Valve cover breather hose pressure
  • Johnbeton
    Posts:10
    Joined:Sun Mar 26, 2017 2:40 pm
    Valve cover breather hose pressure

    by Johnbeton » Sun Mar 26, 2017 2:46 pm

    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
    Posts:1148
    Joined:Tue Jan 04, 2011 3:31 pm

    Re: Valve cover breather hose pressure

    by Back2-2 » Mon Mar 27, 2017 8:39 am

    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.
    Neil
    Black Hills of SD
    Life without Motorcycles would just be boring, really boring
    Honda 450X. Yamaha Tracer GT900. HD Fat Boy. Triumph Bonneville. Yamaha Majesty 400. Yamaha Grizzly. Yamaha Wolverine. Yamaha TW200
  • Johnbeton
    Posts:10
    Joined:Sun Mar 26, 2017 2:40 pm

    Re: Valve cover breather hose pressure

    by Johnbeton » Mon Mar 27, 2017 10:00 am

    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

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