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'05 CRF250r Blowing Oil Out of Crancase Top Vent

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OK Guys. My son has a 2005 CRF250r (freshly rebuilt) which runs great but is overfilling the crankcase with oil, emptying the transmission and blowing the oil out of the top crankcase vent (the one that connects to the cam cover).

What is the cause of this? It ran fine, with no problems, for 30 or 40 hours, post rebuild. Suddenly, it starts intermittently sucking all of the oil from the tranny, into the crankcase, and blowing it out the top vent tube. FREAKY!

Someone please help.

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The right crankshaft seal or the balance shaft seal is bad. One of these 2 items are usually the culprit. Replace them both and you should be fine. The reason it's pumping out of the overflow is because it's over filled and it has to go somewhere. Easy fix.

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Those two seals, bad or flipped and are facing the wrong way. I got a 450 motor now that does exactly the same thing, and sure enough there's what looks like a brand new balancer seal with the spring side facing out. AFAIR you'll need clutch side gasket, some coins or gear holder, nice to have a clutch holder tool as well.

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OK. I removed the side cover and replaced the crank seal. There was no obvious damage to the crank seal. The balancer seal is not accessable from this point. The bearing is on the outside. The seal is on the inside of the case. I am going to refill the oil and give it another try. Does anyone have any other ideas?

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