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signs that the main bearings are going?

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what are the signs that the main bearings are starting to fail? and what can happen if you ride them till they die?

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Sometimes they start to make a 'howling' or 'whirring' type sound when tehy get pitted and sometimes they make no noise and just go BOOM.

If you pull off the flywheel and feel ANY U,D,L,R play in the crank then your bearings are toast.

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Sometimes they start to make a 'howling' or 'whirring' type sound when tehy get pitted and sometimes they make no noise and just go BOOM.

If you pull off the flywheel and feel ANY U,D,L,R play in the crank then your bearings are toast.

Can you do this test just leaving the flywheel on?

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what are the signs that the main bearings are starting to fail? and what can happen if you ride them till they die?

dont know of any signs or symptoms. Wish I did. Just lost a main on an kx85 with only 10 hours on it. When it let go,sounded like gravel in the crank case, but still ran. It did not break things up badly, but the skirt of the piston was scored, and had to be replaced

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Can you do this test just leaving the flywheel on?

I think PC meant to write flywheel cover. Yes just grab the flywheel and see if there is an loose motion.

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I think PC meant to write flywheel cover. Yes just grab the flywheel and see if there is an loose motion.

Yes.

thanks for correcting :worthy:

I replace my mains and rebuild (or replace) the crank every 200hrs whether its showing any signs of failing or not. Especially since I have head work and dont have much room for error when the piston is at TDC.

At 200hrs the main bearings are probably okay, but the con rod bearing and seals are usually tired. Since the cases are already split there's no reason not to replace the mains when you're in there IMO.

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well it feels like my main bearings get tight when i spin the crank, and recently i messed up my cylinder, head, and piston due to some metal coming from somewhere. thing is im not sure if its foreign or not, and before that happened my bike wasn't idling very well and it bogged on top end which it never did before. so it kinds to lead me to bealive its something from a bearing because it sticks to a magnet...

sorry for the rant but i need to figure out whats going on, i know next step is to split the cases... again :worthy:

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