[Johnbeton]

Hello,

I just finished rebuilding my '05 crf450 engine, and when cranking it slowly with the kickstarter, I notice air pressure comming out of the valve cover breather hose.
Is this normal, I never noticed this before, or are my valve stem seals not sealing ?

Thanks

[Back2-2]

You will always have some air escaping the valve cover due to crank case pressure that must be relieved. It is possible that from the engine sump being dry for the rebuild that you are getting a little more pressure developing ? As the piston strokes and back pressures the case it could be coming up through oil ports that have not filled from priming yet ?

Just some thoughts for you.

[Johnbeton]

Thanks a lot for this info, it makes sense what you say.
I didn't fill the engine with oil yet untill I was sure everything is ok, I'm going to fill it to spec and see from there