Interpreting Leakdown Test Results

Discussion in 'Motorbike Technical Discussion' started by Manjo, Sep 27, 2005.

  1. Manjo

    Manjo Guest

    I've got a Kawasaki 1995 vulcan 1500 V-Twin that has been running rough
    on uphills/accelerations.

    I've done a leakdown test ont he bike and have a few questions I'd
    llike to pose to the group for their comments/help to interpret.

    The leak is 20%. Last year the leak was 15%. I fully suspect the leak
    will be 25% next year. I feel it's time for a top end job. Is this
    the right decision? I'll have all winter to do the job myself. Any
    tips or suggestions would be welcome.

    I had weird results that I think are my problem with getting the
    cylinder to TDC. Aft3er positioning the cylinder and putting the bike
    in gear, I connected the gauge. Teh leak gauge went directly to 90%
    leak. As the compressor cycled on to refill the tank, the gauge needle
    started to climb, then a slow whoosh of air would come out of the carb
    intake filter, the needle dropped down, stopped, then it began to
    climb, again. This cycle went on several times until the leak gauge
    needle finally climbed to and stayed at a steady 20% leak. I could
    then hear the leak through the oil filler orifice identifying the leak
    (I think) as the piston rings.

    I have a couple of questions about this: did I position the cylinder
    just on the edge of the intake cycle and the pressure build-up finally
    allowed the pressured air to escape around the valve? Or, would a
    cracked piston ring somehow have these same symptoms?? TIA for any
    help here.

    Manjo 1500A9 Kawa Vulcan
    Manjo, Sep 27, 2005
    1. Advertisements

  2. Does the engine smoke for about 30 seconds or a minute on startup, then
    quit smoking? Does the engine use oil with no apparent smoking while
    you're cruising along the highway? Are you getting tired of adding a
    quart of oil every 500 miles or less?

    Bad valve guide oil seals would cause this. The intake valve won't seat
    properly once a lot of crud builds up on it. It might even burn. And,
    perhaps excess oil from the worn valve guide oil seals might make the
    piston rings stick.

    That scenario would satisfy the description where air pressure
    apparently shoved the intake valve closed, and you still heard leaking
    past the piston rings. (1)

    In order to get a good seal from the piston rings, spring tension has
    nothing to do with it, air has to get behind the rings and push them
    outward. So, if the piston ring grooves are full of carburized oil,
    making the rings stick, that might be what's causing your compression

    Have you tried anything like Rislone to free the rings? And Techron
    Concentrate might clean deposits off the valve heads. It won't replace
    the valve guide oil seals, if that's what the problem is.

    (1) Or, does that engine just have hydraulic lifters and they are
    krusty kritter, Sep 28, 2005
    1. Advertisements

  3. Manjo

    Manjo Guest

    The top end has about 80k miles after piston replacement to cure piston
    slap, something this model year has too often.

    Yes, there are hydraulic lifters; I agree it could very well be the
    valve guides, too;

    Regarding the piston rings, we were on a long ride this summer and
    after the first few 300+ miles per day, I had to ADD a quart of oil.
    Then oil consumption almost went way entirely. I suspect the hard
    riding and the addition of Sea Foam to the fuel, freed-up the rings.

    When accelerating, especially when going up hill, the engine runs
    rough, but strong. I've replaced the spark plug wires, and have a set
    of ignition coils to test with to eliminate a spark problem. But I
    tend to agree strongly with your opinion: it's tiime for a complete
    top-end job to replace the guides, lifters,a nd valves.

    I really like the bike and have it set-up for long distance riding. I
    get about 40 miles per gallon on a good run. I want to get as close to
    50 mpg. I think a top-end job will get me there, I hope.

    Thanks for your post. It's been ery helpful. Any additonal comments
    or tips would be welcomed.

    check twice, ride safe,

    Manjo, Sep 28, 2005
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.