AutoLite 216's in Offy heads

[qmdv]

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.

[19Fordy]

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.

[tubman]

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.

[tubman]

Originally Posted by 19Fordy

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.

[russcc]

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.

[drolston]

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Originally Posted by russcc

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.

[qmdv]

Originally Posted by drolston

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

[Tim Ayers]

Originally Posted by qmdv

Will check valve clearance and if OK I will either go with Champ L78C or maybe NGK BR7ES

NGK over Champions.

[tubman]

"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.

[qmdv]

Originally Posted by tubman

"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

[tubman]

Originally Posted by qmdv

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.

[jimvette59]

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.

[tubman]

Originally Posted by jimvette59

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.

[flatford8]

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

[GOSFAST]

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

[19Fordy]

Got to admire the tech skills of GOSFAST.

[GOSFAST]

Originally Posted by 19Fordy

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.

[qmdv]

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

[estout81]

My fix. Simple and runs very well. I use Autolite 4092 or 4093 plugs.

[qmdv]

Originally Posted by estout81

My fix. Simple and runs very well. I use Autolite 4092 or 4093 plugs.

Not seeing the fix.

[estout81]

Chamfer the plug hole.

[tubman]

Originally Posted by estout81

Chamfer the plug hole.

Are you kidding? Gary "GOSFAST" who is a professional engine builder has already given you the answer. Hell, I'm just an amatuer, and even I knew better. Autolite 216's (7/16" reach) in a a spark plug hole almost 3/4" deep? "Chamfering" the spark plug hole? These are aluminum heads; The manufacturers designed them with a longer reach because aluminum is not as strong as cast iron. What are you guys thinking?

[qmdv]

I will be putting in a set of AutoLite 425's this afternoon. 1/2 inch reach. What do you think the minimum clearance should be between the exhaust valve and the spark plug grounding lug.

[estout81]

Tubman,
Have you notified Briggs & Stratton of their design error?

[Tim Ayers]

Am I missing something here? Why not get the proper reach plugs instead using what's on hand?

Rock Auto sells most of their plugs for under $2 a piece (NGK, Bosch, Autolite, etc.).

[qmdv]

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Originally Posted by Tim Ayers

Am I missing something here? Why not get the proper reach plugs instead using what's on hand?

Rock Auto sells most of their plugs for under $2 a piece (NGK, Bosch, Autolite, etc.).

That is what I am trying to figure out. I think the 375 Offy heads have less clearance than the 400's and 425's

[Bored&Stroked]

There are many ways to skin this cat - heck, I'd just pick one. You can run longer plugs with 'shims' (I'd prefer them to be made of copper), you can chamfer/change the bottom portion of the head chamber-side (chamfer/blend), you can machine steel or aluminum inserts and machine the original threaded holes to insert them - these can do TWO things:

1) Gives you a specific length and quality of thread as far as wearing out over time. Many of us have experienced that sickening feeling when you tighten a plug and the old aluminum threads give way . . . boy does that suck.

It usually happens when you are in a hurry to get someplace, are far away from home and your tools and/or have no time to now pull the heads and "fix" them . . . . that 'Murphy' is a rotten Devil!

2) You can make the threaded inserts to support 3/4" reach plugs - which are by far the most common and give you a ton of different heat ranges, suppliers, etc..

Keep in mind that folks like Edelbrock retooled most of their patterns (if not all) and machining operations to produce heads that take 3/4" reach plugs . . . a very smart thing to do! This is one reason I use Edelbrock heads on many modern builds.

[drewbaby]

I had the same problem with a slight miss with the same bore/stroke engine. I found the low speed jet to be a little lean. Standard size I believe was .029ths. I drilled it out to .031ths. Runs Fine. Hope this helps, wasn't spark plug related.

[estout81]

Autolite 216 plugs have a 7/16 in. reach, A8 heat range and non res. 425's have a 1/2 in. reach, B9 heat range and are resistor. 4092's are 1/2 in. reach, A9 heat range and non res.
My Offy 400 heads had about 5/8 in. of threads. I used the Autolite 4092 plugs and chamfered the combustion side to remove the excess head threads. For clearance of plug to valve, anything over 1/16 in. should be plenty. I did this several years ago and many miles and the engine runs fine.

[35fordtn]

For those curious about the shins McMaster Carr has the 14mm copper shins .052” thick relatively cheap.

