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Old 08-19-2020, 05:24 PM   #1
qmdv
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Default AutoLite 216's in Offy heads

Just got a recent rebuild running. 59 AB block 3 5/16 by 4" stroke. Offy 375 heads, mild cam of unknown origin. Using AutoLite 216's cus I had them. It misses now and then, pulled plugs to find a bit of carbon. Also I am thinking that a longer reach plug would be better. Not sure how smart it is to have spark plug hole threads exposed in the combustion chamber.
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Old 08-19-2020, 05:38 PM   #2
19Fordy
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Default Re: AutoLite 216's in Offy heads

I am no expert but, I think having plugs where the firing tip is inside the threaded recess results in fouling. Try a plug with a longer reach. Make sure plug doesn't hit the piston.
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Old 08-19-2020, 05:52 PM   #3
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Default Re: AutoLite 216's in Offy heads

There were a couple of discussions, both here and on the H.A.M.B. about he proper length plugs for Offenhauser heads. The general conclusion was that they don't seem to be designed for any particular length plug, and that for optimum use, spacers need to be used. Here's a link to one thread on the H.A.M.B. : https://www.jalopyjournal.com/forum/...#post-13317505. (It's interesting that the H.A.M.B. thread ends up pointing back here to "The Barn".)

Note that it ends with "flatjack" (who really knows his stuff) saying that the equivalent of a Champion "N" series needs to be used with a .21 spacer.

In any event, stock 7/16" reach plugs are not correct for use with Offenhauser (and most other aftermarket) heads.
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Old 08-19-2020, 05:53 PM   #4
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Default Re: AutoLite 216's in Offy heads

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Originally Posted by 19Fordy View Post
I am no expert but, I think having plugs where the firing tip is inside the threaded recess results in fouling. Try a plug with a longer reach. Make sure plug doesn't hit the piston.
The plugs won't hit the piston, but they will hit the exhaust valve with equally unfortunate results.
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Old 08-19-2020, 06:58 PM   #5
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Default Re: AutoLite 216's in Offy heads

What I used in the Navarro heads were Champ L78Cs with a 1/2"reach. It left about 1 & 1/2 threads exposed which I countersunk to eliminate them. They don't hit the exhaust valves with a 1007B cam, that has about a .350 lift on the exhaust & .365 on the intake.
I used old stock Autolite plugs washers as they were thinner than Champs to position the plug so less thread were exposed.
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Old 08-19-2020, 08:04 PM   #6
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Default Re: AutoLite 216's in Offy heads

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What I used in the Navarro heads were Champ L78Cs with a 1/2"reach. It left about 1 & 1/2 threads exposed which I countersunk to eliminate them. They don't hit the exhaust valves with a 1007B cam, that has about a .350 lift on the exhaust & .365 on the intake.
I used old stock Autolite plugs washers as they were thinner than Champs to position the plug so less thread were exposed.
Ditto on the Champ L78C plugs for my 59A/B with Offy .425 heads. I did not countersink. Running Schneider 248f cam with .350 lift.
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Old 08-19-2020, 09:02 PM   #7
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Default Re: AutoLite 216's in Offy heads

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Ditto on the Champ L78C plugs for my 59A/B with Offy .425 heads. I did not countersink. Running Schneider 248f cam with .350 lift.
Will check valve clearance and if OK I will either go with Champ L78C or maybe NGK BR7ES
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Old 08-19-2020, 09:30 PM   #8
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Default Re: AutoLite 216's in Offy heads

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Will check valve clearance and if OK I will either go with Champ L78C or maybe NGK BR7ES
NGK over Champions.
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Old 08-19-2020, 09:49 PM   #9
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Default Re: AutoLite 216's in Offy heads

"L" series Champions and equivalents are too short and "N" series are too long. That's the conclusion that was reached before. The "L" series will be shrouded, but not as bad as stock plugs. I believe the proper plug is an "N" series with an appropriate spacer.

Years ago I ran some marine surface gap plugs in a 276" Merc with Offy heads and an MSD ignition. The surface of the plugs were flush with the inside surface of the head, and they worked great. They were designed for an electronic ignition system that produced a very hot spark. The MSD was up to the task of producing a hot spark, but it would eat the coil wire tower in the distributor cap in about 6 months, requiring cap replacement.
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Old 08-19-2020, 09:59 PM   #10
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Default Re: AutoLite 216's in Offy heads

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Originally Posted by tubman View Post
"L" series Champions and equivalents are too short and "N" series are too long. That's the conclusion that was reached before. The "L" series will be shrouded, but not as bad as stock plugs. I believe the proper plug is an "N" series with an appropriate spacer.

