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Crankcase venting

Discussion in 'The Garage' started by Gator xs2, Jul 9, 2019.

  1. 5twins

    5twins XS650 Guru Top Contributor

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    A big part of the problem on the early models (besides too much oil) was that Yamaha made the breather outlets too big. Through the '70s, they tried several "fixes". First one was to cap one outlet off completely and only use the other one. Next try was going back to the 2 outlets but with rubber reducer plugs fitted into them. Finally, they redesigned the breather housing, changing it to a single outlet with a very small hole in it. You can retrofit this late style single pipe breather housing to your early bike if you like.

    [​IMG]
     
    Gator xs2 and gggGary like this.
  2. Mailman

    Mailman Hardly a Guru Top Contributor

    I wouldn’t mind having one of those single outlets myself, just for simplicity.

    Or? A little size reduction?
    0BB8AF89-A0F4-4AE2-B21D-C4E27CD74D5B.jpeg
     
    Gator xs2 and gggGary like this.
  3. Gator xs2

    Gator xs2 XS650 Addict

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    I knew there was a reason you did that!
     
    Mailman likes this.
  4. Gator xs2

    Gator xs2 XS650 Addict

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    That’s the same article I read. Who knew?
     
  5. Mailman

    Mailman Hardly a Guru Top Contributor

    solo2racr likes this.
  6. barncat

    barncat XS650 Addict

    Well, this is a subject I'd never given much thought to- I just assumed Yamaha engineers knew what they were doing when venting to outside air on the early motors, and getting some chain lube in the process. They do mist a significant amount of oil.

    These brake check valves must be rubber diaphragms or reed valves? I have to confess i don't see how they are supposed to restrict oil loss if they still communicate with outside air...
     
  7. 5twins

    5twins XS650 Guru Top Contributor

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    They only let air out and not back in, and this creates a slight vacuum in the case. I guess that's what keeps the excess misting down. I started out using a small K&N filter on the end of my open breather hose. I had removed the rubber restriction plugs following a tip from another web site. That turned out to be a mistake. The filter was always very wet with oil. I put the plugs back in and switched to the power brake check valves. I've never seen any oil come out of them. Their outlets are, at the very most, just a little damp with oil.
     
    Mailman likes this.
  8. barncat

    barncat XS650 Addict

    Noted.

    From what i can find these valves are just spring loaded plungers. I'm pretty surprised if they're holding up to millions of cycles over time. They'd ordinarily see orders of magnitude less as brake parts.
     

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