[tubman]

Originally Posted by estout81

Tubman,
Have you notified Briggs & Stratton of their design error?

Since we are talking high performance heads here, I think you just made my point.

[qmdv]

Originally Posted by estout81

Autolite 216 plugs have a 7/16 in. reach, A8 heat range and non res. 425's have a 1/2 in. reach, B9 heat range and are resistor. 4092's are 1/2 in. reach, A9 heat range and non res.
My Offy 400 heads had about 5/8 in. of threads. I used the Autolite 4092 plugs and chamfered the combustion side to remove the excess head threads. For clearance of plug to valve, anything over 1/16 in. should be plenty. I did this several years ago and many miles and the engine runs fine.

Did a search on auto lite sited and could find nothing that tells me what A9 and B9 are

[Tim Ayers]

Originally Posted by tubman

Since we are talking high performance heads here, I think you just made my point.

Wait, now I'm even more confused. Tubman, are you saying chaffering the head decreases performance?

[tubman]

I'm saying that the heads were designed specifically to have a longer reach because aluminum is not as strong as cast iron and requires more thread length to provide the proper amount of support for the spark plug threads. Chamfering the plug holes reduces the designed thread length and weakens the holding power of the threads in the head. I also believe that thoughtlessly modifying well-engineered designs is not a good idea. I am also saying that anyone that looks to Briggs and Stratton for tips and tricks to upgrade the Ricardo combustion chamber design to improve performance is barking up the wrong tree.

Just about every set of used heads I have ever seen had at least one stripped spark plug hole if not several. Those threads are there for a reason, and I don't think eliminating any is a good idea. Even if enough threads are removed to be visually pleasing , the plug is still shrouded to some degree.

Bottom line is that I don't think it is a good idea, especially when people with the experience and knowledge required to build performance engines have already provided a better alternative.

[Tim Ayers]

OK, got it. Thank you for clarifying. Not sure why I'm having such a hard time following the progression of this thread.

I am pulling out something you said though. the Ricardo combustion chamber

I thought only Harley and some very rare Model A heads were able to utilize Ricardo's chamber design. Something about head bolts being in the way with the a V8. I could be totally off base on this.

[tubman]

Here's what the internet said :

A "Ricardo" type cylinder head had the spark plug and the main combustion chamber placed over the valves of the ell type head engine. The volume of this chamber was considerably larger than the small clearance space provided above the piston and the transition throat that connected this space to the main combustion chamber. As the piston approached the top of its compression stroke, the fresh air/fuel charge was squeezed, or squished, through the ever narrowing transition throat. The rush of the increasingly dense air/fuel charge through this transition throat created considerable turbulence in the combustion chamber. When the spark plug ignited the turbulent mixture, the flame front spread fast resulting in quicker, smoother, more complete burn of the fuel, reducing spark plug fouling and lowering the exhaust temperature. This resulted in more, smoother, power, better fuel economy and was less susceptible to detonation than the slower burn of a relatively stagnant mixture of a main combustion chamber above the piston in previous cylinder head designs.

This describes a flathead Ford combustion chamber to me, and explains why it is so important to have minimum clearance over the piston top and the head, which most of us try to achieve.

[Tim Ayers]

Thank you, Tubman.

What am I thinking of then? I know Harley used this specific chamber design in their racing flatheads. I thought it was designed by Sir Richard Ricardo. I think Frank Otto's book has a chapter on it. Let me look it up.

[tubman]

It was Sir Harry Ricardo. I believe the Harley racing flathead was the final and best application of his theory and worth emulating. The same can't be said for Briggs and Stratton.

[Tim Ayers]

Originally Posted by tubman

It was Sir Harry Ricardo. I believe the Harley racing flathead was the final and best application of his theory and worth emulating. The same can't be said for Briggs and Stratton.

Haha. Sounds good!

[qmdv]

Originally Posted by tubman

It was Sir Harry Ricardo. I believe the Harley racing flathead was the final and best application of his theory and worth emulating. The same can't be said for Briggs and Stratton.

I gave my book "The High-speed Internal-combustion Engine" by Sir Harry R. Ricardo to a grandson. He loves it

[qmdv]

Originally Posted by GOSFAST

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!

If I did this the exhaust valve would hit the plug.

Where I grew up there was a speed shop in Glendale, CA on Victory Boulevard. When they handed over a new set of 375 Offy heads I wonder what plugs they offered the customer.

