'98 Johnson with piston/plug contact!!

[ccarlson2004]

Hey all, I have a problem I'm hoping you guys can help me fix. My #1 piston has made contact with my spark plug the last 2 out of three fishing outings. It doesn't happen right away after firing, it will just happen out of no where, I'm not even sure if it happens at full throttle or less. I checked the other 3 plugs and they are fine. Plugs are less than a year old, and are all identical. I've also noticed that the piston has a small check mark from hitting the plug. Any suggestions?

 

[hidef]

Re: '98 Johnson with piston/plug contact!!

Need more info please. What model are we talking about here? Is it a Ficht or carbed?

 

[Cofe]

Re: '98 Johnson with piston/plug contact!!

Are you using Champion plugs? People have had problems with NKG plugs.

 

[Daviet]

Re: '98 Johnson with piston/plug contact!!

There is a gasket on the spark plug isn't there?

 

[ccarlson2004]

Re: '98 Johnson with piston/plug contact!!

thanks for replying. Model is 90hp SPL not carbed.

 

[ccarlson2004]

Re: '98 Johnson with piston/plug contact!!

Yes they are champion plugs and yes there is still a gasket.

 

[Daviet]

Re: '98 Johnson with piston/plug contact!!

I would check the piston/rod to see if there is any play in it.
Remove all the plugs, insert a slinder screw driver into the cylinder and hand rotate the flywheel until the piston comes up to TDC, rotate the piston on the down stroke and then push on the screw driver. Do you feel any slack in the piston?

 

[Cofe]

Re: '98 Johnson with piston/plug contact!!

Yep like Daviet said.......I agree.....

 

[ccarlson2004]

Re: '98 Johnson with piston/plug contact!!

okay i did that process three times. the first time i felt just a little bit of movement, but the following 2 times there was no movement.

 

[Daviet]

Re: '98 Johnson with piston/plug contact!!

Little bit = how much, 1/16" 1/8". You can repaet the test while moving the piston from the top all the way to the bottom of the cylinder.

 

[ccarlson2004]

Re: '98 Johnson with piston/plug contact!!

little bit as in i couldn't see movement, i thought i maybe felt something. i just tried again and i wasn't able to make it move at all, i suppose it could have been my imagination...hopefully.

 

[Daviet]

Re: '98 Johnson with piston/plug contact!!

Usually if they are loose you will feel and maybe hear a slap.
Any carbon buildup on the top of the pistons?

 

[ccarlson2004]

Re: '98 Johnson with piston/plug contact!!

no buildup is present

 

[Daviet]

Re: '98 Johnson with piston/plug contact!!

Well , the only way a piston is going to hit the plug is to have slack in the rod/wrist pin bearing or carbon build up on the piston.
I guess there could be a head gasket, head problem but I would think it would happen all the time if that was it.
I once worked on an engine that had 2 washers on a plug, I asked the owner if he knew anything about it. He said if he only put 1 gasket on it would close the gap on the plug. I did some checks and couldn't find any problems, so I installed 2 gaskets on the plug, that was probably 4-5 years ago and the engine is still running strong. Still don't know why it would close the gap up.

 

[ccarlson2004]

Re: '98 Johnson with piston/plug contact!!

yea it's def interesting. i may try that if i can't come up with anything else. Thank you for all your help Daviet!

 

[Daviet]

Re: '98 Johnson with piston/plug contact!!

Not sure I was much help, but you're welcome.

 

[guy74]

Re: '98 Johnson with piston/plug contact!!

What is your history with this engine? If it is relitively new to you, is it possible it has had that head surfaced? If it was mine, and I couldn't feel any slack in the rod, I would put an extra gasket under the plug and run it. just keep an eye on it.

 

[ccarlson2004]

Re: '98 Johnson with piston/plug contact!!

the boat/motor has been my dads until 2 years ago, but this problem has only started this year. Hopefully an extra gasket will solve my problem.

 

[Daviet]

Re: '98 Johnson with piston/plug contact!!

Keep us informed, inquiring minds want to know.

 

[boobie]

Re: '98 Johnson with piston/plug contact!!

If you could post the exact model # of the mtr and what champion plugs you're using that would help.