cylinder hitting my spark plug?

[joho5]

1971 Johnson 9.5

Ok, I recently put on a new cylinder head (brand new out of the box) and a head gasket. I also replaced the spark plug wires, ignition, etc...

anyways, I got it all put back together after testing and seeing a good spark on each plug. It wouldnt start for nothing. I pulled my plugs back out to check them to see for fouling or wet and come to find out that they are now being contacted by the piston. The piston is knocking them flat. Its not hitting them too hard because its just causing a slight scratch on the top of the piston. They are new spark plugs...the NGK conversion of the ones my motor calls for.

Could it just be the plug? Surely the cylinder head is fine right?

I was just wondering if this might be a common problem, or what I should do.

thanks

 

[lbentz]

Re: cylinder hitting my spark plug?

yes, I had this issue before. Unfortunately. eventhough NGK makes a great plug, their shanks are too long for outboard applications and the pistons will hit them. I guess the engineers at NGK must have went out for a 5 Martini lunch, before they decided to do this. the problem is not with the work you did on your motor, so you're good. Go get a pair of J6C's in put them in, and you'll be fine.

Good luck.

 

[joho5]

Re: cylinder hitting my spark plug?

ok i will do that...actually the top one is the one that is hitting. the bottom cylinder might be too, but it doesnt bend it all the way back.

I will try the J6C's and see what happens. I was wondering because head that I replaced didnt have this problem and I was like all I did was put a new one on.

thanks man

 

[joho5]

Re: cylinder hitting my spark plug?

I had my old J6C's and they are fine. The NGK's looke actually like the whole wrong spark plug. They are longer. I just trusted the guy at the part store to do the correct conversion of plugs.

 

[lbentz]

Re: cylinder hitting my spark plug?

Yea, unfortunately the parts guys just go by the book. Some outboards have the plugs mounted in at an angle and you could possibly get away with running the NGK's, but most straight in spark plug holes won't allow them. It seems that they are about 1/16 - 1/8 inch longer than the champions on the threaded shank.