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main bearing failures on 06 RM250

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JUst wondering how many have ever experienced main bearing failures on RM250's? I lost my first one ever yeaterday during a harescramble race of all places. Just heard a weird screaming noise and then a rear wheel lockup. Thought it might be a siezed piston at first although it did not sound that way. Disassembled today and it was the clutch side main bearing. It looked a little dry but the ratio was same as always at 32 to 1 Bel Ray.

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Thats a good question. I bought the bike used a little over a year ago. The top end looked good with the exception of a slight crack in part of the piston skirt on the intake side. But two of the balls were missing out of the clutch side main. I don't know where they went , but they did no damage when they left. The bearing retainers broke because the bearing was stuck to the crankshaft.

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A cracked piston could shatter any second when run. Never run a piston with a crack. Besides that, if the bottom end had never been replaced it could have had hundreds of hours on it and was bound to fail eventually. In this case it wasn't the bike's design at fault, just the previous owner's lack of maintenance.

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Upon further inspection I now believe that someone may have damaged the main bearing when they installed it. The left side was in very good condition.

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