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Thread: Leak Down Test

  1. #1
    West Texas RXP skoepp's Avatar
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    Leak Down Test

    I borrowed a tester from a forum member.
    I have not every preformed one myself so wanted to be sure i get the proper procedure.
    Also searched and found nothing on how too.

    I realize that you have to get leak down on each cylinder with piston top and valves closed but wanted some pointers or tips so that i can get the correct readings the first time.

    Thanks

    Would like to do this today and if all looks good ride hard tomorrow.


  2. #2
    formerly Gold06RXP Turbo Nick's Avatar
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    Thread the tester into the spark plug hole. Connect tester to air source and zero out tester. Then connect tester to hose threaded intp spark plug hole. You will start to get a reading that will be some what high. Rotate engine counter clockwise using the 12mm allen in the pump untill u begin to feel strong resistance and you see the gauge drop in leak %.(the resistance is the air pushing back against the piston) Hold engine firmly in the position in which the lowest % is observed. That is your leak down %. You need to rotate the engine in order to close the valves in the test cylinder to get an accurate reading. If that seems to much you could always just remove the rocker shaft in order to ensure the valves are closed.

  3. #3
    DaveC's Avatar
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    +1, much easier and faster to just remove the rocker shaft. Costs you a set of shaft bolts, but you no doubt the valves are closed.

    Quote Originally Posted by GOLD06RXP View Post
    If that seems to much you could always just remove the rocker shaft in order to ensure the valves are closed.

  4. #4
    Water4fire's Avatar
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    Quote Originally Posted by DaveC View Post
    +1, much easier and faster to just remove the rocker shaft. Costs you a set of shaft bolts, but you no doubt the valves are closed.
    I agree remove your rocker shaft. If rocker bolts were new reuse them.

  5. #5
    Moderator beerdart's Avatar
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    TDC is your friend,

  6. #6
    dnielsen's Avatar
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    Quote Originally Posted by beerdart View Post
    TDC is your friend,
    +1, TDC on each cylinder tested is the only way to get an accurate % reading. A good dial indicater setup inserted in through the spark plug hole will allow you to get each piston "centered" at TDC. Pull the air intake off the charger and rotate the engine with the nut on the charger impeller.

  7. #7
    West Texas RXP skoepp's Avatar
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    Thanks for the replys.
    is it really that inaccurate with bolts in?
    Or I guess I should ask if it is that hard to get good readings with out removing rocker shaft bolts.

    I did not get to it today (R and R) and taking the ski out tomorrow.
    Can't resist. First day in 90 days in the 80 degree mark.
    I hope I am under proped with the 20 difference in degrees.
    Mo power.
    Might be getting close to swap to the winter prop.

    Probably leak test it Monday and I am sure will have a question.

  8. #8
    Here's the problem that nobody mentioned. When you apply air with the valves closed, & piston anywhere between TDC and BDC, it creates lots of rotational force. If you get it at exactly TDC, then the force is minimized, not as hard to hold the crank in place. The most force generated is exactly half way between TDC and BDC, FYI. Better hold it good or you will have an unpleasant surprise. Note that at TDC it will either try to go CW or CCW, depending on what point you are away from true TDC.

    No reason to remove rocker shaft bolts....

  9. #9
    Hondapro210's Avatar
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    Looks like you received the leak down tester, and yes we finally got some cooler weather...

  10. #10
    Hondapro210's Avatar
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    Quote Originally Posted by Sea Dood View Post
    Here's the problem that nobody mentioned. When you apply air with the valves closed, & piston anywhere between TDC and BDC, it creates lots of rotational force. If you get it at exactly TDC, then the force is minimized, not as hard to hold the crank in place. The most force generated is exactly half way between TDC and BDC, FYI. Better hold it good or you will have an unpleasant surprise. Note that at TDC it will either try to go CW or CCW, depending on what point you are away from true TDC.

    No reason to remove rocker shaft bolts....
    +1 Yes I have seen guys doing leak down test on vehicles and once air is applied and your not exactly at TDC your gonna have a 1/2 rachet slapping back at you.

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