.
Where to find the spacers
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Old 08-20-2020, 06:30 AM   #11
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Default Re: AutoLite 216's in Offy heads

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Originally Posted by qmdv View Post
Where to find the spacers
Perhaps here? https://www.speedwaymotors.com/Spark...ampaign=CSEGOO.

I have not yet had the need for tham, as I am partial to Edmunds heads because of the spark plug placement, but I am "keeping my hand in" since I have a new set of OFFY 8BA heads on the shelf.
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Old 08-20-2020, 06:57 AM   #12
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Default Re: AutoLite 216's in Offy heads

With the heads off the area where the spark plug lands can be lowered by using the tool from a spark plug thread repair kit.
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Old 08-20-2020, 07:24 AM   #13
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Default Re: AutoLite 216's in Offy heads

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Originally Posted by jimvette59 View Post
With the heads off the area where the spark plug lands can be lowered by using the tool from a spark plug thread repair kit.
I like this idea, although you will be reducing the amount of threads holding the steel plug into the aluminum. Edelbrock and the others seem to work fine with 1/2" reach ("L" series) plugs, though.

I wonder if maybe there once were "M" series plugs, half way between "L"'s and "N"'s.

BTW, not recommending Champion's here, just using their thread length nomenclature because it's easy to understand. I do use Champion extended tip plugs in the Edmunds heads.
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Old 08-20-2020, 08:17 AM   #14
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Default Re: AutoLite 216's in Offy heads

I’m not running aluminum heads right now, but I have given up on Autolite 216’s. I’ve had too many that the electrode pulled right out of the plug ..... Mark
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Old 08-20-2020, 08:41 AM   #15
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Default Re: AutoLite 216's in Offy heads

Offenhauser has always been a problem with getting the spark plugs where they should be sitting?

Over here we use the Autolite 3924, .750" reach, with a .125" spacer on the top side!

Occasionally we also "fire-slot" the spark plug holes on many builds!

Thanks, Gary in N.Y.

P.S. We make our own spacers as needed for each individual job in the door with Offy heads. See photos below here. The left photo has a .750" reach plug with a .125" spacer up top
Attached Images
File Type: jpg Flathead Offy Head - .750 Long Plug-.125 Spacer.jpg (72.1 KB, 91 views)
File Type: jpg Spark Plug Shims-Washers A.JPG (86.4 KB, 86 views)
File Type: jpg Flathead Offy Head-Modified.JPG (63.9 KB, 82 views)
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Old 08-20-2020, 11:18 AM   #16
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Default Re: AutoLite 216's in Offy heads

Got to admire the tech skills of GOSFAST.
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Old 08-20-2020, 11:47 AM   #17
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Default Re: AutoLite 216's in Offy heads

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Originally Posted by 19Fordy View Post
Got to admire the tech skills of GOSFAST.
Much appreciated, we are always trying to improve on things as we move along??

Thanks, Gary in N.Y.

P.S. Due to a couple issues on one of my more recent builds and more from what I read up here we are trying to "correct" two different items, the first one being any annoying oil pan leaks, and the second one being sealing up head studs WITHOUT any sealer in the program! This would be for head studs only, not head bolts. The latter we are working on now, the pan issue will come a bit later! I would definitely still use some sealer on the studs but we want any leaks stopped first without it's use! The sealer would be as a "backup" so to speak.

Last edited by GOSFAST; 08-22-2020 at 05:00 PM. Reason: C
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Old 08-22-2020, 04:38 PM   #18
qmdv
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Default Re: AutoLite 216's in Offy heads

Been out of town and just measured from the face of the head (where the plug washer sits) to the top[ of the exhaust valve in fully open position. Measures .615. so 3/4 reach is out of the question. Searching various plug specifications. The AutoLite 216 looks like a pretty cold plug. Maybe just get a hotter plug in that series
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Old 08-22-2020, 05:43 PM   #19
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Default Re: AutoLite 216's in Offy heads

My fix. Simple and runs very well. I use Autolite 4092 or 4093 plugs.
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Old 08-22-2020, 06:01 PM   #20
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Default Re: AutoLite 216's in Offy heads

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My fix. Simple and runs very well. I use Autolite 4092 or 4093 plugs.
Not seeing the fix.
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