What may have caused this damage to the piston

Hi,

I recently inherited a 2004 RM250 that does not start. I took it apart and the piston has some serious ring damage. I think it was caused by damage to the cylinder which caused the rings to get stuck and break apart. I am sending the cylinder to Powerseal for repair and replacing the crankshaft, but is there any thing else that may have caused this that I need to check into before reassembly and running it. So it does not happen again? THANKS!

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Looks like detonation to me. Check the jetting before you fire up your newly rebuilt engine and use some good fuel.

How does the head look?

could be the big eng rod bearing coming apart and damaging the piston. also clean out the exhaust pipe.

How does the head look?

The head looks the same as the piston, mangled with ring pieces buried in it

Pissed & broke. (piston broke...:smirk:)

Well thats my joke for the day....

Ring snagged on the exhaust port or whatever. After that it's just jingly jangly all the way to the bank.

Set the end gaps on rebuild and send the piston to the machine shop to get the correct piston/bore clearance.

I would check the bottom-end this does not look good.

Looks like detonation to me. Check the jetting before you fire up your newly rebuilt engine and use some good fuel.

Really :smirk:

I would check the bottom-end this does not look good.

I am replacing the crankshaft and have already removed the old one....I think the problem started in the top end, and then filled the bottom end with a lot of ring pieces and shavings

Pissed & broke. (piston broke...:smirk:)

Well thats my joke for the day....

Ring snagged on the exhaust port or whatever. After that it's just jingly jangly all the way to the bank.

Set the end gaps on rebuild and send the piston to the machine shop to get the correct piston/bore clearance.

That is what I am guessing as well....just don't want any recurrence after fixing the bottom end and cylinder

I've done that, in my case it was the rod/crank bearing that died. It was a long and hard battle but ultimately the bearing just couldn't take it anymore.

In your case it's one or both of the rod bearings, how's the wrist pin bearing look? Splitting the cases and replacing the crank with a rebuilt one is an excellent idea. Be sure to replace the wrist pin bearing and both main bearings too. And like someone else already mentioned, CLEAN EVERYTHING! With that much metal floating around who knows where it all is (the pipe, the ports, crank case lube vents, etc.) you get the idea.

I've done that, in my case it was the rod/crank bearing that died. It was a long and hard battle but ultimately the bearing just couldn't take it anymore.

In your case it's one or both of the rod bearings, how's the wrist pin bearing look? Splitting the cases and replacing the crank with a rebuilt one is an excellent idea. Be sure to replace the wrist pin bearing and both main bearings too. And like someone else already mentioned, CLEAN EVERYTHING! With that much metal floating around who knows where it all is (the pipe, the ports, crank case lube vents, etc.) you get the idea.

Cleanliness is next to Godliness!! And it's also required on dirt bike rebuilds too!

Cleanliness is next to Godliness!! And it's also required on dirt bike rebuilds too!

What he said! :smirk:

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