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OK, here is what happened. My brother bought a used XTM .21 (1st version) on the cheep while on vacation in WV and gave it to me for some painting work. I put it on my Hyper 8 and it ran like a scolded dog. That is till the filter came off and I sucked a bunch of track through the carb.

The piston and liner are done. I have found replacements but also discovered during tear down last night that the crank will spin inside the main bearing. The bearing is not locked up, it just allows the crank to spins sometimes while the bearing stays put.

Is this normal for nitro engines or is it a problem?

sounds to me like the crank is shot too.

unfortuntley thats a problem.

I suspect the crank has worn in the bearing seat.

ie where the bearing sits on the crank.

ed

Well, it was fun while it lasted. Looks like I got another paper weight for work. I'm not machining on this one when you can buy a nice engine for $150.