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Technical 95% leakdown

Discussion in 'The Hokey Ass Message Board' started by Nich, Sep 12, 2019.

  1. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 1,657

    2OLD2FAST
    Member
    from illinois

    Having to Wade through a bunch of " You've got your muffler clamp to tight " gets tiresome , some times I just try to state the obvious and move on , Sorry to have offended you .....
     
  2. Got a 100 psi in my head right now! Put the valve cover back on! Tape over all breathers. Tape the carb flange..Tape the exhaust port ..Plug in the air..Report back..Geez
    The piston won't move if it's at exact TDC.
     
  3. lippy
    Joined: Sep 27, 2006
    Posts: 3,988

    lippy
    Member
    from Ks

    Mark he'll have a black eye from the breaker bar if it ain't at TDC and the piston and rings are fine, and valves. LOL
     
  4. lippy
    Joined: Sep 27, 2006
    Posts: 3,988

    lippy
    Member
    from Ks

    Sorry, feeling spunky tonight. Lol. Lippy
     
  5. RichFox
    Joined: Dec 3, 2006
    Posts: 9,727

    RichFox
    ALLIANCE MEMBER

    You mean like someone telling him to back off the valve adjustment when he said he removed the rockers? I know what ypu mean. I dislike answers that don't make any sense myself.
     
    ottoman likes this.
  6. lippy
    Joined: Sep 27, 2006
    Posts: 3,988

    lippy
    Member
    from Ks

    Rich, does taking the rockers off mean the valves should be closed ? What if I'm on overlap? What if my degree wheel is off? What if I'm a smart ass? What if it's a two stroke!o_O I agree , I see a big hole in this theory. A 96 percent hole.;)
     
  7. lippy
    Joined: Sep 27, 2006
    Posts: 3,988

    lippy
    Member
    from Ks

    Gunsmoke is on!! Later:D
     
  8. Ebbsspeed
    Joined: Nov 11, 2005
    Posts: 4,668

    Ebbsspeed
    ALLIANCE MEMBER

    I've never heard this before but I guess it could happen. My question would be, if it's not good to decelerate from a high speed run on an old worn out motor, what are my options? An endless high speed run?

    Eventually I'll run out of road or fuel.......

    Like @Mark Yac said, if the piston is at exact TDC the piston won't move. With 96% leakdown it probably wouldn't move no matter where the crank was.
     
    Desoto291Hemi likes this.
  9. LOL! :D We used to say, "Put a brick on it!"
     
  10. gimpyshotrods
    Joined: May 20, 2009
    Posts: 16,144

    gimpyshotrods
    Member

    Pull the head. This should be visible.

    Yeah, hearing where all this air is going would be good; however, if you really are moving that volume of air, it's gonna have to come apart, anyways.

    Also, always listen to Rich Fox. He knows this stuff inside and out, and won't shine you on.
     
    David Gersic likes this.
  11. gene-koning
    Joined: Oct 28, 2016
    Posts: 1,319

    gene-koning
    Member

    As to a possible cause, My sister's 1st husband had an off topic car with a SBC. He had a lot of trouble with cylinder #8, had it apart 3 or 4 times. Finally he discovered that the valve covers he had did not have a baffle on the inside of the cover below the pcv valve. Long story short, the pcv was sucking the oil off the #8 rocker assemblies at some rpm above 2,000. The short term dry valves caused all kinds of problems that didn't show up until after the damage was done. After he added the baffle under the pcv valve, he quit having issues with #8.
    I think I have seen more then my share of the really strange stuff that can happen in the automotive world, so all I can do is tell people what I've seen, its their choice to investigate the possibility they may or may not have the same issue. Gene
     
    David Gersic likes this.
  12. boring-hop-yard
    Joined: Feb 24, 2008
    Posts: 74

    boring-hop-yard
    Member

    For those of you that may have not performed a leak down test.
    You want the piston at TDC to assure the intake and exhaust valves are closed.
    If the piston is not at TDC the crank will rotate when you start slowly applying air into the cylinder.
    The tester has a air pressure adjustment that allows you to back it all the way off to 0 or dial in 100 percent of the air being put into the tester.
    Mac Yac, I have tested engine on the bench that had all the openings taped off and you will get a nice "pop" when it blows out the opening that is leaking
    I still have a hard time understanding the amount of cubic feet of air going through the engine without being able to detect it. It should sound like a 96 psi jet engine going off inside the engine.
    The only time I have seen that amount of loss was from a 1/4 inch hole in the top of the piston from detonation.
    You could also try the test again but use a section of hose to listen for the air escaping.
    Do you have a scope to look down the spark plug hole?
     

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