What's the most likely culprit here???

[cwehse]

(98 GP1200) This is what my piston looks like, ski was running fine all day, then the power went down to only two cylinders working. Is this from running "lean?" What is the recommended repair here, should I just replace the engine and possibly the oil pump?

Should I also consider rebuilding my carbs at this time? (I was thinking that maybe they were due and I could do them while the engine was removed.

Thank in advance for advice!

[Technical Support]

Re: What's the most likely culprit here???

No one can accurately guess until you tear it down completely and show the whole piston.

[dank]

Re: What's the most likely culprit here???

Looks like you had dentonation and then a ring fail from the piston burning away and seizing. This could be the carbs not supplying enough fuel or something in the bottom end allowing too much air into the cases like the crank seal, reed gaskets, cracked intake ect.

Either way you should get a new block, rebuild the carbs and check the oil pump output during break-in or block it off and premix.

[cwehse]

Re: What's the most likely culprit here???

Yea, I definitely like the idea of replacing the block, and I'll certainly look at the other items, thanks for your help!

[bstoppelmoor]

Re: What's the most likely culprit here???

That's what my piston heads looked like in the first and second cylinder. I have installed a SBT rebuilt engine and everything went back together great! Good Luck!

[cwehse]

Re: What's the most likely culprit here???

Bstop

Did you ever figure the root cause of your piston damage?

[CTXL1200]

Re: What's the most likely culprit here???

It looks like the powervalve failed....you can see their is a chunk missing from the piston that perfectly aligns with the exhaust port..from there the broken piece just bounced around in the cylinder...

Just a guess..

[uncle-buck]

Re: What's the most likely culprit here???

The '98 GP1200 motor doesn't have power valves. He needs to tear it down far enough to show photos of the piston from several angles.

[cwehse]

Re: What's the most likely culprit here???

Yea, actually...I just went ahead and bought a rebuild from SBT and I am currently installing it, I spoke with the TS (Bryan) while I was there and he was fairly certain it was carb related (running lean), I am currently do a carb rebuild simultaneously.

CTXL1200 - You are correct in the fact that the piston seized and a piece broke off corresponding to the exhaust port, it is not a pv 1200 though, and thus I'm going with the carb theory...

Interestingly enough the carb associated with that cylinder looked mint when I tore it down, but the center carb was gunked up??? So ... I have no idea...

[dav_dman]

Re: What's the most likely culprit here???

what did the chk valves in the fuel pump on that carb look like? Internal filter? Put the oil pump on a drill and make sure it's pumping...each oil line has a chk valve too...might wanna soak em.

[cwehse]

Re: What's the most likely culprit here???

Thanks for your reply...The carb on that cylinder was mint. In fact, muct better condition that the other 2 carbs when I rebuilt them all afterwards, one of the other carbs had blatant creases on the check valves, and those cylinders were fine. I will try to figure out how to do that oil pump check you're talking about. I think the ski may have been really low on gas at the time it happened, and cause the carb furthest from the tank to run lean...That possible?