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
