2002 Yamaha dt125r
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I have recently rebuilt my dt125r engine, the engine was running fine when doing the heat cycles, I ran the engine on idle until up to running temperature and then waited until it was cool before running it again. I repeated this 5 times before riding the bike. It was running fine for approximately 2 miles and then the engine made a high pitched sound and then locked up. On inspection I found the mains bearings had failed. Any advice on what would cause this or any advice on what I have done wrong. I replaced all bearings and seals with koyo bearings that were brought from eBay. Anyone else had this problem or any advice would be greatly appreciated
Mikey
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I have recently rebuilt my dt125r engine, the engine was running fine when doing the heat cycles, I ran the engine on idle until up to running temperature and then waited until it was cool before running it again. I repeated this 5 times before riding the bike. It was running fine for approximately 2 miles and then the engine made a high pitched sound and then locked up. On inspection I found the mains bearings had failed. Any advice on what would cause this or any advice on what I have done wrong. I replaced all bearings and seals with koyo bearings that were brought from eBay. Anyone else had this problem or any advice would be greatly appreciated
@mjmikey Koyo bearings are very good quality but did you order the correct ones for this application? I believe for crankshaft applications they need to have larger clearances to allow for heat expansion; PJME refer to this as "the correct R1 type" but I've also heard it referred to as C3/C4 clearance:
https://www.pjme.co.uk/acatalog/Yamaha-DT125LC-Crankshaft-Main-Bearing-RH-5698.html#SID=103
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dont buy from ebay. buy from pjme.
the bearings shouldnt of failed. were you running it in or caning it? did you make sure only to use the outer edge of the bearing to drift it in? if you pressed against the centre race it could of distorted, even dented the balls giving it a very knoychy feel...
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