Piston Hitting Spark Plug on 88' 110 Johnson

[seapro42]

I just rebuilt both carberators on my 110 johnson. Tried to adjust linkage to get the best idle but it still coughed a little at low idle. Ran pretty well at high RPMs. Ran about 5 gallons of gas through it and all of a sudden it was only running off 3 out of 4 cylinders. Took it in and pulled the plugs. Realized the gap on my ql77jc4 champion plug in cylinder #1 was closed. The surface on the spark plug was rough indicating the piston had hit it several times. What caused this? Do I need to pull the head and check the piston for damage. Whats my next step, put a new plug in and see if it runs normal? Thanks for any feedback

 

[rodbolt]

Re: Piston Hitting Spark Plug on 88' 110 Johnson

pull the head. if the piston is marked up pull the rest of the motor down and find out what went through it. I would not bother with a compression test on that cyl as any trash may clog your gauge.

 

[seapro42]

Re: Piston Hitting Spark Plug on 88' 110 Johnson

rodbolt thanks for the reply. Pulled the head, piston looks good, no chips or any kind of damage visible. I'll put that back on with a new head gasket tomorrow. Before I pulled the head I bent the electrode on the sp 90 degrees from where its suppose to be set and put it back in, manually turned the flywheel and the piston never touched the sp. Can I put a new plug in and run it or is it likely the same thing will happen over time. I read somewhere to decarb the engine and then run. Is that some spray stuff like mercury Powertune that is just sprayed into the air intake while the engine is running.

 

[Dhadley]

Re: Piston Hitting Spark Plug on 88' 110 Johnson

Before you put the head back on check the piston for play. If a rod or wrist pin bearing is bad it will allow the piston to hit the plug once it gets bad enough.<br /><br />Also make sure thats the plugs your using and not the QL78YC. <br /><br />And the heads have not been surfaced, right?

 

[seapro42]

Re: Piston Hitting Spark Plug on 88' 110 Johnson

The spark plugs are not ql78yc.<br />I have never had the heads surfaced, but i've only had the motor for the past 2 years. Tomorrow I'll turn the flywheel so that the piston is in the out position and see if I can sense any play. Thanks for everyone's time.

 

[seapro42]

Re: Piston Hitting Spark Plug on 88' 110 Johnson

The piston does have some slop side to side but does not have any in the in and out direction of the cylinder. The piston right below it has the same degree of play. I guess my next step is to put the head on and see if it does the same thing with a new plug in. Thanks again

 

[Silvertip]

Re: Piston Hitting Spark Plug on 88' 110 Johnson

Check the plug that was damaged to see if the gasket was still there. It may have inadvertently been installed without it.