Electrode on spark plug smashed closed while running

[Jonbmyers]

I have a 50 hp merc 3 cyl 2 stroke. On the lake last weekend while at full power all the sudden I could tell I lost a cylinder. I got home and removed the plugs (suspected a fouled plug) to my surprise cyl2 plug had the electrode touching the anode. From my experience with cars this only happens from contact with the piston. Parts man at Bass Pro confirms im using the correct plugs. My question is- How can I check the piston assembly for problems without taking the whole darn thing apart? Is there a cover i.e like a head on a car that can be removed for a quick inspection? If not is this likely a rebuild coming soon type thing? Thanks for the input.

 

[Maxz695]

Re: Electrode on spark plug smashed closed while running

take a pencil or the like and see if you can feel alot of play when the piston is turning either at TDC or at the lowest part of the stroke to give an indication of something worn out

 

[Jonbmyers]

Re: Electrode on spark plug smashed closed while running

Thanks Ill give it a try.

 

[Silvertip]

Re: Electrode on spark plug smashed closed while running

Use a small LED pen light and look into the spark plug hole with the piston at the top of the stroke. If you see a contact mark, there is very likely an internal problem. Did you hear any odd noise just before the cylinder went dead? Although it si possible a chunk of carbon came loose, I doubt that's the issue. Just for the record, what plug brand and number were you using and were they newly installed?

 

[Maxz695]

Re: Electrode on spark plug smashed closed while running

you can also mark the flywheel TDC on all three and mark it when you feel movement on the other two cylinders mark back and forth till moment then measure for inconsistancy

 

[Jonbmyers]

Re: Electrode on spark plug smashed closed while running

The spark plugs are NGK I couldnt tell you the number right now though, but I was told by the parts guy they were proper. Being the fact that I have only owned this boat for 2 months this is just my luck. Im just afraid I may have a broken rod or a messed up piston. Either way thanks for the advice and I will see what I can come up with. Im a rookie to marine engine so it will probably take me a while to figure it out. Good thing its coming inot winter I will have plenty of that.

 

[Capt Ken]

Re: Electrode on spark plug smashed closed while running

Being the other two cylinders didn't ding their plugs, then there is a problem in that hole. That engine has no head. Everything comes out the rear.

 

[Jonbmyers]

Re: Electrode on spark plug smashed closed while running

So I guess I'm probably venturing into my first rebuild of a marine engine. So if it doesn't have a head that means the carbs get removed and the pistons come out that end? This is going to be fun.

 

[quicktach]

Re: Electrode on spark plug smashed closed while running

Make sure it's not a plug problem first. Correct plugs for engine? (Don't rely on a parts man - check for correct plugs yourself!) All three plugs exactly identical ? Center plug missing ring ? Gaps on plugs identical ? All plugs torqued in equally ? Once plugs are verified OK ....then start on checking engine itself ...start with finding TDC with a dial indicator.