1998 mercury 90HP question

[CRISCO]

Hello,

I have a 98 mercury 90hp, I just installed new ngk BUHW-2 spark plugs a couple of weeks ago. I was checking the plugs to make sure everything was good to go and noticed the spark plug coating on the top cyinder was cracked. I replaced the plug with a new and ran the boat for about 4 hours while trolling and it was cracked again. The guy at advance auto told me the reason for the cracking was they were installed to tight. I installed the second plug with my hand never used a wrench and that one was cracked. I was wondering if anyone out there could help figure out was going on. thanks

 

[Bondo]

Re: 1998 mercury 90HP question

Ayuh,... Where,.. Exactly, are they cracking,..??

 

[verado7]

Re: 1998 mercury 90HP question

sounds like detonation - check compression on all cylinders and compare - you could try using higher octane fuel - timing overadvanced but that should cause it on all cylinders - that 1 cylinder is getting too hot - leanfuel mix in the cylinder ( bad reeds ) even excessive carbon can all cause this -