[JSeery]

Originally Posted by qmdv

If I did this the exhaust valve would hit the plug.

Where I grew up there was a speed shop in Glendale, CA on Victory Boulevard. When they handed over a new set of 375 Offy heads I wonder what plugs they offered the customer.

So your saying a .625 inch reach plug would hit the exhaust valve?? Then why wouldn't a .125 shorter plug at .500 work?

[estout81]

I don't think a flathead will ever see 1500 PSI cylinder pressure. A 14mm plug has about a 1/4 sq. in. surface so, .25 x 1500 = 375. Don't think that will blow out a spark plug.

[qmdv]

Originally Posted by JSeery

So your saying a .625 inch reach plug would hit the exhaust valve?? Then why wouldn't a .125 shorter plug at .500 work?

Will be looking for Autolite 4092's tomorrow. That will give right close to .050 clearance.

[estout81]

JSeery,
See post 19. The picture shows Autolite 4092 plugs [ 1/2 in. reach]. The chamfer takes out a little less than a 1/8 in.

[JSeery]

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Originally Posted by estout81

JSeery,
See post 19. The picture shows Autolite 4092 plugs [ 1/2 in. reach]. The chamfer takes out a little less than a 1/8 in.

That's where I'm getting lost I guess. 1/8 in = .125 So if you add the .125 to the plug reach you get .500 + .125 = .625 which is what the long reach plugs with the spacers are and no chamfer is required. What am I missing here and how would this cause the plug to hit the exhaust valve? Is the valve at maximum lift that close to the roof of the cylinder? If it is, then the plug is going to have to be shrouded up in the threads or the plug is not going to be able to have an extend electrode below the thread surface of the plug.

[qmdv]

Originally Posted by JSeery

That's where I'm getting lost I guess. 1/8 in = .125 So if you add the .125 to the plug reach you get .500 + .125 = .625 which is what the long reach plugs with the spacers are and no chamfer is required. What am I missing here and how would this cause the plug to hit the exhaust valve? Is the valve at maximum lift that close to the roof of the cylinder? If it is, then the plug is going to have to be shrouded up in the threads or the plug is not going to be able to have an extend electrode below the thread surface of the plug.

How is chamfering out 1/8 in the chamber adding to the reach. Since the heads are installed and am not inclined to pull them I will just put in the 4092's and see how it runs.

[JSeery]

Originally Posted by qmdv

How is chamfering out 1/8 in the chamber adding to the reach. Since the heads are installed and am not inclined to pull them I will just put in the 4092's and see how it runs.

Who said anything about the chamfer increasing the reach?? I was attempting to understand how adding a spacer ring would increase the reach, as in cause interference between the plug electrode and the exhaust valve.

I normally like these type of discussions, but I have to admit I can't understand this one at all. Guess I just need to accept defeat (in my ability to follow the discussion) and move on.

[Tim Ayers]

Originally Posted by JSeery

Who said anything about the chamfer increasing the reach?? I was attempting to understand how adding a spacer ring would increase the reach, as in cause interference between the plug electrode and the exhaust valve.

I normally like these type of discussions, but I have to admit I can't understand this one at all. Guess I just need to accept defeat (in my ability to follow the discussion) and move on.

I'm with you. I gave up a few days ago. I'm not placing blaming on anyone, I am just having a terrible time following the progression.

This is something I'd need to see in front of me in order to make heads or tails of it.

[Bored&Stroked]

Too many cats . . . and too many cat skinners it seems . . .

[GOSFAST]

We've been using the .125" spacer for over 35 years now, never a single issue??

I've personally had numerous discussions with both Tay (Offenhauser) and Vince (his "main" man), that have gone nowhere, like beating a dead horse. What we've learned over here is stay with the Edelbrock's, they got their act together. Always have for the most part! My only issue with them really was over the "enlarging" of the head bolt holes back when. This is non-issue here, as we "pin" all heads and blocks together anyway!

Thanks, Gary in N.Y.

P.S. "JSeery", I'm also sort of confused myself here, but I do know your thinking is OK!

[qmdv]

Then let me try again. I have offy 375 heads. With exhaust valve fully open there is .615 between the top of the exhaust valve and the spark plug mating face on top of the heads. If I used 3/4 reach plugs with a .125 spacer, the plug would interfere with the valve and that would be bad news. I was hoping that somebody had some help they good give. This task would be a lot easier if I had heads with deeper combustion chambers.

