compression leakdown test help?
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compression leakdown test help?

  1. #1
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    Default compression leakdown test help?

    trying to perform leakdown test on my hp500. tried to put at TDC but when i start to fill cylinder it pushes piston back down, try to hold crank but after 70 lbs or so cant hold it. everything i read says test at TDC except instructions with guage from summit says bottom dead center. tried that also but cant seem to get both valves closed either leaks through exhuast or intake. it has billet pulleys on it so no crank bolt without removing safety wire and pulley so im turnig with prop shaft. , i've looked on line and it looks simple. what am i missing????

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  3. #2
    gn7
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    Well, right off, you know you pulley is wrong. Because if your piston was really at TDC, you could put 500 psi in the cylinder and it wouldn't go to the bottom.
    Any time the piston is at the bottom of the bore, there will be a valve open.

    If you want to test at the bottom, you'll need to pull the rockers off.



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    Quote Originally Posted by gn7 View Post
    Well, right off, you know you pulley is wrong. Because if your piston was really at TDC, you could put 500 psi in the cylinder and it wouldn't go to the bottom.
    Any time the piston is at the bottom of the bore, there will be a valve open.

    If you want to test at the bottom, you'll need to pull the rockers off.
    i assumed that at the bottom. but even at tdc with pressure what is stopping the piston from pushing the crank??? (all plugs are removed) i've tried numurous times holding prop, and doesnt seem to leak until i cant hold prop anymore. i read that 100psi is appx 900lbs of pressure on the piston??? thanks

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    Senior Member stix818's Avatar
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    x 2 with what GN said.. Sounds like your TDC mark is off. Try stopping a couple degrees before and after.. I prefer to test at TDC because that's where combustion is happening..
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    No reason to test at bottom. Summit is ****ed.
    Get close to TDC, stick a long skinny screwdriver in the plug hole. Rock the crank back and forth. You SHOULD be able to get very close to TDC if not right on by watching movement.
    Wags

    Oh, and yes, at TDC the crank won't turn. You are pushing directly straight down on the crank. It has no desire to turn. Once you get a few degrees off of TDC, the piston will force the crank down. (rotate crank)

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    Quote Originally Posted by wagspe208 View Post
    No reason to test at bottom. Summit is ****ed.
    Get close to TDC, stick a long skinny screwdriver in the plug hole. Rock the crank back and forth. You SHOULD be able to get very close to TDC if not right on by watching movement.
    Wags

    Oh, and yes, at TDC the crank won't turn. You are pushing directly straight down on the crank. It has no desire to turn. Once you get a few degrees off of TDC, the piston will force the crank down. (rotate crank)
    thanks to all. this is what i am trying, but must be missing a little

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    Put your other plugs in. You have to be spot on with them all out.

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    Sounds like your first order of business might be locating the actual TDC rather than what the damper/pointer now says. Once determined move your pointer if you have one - if not, clearly and permanently mark your pulley to identify actual TDC. There is a piston stop tool that works well to determine it. From there follow what Wags says.
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