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So here's where Im at 05 crf 450r had a complete top and bottom end rebuild done on my bike back in March. Broke the motor in properly, changed the oil, and then took it out to Glamis in april put 2hrs on the bike went on a long ride I came back and oil was running out of the air box I passed it off as I had dumped the bike over and oil got in to the air box and just took a while to seep through my air filter. checked the oil on the engine and it looked good it never crossed my mind to check the tranny side. Long story short I went on another ride the next morning got about 15 minutes into it and heard a high pitch winding sound coming from the bottom end and appears to be coming from the tranny got my bike back to camp and did a more thorough inspection and found my engine side of the bike was excessively full and the transmission side was bone dry. I think the noise I heard was the bearings in the transmission being burned up due to lack of lubrication? But what would cause a loss of oil in the trans side,and it to be sucked into the motor side? Has this happened to anyone? Its been sitting in my trailer all summer. I've Been busy with work so just now getting around to having time to get my bike fixed. Any help or insight would be greatly appreciated.

Refer to this post , it shows the parts and gives a brief explanation of the fix , its the right crankshaft seal , also make sure the vent line for the transmission is clear , as it can cause a buildup of crankcase pressure and cause oil to blow out , or migrate

http://www.crfsonly.com/forum/viewtopic ... kcase+seal


It does happen , though not everyone has to deal with it

i had the same thing happen to my 450x i had just done the bottom end myself n silly me put the right crank seal in backwards so all the oil got sucked into the crankcase fortunately for me i noticed it fairly quick n stopped so no damage was done n was just a matter of removing the right side cover and replacing the seal again so far so good