Why do I keep losing the #2 piston??

I rebuilt my 1987 125 due to a bad piston/bearings. And it has gone bad again after 5 minutes of running. So what do you think the problem is? I only have problems with that piston...the others look good. It looks like it is running extremely lean. The motor locks up after running at full throttle. It has little dropplets of water in that cylinder. Any ideas?

Could it be the reeds? They didn't look bad but...hmmm. If it was the top carb one would think both 1 and 2 would be bad. What should I do?

Thanks,
Curtis

Re: Why do I keep losing the #2 piston??

I would say a head gasket or crack letting water in and the water is entering in an area that it rinses away the oil.Any evidence that the damage is in the same spot each time?

Re: Why do I keep losing the #2 piston??

The head gasket looks perfect, but it has only 15 minutes run time on it. (10 of that is idling) I just can't believe that water is getting in. That cylinder has a new sleeve, but the block was not decked....that is the next step. I am going to rebuild the carbs, and replace the reed petals, hopefully that will solve the problem.

Re: Why do I keep losing the #2 piston??

I already ordered the Boyeson reeds. I just thought it might be good insurance. I can't decide what the problem is! I was told by one guy that he runs the motor for 1-2 hours on the hose before he takes it to the lake. Then he only runs at partial throttle for the next 3-5 hours. I have all new wiseco pistons, and all I did was run it about 10 minutes, then out to the lake for a wide open run. Could it be that I just didn't give the forged pistons time to break in? I am going to back the timing off 3-4 degrees, and confirm that I have good water flow, clean the carbs, and test the overtemp sensor circuit. Maybe I was just too hard on it too fast.

Re: Why do I keep losing the #2 piston??

Normal process after re-sleeving is to deck the block. Was there evidence of water in that cylinder before the re-build? If not, then I would guess that decking the block may fix the water leak.

Also, after the re-build did you use double the oil? This is standard practice until the motor is broken in. I had a similar experience years ago. I didn't use double the oil, took it out on the lake and opened it up after only about 30 minutes running after a new re-build and scored two pistons on a 1988 125HP motor. Had to replace those two pistons (Weisco brand)/rings. Luckily honing cylinder and replacing pistons and rings did the job.

Re: Why do I keep losing the #2 piston??

I did not deck the block the first time.....but I did after having that cylinder re-bored .020 over. I did not see any evidence of water at the head. I have come to the conclusion that I just went to full throttle to soon. The machinist seems to think it overheated, so I will pay close attention to that as well. I did use double oil, with 91 octane fuel. I will give it 4-5 hours before going to full throttle. I may even take the head off and inspect the cylinder after about 10-15 minutes. It's just odd that it was only one cylinder/piston.