92' Merc 200 Burning pistons

[Kenny Bush]

Can anyone out there tell why I am burning pistons. I have a carb'd 92' mercury 200 with extra long shaft. The motor has less than 50 total hours on it. I bought it with no compression in #1 and #2. When I tore into it, I found that the piston tops were melting away. I replaced pistons 1 and 2 and proceeded with breakin. After about 15 hours of double oil breakin, number 3 is dropping compression. Pulled head and found #3 is melting away. When I rebuilt it the 1st time, the timing was way advanced but corrected it to factory specs. Now after 15 hours #3 is coming apart. All my plugs are oily and I have not even showered down on this motor yet. Could it be ignition? The timing is on the money.

 

[trevorcday]

Re: 92' Merc 200 Burning pistons

The first thing to look at is carbeuretors. A blocked main jet will lean out the mixture and cause a piston to burn. In my experience, though, ignition is a more likely culprit. One thing you can try is to index the flywheel and check timing on each of the 6 cylinders rather than just #1. If the timing is advanced or erratic it can raise the combustion temp's enough to melt pistons.<br /><br />These are always tricky problems to troubleshoot. Good Luck.