Bmw r75/5 leak down test

Discussion in 'Airheads' started by Telo, Apr 21, 2014.

  1. Telo

    Telo Adventurer

    Joined:
    Sep 28, 2013
    Oddometer:
    38
    Location:
    Clifton NJ
    Hey yall, so I did a compression test today got some bad news. Right cylinder has a max of 96psi and the left cylinder has a max of 100psi.

    Bought a leak down tester from harbor freights. I know that it only works at 15psi but, I was getting stable readings. Right cylinder had a 33% leakage and the left cylinder had 16%.

    At 15 psi, i thought it would be hard to here air escaping but it was quite noticeable. Both cylinders were leaking air from the oil filler. I figured it must be rings.

    Strange thing is, when i stick my finger in the intake port, i feel a coating of oil, more noticeable on the right cylinder. Could this be from the breather hose caused by excessive blow-by? Would bad valve guides cause oil to pass through the valve stems? From the leak down test, i couldn't here any air escaping past the valves, even when i bumped the psi to 50, only air can be heard from the oil filler.

    Im no professional, but from my guess, with the information i gathered, it seems i need rings. Any one care to have a thought? Second opinion would be great! :ear
    #1
  2. Big Bamboo

    Big Bamboo Aircooled & Sunbaked

    Joined:
    Sep 29, 2010
    Oddometer:
    8,320
    Location:
    Big Island of Hawaii
    Just to confirm; you did the compression test with the carbs removed or the intake tubes removed and the slide held open. Yes? Oil in the intake tube is from the breather. If the blow by is really bad you will foul the spark plug on that side in no time...
    #2
  3. Telo

    Telo Adventurer

    Joined:
    Sep 28, 2013
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    Location:
    Clifton NJ
    the carbs were removed
    #3
  4. supershaft

    supershaft because I can

    Joined:
    Sep 9, 2010
    Oddometer:
    9,116
    Location:
    San Francisco Bay area
    No need to remove the carbs to do a leak down test.

    I have no experience leaking down at 15ftlbs. It sounds wrong to me. The FAA does it at 80ftlbs and everyone else at 100. Snap-On made one that did it at 60ftlbs. That works I know.

    The percentages mean very little compared to where it is leaking from and to determine that takes some experienced listening. But first: Was the bike on it's side stand in the last 50 miles? If so, that will throw off your test. If not, listen to where it is leaking from. If either valve is leaking at all, you don't know how much your rings are leaking. IF your valves are not leaking, do a normal compression test. If the bad cylinder tests normal, you probably have lined up ring gaps.

    Under 5% past the rings is real good. ANY amount leaking past a valve is not good. Less than 1% past a valve will effect idle if nothing else except get worse.

    You will hear/feel air coming out of the crankcase even with under 1% leakage. Ring gaps do that.

    Good luck!
    #4
  5. Telo

    Telo Adventurer

    Joined:
    Sep 28, 2013
    Oddometer:
    38
    Location:
    Clifton NJ
    the bike was not on its side stand
    #5