Breather tube

3 replies to this topic
  • Jandre visagie

Posted August 31, 2016 - 02:54 AM


Good day. I have a yamaha yz450f that i have bought 2 weeks ago. While i was riding i saw gas coming out of the breather tube. Can it be of the high compression of these 4 stroke machines or because of worn rings on the piston ? Will the bike not use oil when its rings are worn ? Because this bike is fantastic and still has a lot of power so must i be worried because of the gas that is coming out from the breather tube ? I also have a WR 450 '06 thats breather tube goes into the airbox but he doesnt breath as far as im concerned. Help me please i dont now if i must be worried or not.

  • grayracer513

Posted August 31, 2016 - 06:24 AM


Normal.  The piston has a top and a bottom, and as it goes up and down, it displaces 450cc of air on both sides; in the cylinder and in the crankcase.  That air, and the pressure from combustion that leaks past the rings needs to be allowed to move in and out of the crankcase so pressure doesn't build and force out seals.  Your WR does the same thing, whether you've ever noticed it or not. 


It can be a matter of concern if it becomes excessive, because that indicates the rings are leaking more than they should. 

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  • Jandre visagie

Posted August 31, 2016 - 10:29 PM


Okay thank you. So i dont have to worry and just enjoy my bike ?

  • Jandre visagie

Posted August 31, 2016 - 10:48 PM


Hiw do i know when it leaks more then it should ?

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