2008 crf450 oil coming out of overflow tube!!

mxryder231
Posts
70
Joined
6/24/2008
Location
San Marcos, CA US
7/25/2011 3:49pm Edited Date/Time 1/27/2012 4:52pm
so he recently had a top end done on his crf450r. its a 2008 model, and i know of the oil seal that separates the tranny from the engine side of the motor, it is not transferring the oil from one side to the other. its coming out of the valve cover and he recently took the stock plumbing off in favor of the Tokyo mods valve hose which just routes it to atmosphere. because he is getting a lot of engine oil coming out of the valve cover to the air box. my question is what could cause this. i know on my Yamaha it spits out a little bit, but his is causing the engine oil level to go below the site glass on the engine side. could it be a crank seal? any input would be great..
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lumpy790
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9/18/2007
Location
York, SC US
7/25/2011 6:45pm
How is "his " bike being ridden?
mxryder231
Posts
70
Joined
6/24/2008
Location
San Marcos, CA US
7/25/2011 7:50pm
He is a beginner/novice he could run novice but he has not raced. It started doing it after the top end rebuild
7/25/2011 9:23pm Edited Date/Time 7/25/2011 9:25pm
Four strokes tend to push oil out of the breather when there is excess crank case pressure. Sounds like there is some blow by getting into the crank case.

How was the cylinder condition? Was the taper from top to bottom measured? Was the bore deglazed / light honed for the new rings to seat properly? Ring end gap measurement spec out OK? Piston clearance in spec?

Sometimes you can get away with just opening the boxes and installing new parts. But not always. That is why there are spec's in the service manuals. May have to pull it back down and re-measure things.
lumpy790
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9140
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9/18/2007
Location
York, SC US
7/26/2011 6:05am Edited Date/Time 7/26/2011 6:11am
MX/Off doad only?

Blow by is a problem in supermoto and road racing MX singles.

Who did the rebuild? Were the rings aligned properly?

The Shop

mxryder231
Posts
70
Joined
6/24/2008
Location
San Marcos, CA US
7/26/2011 7:54am
the cylinder looked good good cross hatch. it was not measured. the end gap was. the piston rings and piston were stock parts from honda. he rides mainly motocross. he has a buddy who is a mechanic who did it.

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