauser heads at that time). I got a set and they fit perfectly.

I think the engineers that designed the aftermarket heads knew what they were doing (if not, why buy their heads?), so we would be better off making the plugs fit the heads, not vice-versa. It's easy enough to screw a plug into an uninstalled head and see if it sits flush or not. Modifying a set of heads so as to be able to use the same spark plugs as a stocker seems like a real "rookie" move to me.

qmdv · 11-26-2018, 05:38 PM

The Autolite 216 has a 7/16 reach. The Autolite 4634 has a 1/2 reach

flatjack9 · 11-26-2018, 08:14 PM

Get a spark plug catalog. Pick the one that fits best. Why modify the heads?

4dFord/SC · 11-26-2018, 09:58 PM

I use Autolite 437 plugs in my Offenhauser heads.

qmdv · 11-26-2018, 10:25 PM

Quote:

Originally Posted by 4dFord/SC

I use Autolite 437 plugs in my Offenhauser heads.

Same reach as a 216

quickchange34 · 11-26-2018, 10:27 PM

If using those heads try NKG B5ES They have a 3/4 reach .

GOSFAST · 11-27-2018, 09:23 AM

The Offenhauser heads had/have the wrong amount of threads (length) in most of their castings, this isn't new and it also isn't correct.

The entire length is about .600", this is not acceptable for either a .375", 437", or .750" length plug. This issue SHOULD be addressed during the heads install!

Spoke to Tay (Offenhauser) himself many years ago and this is just the way it is and has remained!

The quickest "at-home" fix is use a .750" reach gasketed plug along with some dedicated spark plug shims to get the correct installed height!

We recently made some aluminum 1-pc shims (.125"/added photo below) of our our own to use instead of the single shims, works well but is a bit more expensive.

Thanks, Gary in N.Y.

P.S. Here's a shot of the .750" long plugs with some shims. The plug on the left has no shims, the one on the right has 2 (.060") shims installed. This installed height is now good. The shims are also pictured lying on the head.

tubman · 11-27-2018, 10:59 AM

"GOSFAST' - Very interesting. I did not know this as I have no experience with later Offenhauser heads. All I do know is that the vast majority of used heads I have gone through over the last 65 years either had carboned-up threads caused by running stock plugs or were crudely modified to allow the spark plug to be unshrouded. The former can be corrected, the latter usually not.

11-26-2018, 03:46 PM	#1
qmdv Senior Member Join Date: Dec 2012 Location: Payette, ID Posts: 946	Offenhauser heads with Auto Lite 216 plugs Are there any problems using 216 plugs with the Offy heads due to the fact that where the plugs thread in there are way more threads in the head than on the plug.

11-26-2018, 04:02 PM	#2
51 MERC-CT Senior Member Join Date: May 2010 Location: East Hartford, Ct Posts: 5,898	Re: Offenhauser heads with Auto Lite 216 plugs Read somewhere that excess thread exposure can cause hot spots and detonation and also in the case of aluminum heads even melting and erosion. __________________ DON'T RECALL DOING SOMETHING FOR MYSELF BASED ON SOMEONE ELSE'S LIKES OR DISLIKES

11-26-2018, 04:49 PM	#4
Mart Senior Member Join Date: May 2010 Location: Solihull, England. Posts: 9,088	Re: Offenhauser heads with Auto Lite 216 plugs I run 216 plugs in my 8BA style Offenhauser heads. I used a countersink to take the last couple of threads out from the combustion chamber side of the head. I never thought of trying to lower the spotface, I wouldn't have had the tools to do it anyway. I was able to countersink them in a drill press using the stop to make sure they all went to the same depth. Mart.

11-26-2018, 05:13 PM	#5
qmdv Senior Member Join Date: Dec 2012 Location: Payette, ID Posts: 946	Re: Offenhauser heads with Auto Lite 216 plugs So has anybody used a longer plug

11-26-2018, 05:15 PM	#6
tubman Senior Member Join Date: Dec 2013 Location: Minnesota, Florida Keys Posts: 11,639	Re: Offenhauser heads with Auto Lite 216 plugs Sponsored Links (Register now to hide all advertisements) Stock Fords used 3/8" reach plugs. A lot of aftermarket aluminum heads seem to be designed to use 7/16" reach or even 1/2" reach plugs. This has always made sense to me, as aluminum is not quite as strong as cast iron, and the extra threads would add more holding power. Why anyone would want to go against this always amazes me. There are many spark plugs that will fit these heads perfectly. I first found this out in the early '60's when I had a "D-altered" coupe powered by a flathead. It had a set of Offenhauser heads on a '42 Merc engine. I screwed a set of stock plugs into the heads (when the were off the engine,) and saw that they were about 1/8" short. A friend of mine's father was a rep for Champion spark plugs and had all of the books and specifications for the entire line of plugs. We found that Champion specified "L" series plugs for Allards (which came with Ford flathead engines and Offenhauser heads at that time). I got a set and they fit perfectly. I think the engineers that designed the aftermarket heads knew what they were doing (if not, why buy their heads?), so we would be better off making the plugs fit the heads, not vice-versa. It's easy enough to screw a plug into an uninstalled head and see if it sits flush or not. Modifying a set of heads so as to be able to use the same spark plugs as a stocker seems like a real "rookie" move to me.

11-26-2018, 05:38 PM	#7
qmdv Senior Member Join Date: Dec 2012 Location: Payette, ID Posts: 946	Re: Offenhauser heads with Auto Lite 216 plugs The Autolite 216 has a 7/16 reach. The Autolite 4634 has a 1/2 reach

11-26-2018, 08:14 PM	#8
flatjack9 Senior Member Join Date: May 2010 Location: Oshkosh, Wi Posts: 4,600	Re: Offenhauser heads with Auto Lite 216 plugs Get a spark plug catalog. Pick the one that fits best. Why modify the heads?

11-26-2018, 09:58 PM	#9
4dFord/SC Senior Member Join Date: May 2010 Location: Columbia, SC Posts: 1,579	Re: Offenhauser heads with Auto Lite 216 plugs I use Autolite 437 plugs in my Offenhauser heads.

11-26-2018, 10:27 PM	#11
quickchange34 Senior Member Join Date: May 2010 Location: charlottesville, Va. Posts: 589	Re: Offenhauser heads with Auto Lite 216 plugs If using those heads try NKG B5ES They have a 3/4 reach .

11-27-2018, 10:59 AM	#13
tubman Senior Member Join Date: Dec 2013 Location: Minnesota, Florida Keys Posts: 11,639	Re: Offenhauser heads with Auto Lite 216 plugs "GOSFAST' - Very interesting. I did not know this as I have no experience with later Offenhauser heads. All I do know is that the vast majority of used heads I have gone through over the last 65 years either had carboned-up threads caused by running stock plugs or were crudely modified to allow the spark plug to be unshrouded. The former can be corrected, the latter usually not.