Spark Plugs gap bent back after test run 1957 35hp

[Squirrel42]

Boat died out in the middle of the lake on my test run, I removed the spark plugs to find them bent back to the electrode.

Come to find out I had the wrong spark plugs in, and I'm wondering if they are threading in to far and the piston is slapping them.

I had L77jc4 plugs in and the recommended plugs are J64 with a much shorter thread base.

I was able to replace the top with a spar J64 plug from my tool box but the bottom was cross threaded and would not except the smaller thread.
So I re-gaped and put the L77jc4 back in so I could limp back to the dock. When I got back home i checked the top plug and it was fine but the bottom
L77jc4 plug was bent back again.

Any suggestions on where i should go from here? I want to buy a new cylinder head but was waiting to hear from someone about this issue.

 

[jimmbo]

Why do you want a new cylinder head?

I recall the 57 35hp was speced with J6J, champion doesn't show a 35hp in its charts anymore. J6C or 841 cross reference to it

If the L77jc4 is too long you're lucky if you haven't damaged the piston

 

[Squirrel42]

Yeah.. I'm afraid I did damage the Pistons. The bottom plug thread is stripped but I might tap it and repair it.

I guess that's why the previous owner had these plugs installed because the short one won't thread in.

I just wanted to know if it was in fact too long. Learned the hard way, lucky I got back to the dock.

 

[jimmbo]

If the piston hit it, it is too long. How bad is the damage to the piston? Pic please

 

[F_R]

Those pistons are pretty darn thick at the top. I doubt you hurt it any. Put the right plugs in and go with it. Yeah, the hole can be repaired.

 

[Squirrel42]

Definitely some notches ware the pistons met the spark plugs. I gotta repair the cylinder spark plug hole, so I'll take a look at the walls while I'm in there.

 

[thumbnut]

Not to add worry....but I had bought 2 pistons with rods from ebay for my '76 omc15. One had what looked like a half moon indent on the piston top from a 3/4 inch reach plug. And that rod was kinked. Looks as if the piston only hit the ground electrode on yours..just sayin..