2c leak down test
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Thread: 2c leak down test

  1. #1
    Member #
    Join Date
    Jan 2014

    2c leak down test

    Hi. Further to my previous post about leak testing . I blocked up the exhaust ports with some old inner tube rubber.
    I cut out a short length of inner tube with the valve in it and fixed this onto one inlet stub with a jubilee clip. Similarly I blocked the other inlet with tube. I pumped about 7 psi into the valve. The tube over the other inlet expanded, which I take to mean the labarynth seal is leaking. The pressure slowly leaked out over a few minutes so I'm thinking my crank seals are leaking a bit, or potentially I'm losing pressure into the gearbox. I sprayed soapy water on joins to find leaks in my kit.
    So, what if anything have I proved ? Any thoughts guys?

  2. #2
    Senior Member
    Mark Hollingsworth
    Member #
    Join Date
    Nov 2008
    Port Angeles, WA USA
    If you have no leaks in your testing setup- then crank seals are the most likely.
    Pop off the flywheel and listen for a leak- then use soapy water.
    If no leaks there, then check the clutch side (more work). When I’ve seen the clutch side fail, generally the bike will smoke (burning gearbox oil) and have a much different smell.

    of course you want to check for a leaky sparking plug seal, head and base gaskets too.

    I’ve had several bikes personally in that vintage that had crank seals quite bad.
    Of course, with a twin- you generally have seals on the inside (between cylinders) and those are much, much more difficult to test. I have a manual here someplace, but I think it does have seals there.

    I just checked the parts book.
    it has a seal of some sort between (looks like an ‘O’ ring). Oddly, they call the seals ‘junk rings’.
    Last edited by Lotus54; 05-21-2019 at 08:13 AM.
    ron d likes this.


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