I may have shot myself in the foot!!

[bosworth]

Recently I had my 218 engine rebuilt and last week in installed a  "mini" HEI distributor, wires and plugs from Langdons.  The plugs provided were RJ18YC6 with  a .060 gap.  I haven't been all that impressed with the sound or the performance of the engine so today I pulled the plugs and did a compression test,  two at 135 psi four at 140,  so that seemed OK,  I examined the plugs and noticed that each had been hitting a valve,  one was no longer .060 but down to .020  I am concerned about how much damage I might have done to the valves in my new engine.  I replaced the plugs with a set of Autolite 85's that I had. I gapped them to .055. It runs better but not as smooth and quiet as I had hoped at 55 to 60 mph. I am not at all anxious to pull the head,  I wonder if I should just run it and be happy or if I should be digging deeper. I will send Tom Langdon a note about the problem with the plugs.  It might not be a common problem but  the block was decked and the head was surfaced so things might be a little closer than normal.  I think I'd better get some bandages on my damn foot!

Bill

[Plymouthy Adams]

if you just hit the tip and closed the gap......you have done nothing internally except mess up your tune......I think I would look to an added gasket to the base of the spark plug....

[bosworth]

I wondered about adding a gasket or shim, didn't know if that was kosher.  

[Plymouthy Adams]

this is on the same line as indexing plugs for performance tuning....

[kencombs]

I'd try an extra gasket.  But, the best solution would be to find a plug with similar heat range, but not off the projected tip design.  Those are much longer than the stock recommended plug.

[Veemoney]

I agree with what has already been said. I will just add that you can measure the RJ18yc6 plugs as bent to give you the max depth of protrusion for plugs as you look for a new plug or shim combo. Just make sure to add some buffer margin. 

[bosworth]

Thanks all;

I spoke with Tom Langdon,  he said that from the hundreds of sets of plugs that he has sold,  this problem only happened one before, I guess my block and head have been milled enough to cause the problem,  tom said that I could use the RJ18C6 (without the y) as it doesn't project as far into the cylinder.  I have Autolite 306's in there for now, seems to be running ok.

thanks again;

Bill

[Mike36]

Do yourself a favor, leave the Autolites in it. I would NOT use Champion plugs if they were free.

[Plymouthy Adams]

I feel the same....I often wonder why the cars off the dealer lot runs so good and like forever without fail with champions and yet you put in a replacement set and whamo at least 40% failure rate it seems.  Makes  you wonder if they test and sell these OTC units as seconds.