[tubman]

Just one question. Are these new or used heads?

[qmdv]

Originally Posted by tubman

Just one question. Are these new or used heads?

Probably at least 60 years old. Very good condition. I do believe that Offy only makes 400's and 425's today

[Bored&Stroked]

Given that the valves are angled and the actual location of the spark plug hole and that a standard head gasket is about .052 thick, are you measuring the clearance at the location where the spark plug is oriented to the valve (with a head gasket in place) - or the top side of the valve (toward the intake) - which has a different height?

Consider that your particular block, cam, head, valve seat depth, valve type combination is specific to your particular motor - nobody can tell you exactly what to do. The answer is "it depends" . . . on a lot of different factors. In the end, the dimensions are what drives your options - plain and simple.

All you need to do is clay the top of the valve at full lift - with a head gasket in place and a couple studs/bolts and see what the exact amount of clearance you have above the valve in the exact location. Then, you know what you have to work with - and can determine how deep the plug can go.

Once you know that, then you can determine which plugs you can use (given the length, heat range and electrode type) and how many potential spacers (or not) you need to utilize. You'll have options as to how you want to address your specific dimensions. If you need a shorter reach plug (and then have threads showing in the chamber side), you can chamfer and also maybe add a power-slot in the head as Gary has shown.

There are lots of ways to address any potential issue - just decide which plugs you want to run and therefore what you need to do.

Good luck!
B&S

[qmdv]

The heads are installed with the gasket in place. I am measuring through the spark plug hole from where the spark plug mates to the head to the valve face when it is fully open.

[GOSFAST]

Originally Posted by qmdv

Then let me try again. I have offy 375 heads. With exhaust valve fully open there is .615 between the top of the exhaust valve and the spark plug mating face on top of the heads. If I used 3/4 reach plugs with a .125 spacer, the plug would interfere with the valve and that would be bad news. I was hoping that somebody had some help they good give. This task would be a lot easier if I had heads with deeper combustion chambers.

Just to keep things clear here, you don't necessarily need the .125" spacers, you can make them any length to get the job done!

The .125" spacers happen to fit the Offy heads we generally work on here!

Thanks, Gary in N.Y.

P.S. Here's an example, if you start with the .750" plug and make the spacers .250" you now have a .500" reach plug. You also need to consider the plug washer thickness, .025" (nominally).

[qmdv]

Originally Posted by GOSFAST

P.S. Here's an example, if you start with the .750" plug and make the spacers .250" you now have a .500" reach plug. You also need to consider the plug washer thickness, .025" (nominally).

So what is the advantage of a 3/4 reach with a .250 spacer over a 1/2 reach plug.
Oh these are very old heads. probably older than the average age on this forum. Who knows what has been done to them as they are not talking to me. Wishing now that I had bought new Edlebrocks

[Bored&Stroked]

The advantage of 3/4" reach plugs is that you have the widest selection of brands, insulator types, heat ranges, plug application types, etc.. If you've found a 1/2" reach plug that you like, no real reason to go to all the effort to worry about 3/4" reach plugs - but you asked the question.

[Mart]

I have offenhauser heads on the French motor in my roadster. I run 216s. A few years ago I did what I thought at the time was the clever thing to do and chamfered the holes from the underside. It runs great and never caused me concern. If I were doing it today I might reconsider and try and use a longer plug.
Fingers crossed I'll get away with it.
Mart.

[qmdv]

Originally Posted by Bored&Stroked

The advantage of 3/4" reach plugs is that you have the widest selection of brands, insulator types, heat ranges, plug application types, etc.. If you've found a 1/2" reach plug that you like, no real reason to go to all the effort to worry about 3/4" reach plugs - but you asked the question.

Great points. I have learned a bunch and have had a few calls from some folks. Thanks to all

[Phil Gillespie]

It shows the reason to fit a couple of plugs into head proir to fitting.
Easy to measure and set up with heads off. Which I hope to be doing in near future.
Phil NZ

[mfirth]

I ran 216s in mine for 3 years with no mods and no problems.

[tubman]

Originally Posted by Phil Gillespie

It shows the reason to fit a couple of plugs into head prior to fitting.
Easy to measure and set up with heads off. Which I hope to be doing in near future.
Phil NZ

Unfortunately, this is probably mandatory with Offenhauser heads, both new and used.