Yz250 crank bearing seized

Flit250
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Flit250
Edited Date/Time 2/21/2014 7:35am
Hi I ride a yamaha yz250 2008 model and I have had the left side crank bearing seized on me twice with only an hours ride each time, does anyone know why this is happening? The only thing I can think is my carb settings are out and it wants dropping down a peg so it's getting more fuel then leaning in. It has also got a fmf gold series pipe with the power core two shorty back box and pro series Boycen reeds installed so I'm thinking with this set up it needs more fuel to lube them bearings. Any ideas will be much appreciated, cheers.
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jsmx97
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jsmx97 2/17/2014 9:12am
2/17/2014 9:12am
Crankshaft out of true will cause the main bearings to fail. That would be the first thing I'd check.
Arkmx
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Arkmx 2/17/2014 10:20am
2/17/2014 10:20am Edited Date/Time 2/17/2014 10:22am
Also check your Crankshaft Seal to see if it backed out and closed off the "oil" port in the case that feeds the bearing it's oil-fuel mixture. If it did back out.... use a few drops of Red Locktite on the seal when replacing - rebuilding to hold it in place.

I have had this happen on our KX 65 before. Sucks to tear it all down, rebuild it, then it runs fro a short time and then bearing goes out again! Red Locktite was used on the seal the during the second rebuild with no more problems!

Good luck.
kijen
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kijen 2/17/2014 1:55pm
2/17/2014 1:55pm
Agree, check your jetting and your ignition side crank seal, ad a friends pretty much do the same a few hours off the showroom floor...he firt tried jetting, but a stock motor should not have tun run a 220 mj, it was the crank seal, running a 180 mj and perfect...
Flit250
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Flit250 2/18/2014 12:26pm
2/18/2014 12:26pm
Cheers guys thanks for the advice! Anything else I should check before I put her beck together? I will let you all know the outcome when I rebuild it on Saturday and ride Sunday. Cheers.

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Jakes Dad
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Jakes Dad 2/18/2014 1:18pm
2/18/2014 1:18pm
Make sure it's centered also, glad I finally bought a press, makes that chore much easier. Don't like banging on stuff with a hammer.
RMRider1
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RMRider1 2/20/2014 5:12pm
2/20/2014 5:12pm
When u install the bearings, freeze them and heat the case, they slide right in!
Flit250
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Flit250 2/21/2014 7:35am
2/21/2014 7:35am
Yes that's what I usually do is freeze the the bearings and heat the case up with a blow torch any they just drop straight in with no messing about with presses or hammers.

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