1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

1974/850: Too much oil out from the breather oil tank

Discussion in 'Norton Commando Motorcycles (Classic)' started by pierodn, May 20, 2018.

  1. pierodn

    pierodn

    Joined:
    Nov 10, 2012
    Hi.
    From the breather hose of the oil tank that goes free under the land near the central stand, go out a lot of oil even if the bike is running than on the stand.
    What it mean and why?
    Seems to me that there is to much oil that returns in the oil tank .
    The bike has on 2,6 litre of 20/50 oil, not more.
    Thank you.
    Piero
     
    Tags:
  2. kommando

    kommando

    Joined:
    May 7, 2005
    Sounds like it could be blowby as per your other bike.

    Blowby, combustion chamber air forcing past the rings and going into the crankcase. Could also come past the guides into the Rockerbox.
     
  3. eskasteve

    eskasteve VIP MEMBER

    Joined:
    Sep 24, 2012
    Make sure that your oil lines are correct. I had the same problem when I first bought my current bike. The previous owner had reversed the crankcase/engine breather and oil tank breather hoses at the oil tank connecting spigots. The oil tank breather on your bike may not be plumbed into the air filter housing as a number of owners will route it into a catch bottle or out the back of the bike. Here's a diagram from the Old Britts web site.

    [​IMG]
     
  4. pierodn

    pierodn

    Joined:
    Nov 10, 2012
    Hi.
    Thank you.
    So there is too much clearance from piston and barrells?
    Please let me inderstand it better.
    Thank you.
    Piero
     
  5. kommando

    kommando

    Joined:
    May 7, 2005
    Yes if the rings are worn or lost their springiness then as the engine fires the gases can escape past the rings into the crankcase and pressurise it which then shows at the breather.
     
  6. pierodn

    pierodn

    Joined:
    Nov 10, 2012
    Thank you to all.
    Ciao
    Piero
     
    Last edited: May 20, 2018
  7. Mr. Rick

    Mr. Rick VIP MEMBER

    Joined:
    Feb 6, 2009
    With the engine warm, and recently stopped, you can take a reading on the dipstick in the oil tank.
    On my bike, I must keep the oil level near the bottom line. If I put more in, it begins to push oil out the breather tube.
     
  8. mdt-son

    mdt-son

    Joined:
    Jan 19, 2012
    How do you explain that? A froathing phenomen? Maybe you have a problem with overpressure in your oil tank? There should be ambient pressure above the oil level, no matter if at the minimum or maximum mark of the dipstick.

    -Knut
     
  9. franko

    franko VIP MEMBER

    Joined:
    Dec 29, 2013
    Some of the dip sticks were marked about a half inch too high.
     
  10. pierodn

    pierodn

    Joined:
    Nov 10, 2012
    Hi.
    Could be a good idea to fit another breather, the Jim Comstock sump breather, to reduce the over oil pression?.
    In any case, the oil spray out a lot from the return pipe and from the oil tank breather pipe.
    But the bike doesnt smoke from silencers.
    Thank you.
    Piero
     
  11. pierodn

    pierodn

    Joined:
    Nov 10, 2012
    Hi.
    What about Pressure Relief valve?
    Piero
     

Share This Page

Loading...