Burnt piston

[tsludwig]

I recently bought a 95 GTX 650 that was only running on one piston. I found no compression in the front cylinder. I pulled the top half down and found the piston coming apart on the front cylinder and the piston looked fine on the back. You could see witness marks on the top of the piston where parts of the ring got up there and were banging around. I've worked on 2 cycles before that went lean and burnt a piston before but there were not signs of a lean condition on this motor . The plug looked brown, the top of the piston was damaged but did not look white. I bought a top engine kit, honed both cylinders and replaced both pistons. It started and ran great but after about 15-20 minutes it started running on one cylinder. Checked compression and again none on the front. Same thing started happening, pieces of the ring came apart and got on top of the piston.
My question is, does the oil injection feed each carb independently and if so could I have a lack of oil to one cylinder or do you think it's a lean condition?
Any help is appreciated. Thanks

[1fastski.com]

Re: Burnt piston

you need to check for an air leak or clogged carb and check the oil lines they crack over time .

[dsolie]

Re: Burnt piston

Did you double check the lower end for debirs from the first meltdown? You might have had some material left in the cases work it's way back up too.

[Bill O'Neal2]

Re: Burnt piston

I think you should have rebuilt those carbs, as you should ALWAYS rebuild or at least clean and test a set of carbs before installing them onto any motor that is new or has a new top end.
But, that may not be your problem at all in this case. You might have crankshaft bearings coming apart or you might have left debris in there from the last broken piston or bearing.
When a motor gets no oil to one clyinder or the other, the pistons will look siezed, greyish in color like graphite has been sprayed on them, as well as the clyinder walls and even the head dome. Sometimes they will "look" like the clyinder was running plenty rich, but what would you expect if the rings are broken or stuck ? all that fuel and oil has to go somewhere, as it will not be compressed and all of it ignited and burnt off.
You best take that whole motor apart, it could have a leaky seal, broken bearing, cracked intake, clogged up carbs or any number of problems.

[tsludwig]

Re: Burnt piston

Did you double check the lower end for debirs from the first meltdown? You might have had some material left in the cases work it's way back up too.

I thought of that and looked very closely at the crank, didn't see any witness marks on the crank or see any pieces in the bottom of the crankcase.

[Bill O'Neal2]

Re: Burnt piston

Oh how many times I have heard that story ! Without running a small magnet through there, it is VERY possible you did not see the debris. Why? because you cannot always see it and it doesn't leave any marks either..

[tsludwig]

Re: Burnt piston

Oh how many times I have heard that story ! Without running a small magnet through there, it is VERY possible you did not see the debris. Why? because you cannot always see it and it doesn't leave any marks either..

I will give it another check tonight. Thanks.