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Thread: Leak Down Test

  1. #1
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    Leak Down Test

    Morning all, finally got to checking the drop on power head i picked up in October. Last night i did a leak down test, just wondering why there is a fairly consistent difference from port side to starboard? i will list them in order, 1-3-5 then 2-4-6.
    Click image for larger version. 

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  2. #2
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    My opinions on leakdown testing procedure are a little different than most,and render the most accurate results,again my opinion.Most folks follow the directions and put the piston at top dead...where there's no wear,and usually get low leakdown results accordingly.A poor mans leakdown test is really better,and is faster,cheaper,and easier...do a comp check,just write down the compression numbers,squirt a couple shots of 30 wt oil in each cylinder,spin the motor over a few seconds and recheck the compression...the amount the compression goes up will be close to overall leakdown percents.
    Now my way.Follow the normal procedure but instead of locking the flywheel near tdc,pull the motor from ports open to tdc on every cylinder,stopping at several spots along the way,and look at the resulting leakdown along the working stroke of the cylinder.
    We do this with a ratchet on the flywheel nut,with a long bolted in place tube extention on the ratchet handle...(3 foot long,specificly for this task).
    DO NOT USE A BREAKER BAR for this job...when you pull the piston over tdc the 40-50 pounds of pull required will turn to push and may DE-BRAIN you...the ratchet will allow the flywheel to spin to to open the ports.
    This procedure will locate bulged cylinders,scoring above the ports etc.,that a locked flywheel
    test won't know about.
    Also,for the most accurate results check the port side of a "v" motor by pulling the flywheel clockwise,and the starboard counterclockwise to place the piston in its thrust position.I test
    at 75 lbs.
    I figure if you're going to test you might as well get the best results you can,I should'nt have to tell you to keep fingers clear,and be careful,as the flywheel is going to spin as it goes over tdc,but i will anyway,BE CAREFUL,Chris




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  4. #3
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    pm sent

  5. #4
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    The advice Chris has given you is the very best you will get from anyone. The reason you are seeing the difference between the port and starboard side is that you were rotating the flywheel in the same direction for both sides.

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    Even though test was done on each @ TDC?

  7. #6
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    Quote Originally Posted by bbezok View Post
    Even though test was done on each @ TDC?
    Yes, for sure. Do the port side clockwise and the starboard side counter-clockwise and you will see that your consistent differences go away.

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  9. #7
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    I'll try it that way first chance I have as well as the procedure Chris uses, just a bit leery on eating a ratchet handle......after all, they don't call them "on purposes".

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    Quote Originally Posted by bbezok View Post
    I'll try it that way first chance I have as well as the procedure Chris uses, just a bit leery on eating a ratchet handle......after all, they don't call them "on purposes".
    The test does not need to be done at 100 PSI...................a lesser PSI will produce accurate results as long as your "math" is correct and the likelihood of having to visit a dentist after the test is greatly reduced................LOL

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  12. #9
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    yes, I believe Chris said he does it @ 75lbs but I'm sure 50 will do.

  13. #10
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    I like to turn flywheel and pump it towards tdc like Chris said then you can see the whole picture 50 psi x 2

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  15. #11
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    Quote Originally Posted by eli View Post
    I like to turn flywheel and pump it towards tdc like Chris said then you can see the whole picture 50 psi x 2
    Yes sir.....................50 PSI and taking the loss in pressure x 2 gives a good reliable reading. So if the loss is 2 PSI, the leakdown % is 4%.

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  17. #12
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    Thanks guys, really appreciate the info.

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