extended tip sparkplugs in our flatheads

[martybose]

So far, after talking to both Autolite and Champion engineers, I have been unable to find a 1/2" reach or a 3/4" reach standard tip plug that is designed for a .060" plug gap for an HEI ignition. I did find a couple of different 3/4" plugs designed for large gaps, but both were extended tips. The 3/4" reach is not a problem; I just bought 0.250" sparkplug spacers, which would allow me to use a 3/4" reach plug in a 1/2" reach head. My mechanic thought the extended tip might work.

So last night I was putting the top end of my motor back together, and decided to try these plugs. I installed two of the Autolites, one in #1 and the other in #6, and spun the motor over with the starter (no other plugs were in #2-5). When I pulled out #1, it looked fine, but the gap on #6 was hammered closed. I then compared the Autolites with the Champions, but the Champions were even taller than the Autolites. It appears that with a lot of effort you MIGHT be able to clock the electrodes so they missed the exhaust valves. Too much work for me, so I'm going back to my 1/2" reach AP425's, and malforming them enough to open the gap to 0.060". Looks a little funny, but it works, and the valves don't hit them.

Marty

[Suddensix]

Marty, what cylinder head are you using? I recently upgraded the plugs in my Edgy head and upon measuring the thread length discovered it was 7/16" and as I wanted a slightly hotter plug than the 306 Autolites I had been using ended up with #854 Champions. The Autolite # is 216. I'm using Pertronics ignition so set the gap at .040 which is .005 larger than suggested. So far so good.

[Don Coatney]

Marty;

The guy I bought my engine from (Bob Criswell) had a plug/valve clearance issue. He doubled up on plug gaskets and it worked for him. I am no sure exactly what his issues were.

[martybose]

Marty, what cylinder head are you using? I recently upgraded the plugs in my Edgy head and upon measuring the thread length discovered it was 7/16" and as I wanted a slightly hotter plug than the 306 Autolites I had been using ended up with #854 Champions. The Autolite # is 216. I'm using Pertronics ignition so set the gap at .040 which is .005 larger than suggested. So far so good.

I'm using an original Edmunds aluminum head. After finding a couple of damaged threads, I just had all of the cylinders upgraded to Timecerts.

I would suspect that your Edgy is nominally a 1/2" reach head, as I've never heard of a 7/16" reach plug. I hope that Champion is a 1/2" reach plug, because I guarantee you that the Autolite 306 is a 3/8" reach for cast iron heads.

Marty

[Suddensix]

I'm using an original Edmunds aluminum head. After finding a couple of damaged threads, I just had all of the cylinders upgraded to Timecerts.

I would suspect that your Edgy is nominally a 1/2" reach head, as I've never heard of a 7/16" reach plug. I hope that Champion is a 1/2" reach plug, because I guarantee you that the Autolite 306 is a 3/8" reach for cast iron heads.

Marty

There definately are 7/16" reach plugs as I did quite a bit of research on them. I agree tha Auto Lite 306's are 3/8." The plugs I'm using, Champ 854, were H10 in the old numbering system which were for flathead Fords.

[martybose]

There definately are 7/16" reach plugs as I did quite a bit of research on them. I agree tha Auto Lite 306's are 3/8." The plugs I'm using, Champ 854, were H10 in the old numbering system which were for flathead Fords.

I stand corrected; thanks for the info!

Marty

[Olddaddy]

I would contact Tom Langdon since he sells the HEI kits. He probably has a solution for the plugs as well.

[Plymouthy Adams]

Hi-jacking this thread..by seeing your new post...I take you have faired well through the tropical storm? Bezel arrived today..nice and thanks ever so much for bailing me out.

[Don Coatney]

I would contact Tom Langdon since he sells the HEI kits. He probably has a solution for the plugs as well.

Good luck. He will tell you he is an engineer but also that nobody on the internet knows what they are talking about. Having met him I was not impressed.

[1937 Dodge]

I am running a NOS Edmunds head with a Langdon HEI. Tom suggested that to take full advantage of the HEI, I should try to use a 0.060" gap. You could use smaller gaps and the car would still run OK.

I knew that my head had not been milled but that my block had a little taken off some years ago. In my case, I can run AC 45FFS plugs or AC 46FFS plugs. I could also run 44SX plugs.

If you are running an Edgy Head, I am sure that Earl would be the best person to talk to as he knows the design of his head you'd still have to check on how much was milled off of the block.

Problem with flatheads is we don't always know how much previous owners have shaved off of the block and head. Each person's engine clearance may be slightly different. I put a little putty at the tip of the plug that was gapped to 0.060 and turned the engine to see how much clearance I had. That in turn allowed me to select the best plug for my engine and still get the gap I wanted.