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Checking compression on non-running engine

Discussion in '1982-Present GM Diesel' started by jolane, Oct 22, 2005.

  1. jolane

    jolane 1/2 ton status

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    I have another newbie question on the 6.2L I was working on today. If I cannot get it running without major work and expense right now, I would at least like to check the compression before I pull the engine. Is this possible?
    The engine would be cold. How do I check the compression (through the glow plug hole or the injector)? Do I need to use oil inside the cylinder? Is a fresh set of batteries good enough for cranking speed? What size of adapter do I need to correctly hook it up the engine?

    Thanks Again,
    Joshua
     
  2. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Never use oil in the cylinders to do a compression check on a diesel. They're compression ignition and burn a variant of oil...

    You'll need a special compression tester, 6.2's should register well over 300 psi and every tester I've seen doesn't go that high.

    Rene
     
  3. jolane

    jolane 1/2 ton status

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    tRustyK5,
    Thanks for the reply. I have read a lot of your posts during my research.

    Do you have any idea where I would find a compression tester for this engine?
    Thanks,
    Joshua
     
  4. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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  5. diesel4me

    diesel4me 1 ton status Premium Member

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    Tester..

    They sell them,they are just more expensive than your typical gas engine compression tester..I think Sears might sell them,amd I know Lysle or K-D Tools,and Snap-On sell them..you might need an adapter for the 10mm thread in the glow plug holes that might not come with it,and is sold separately sometimes..all told they cost about 100 bucks for a decent one..

    My brother cheated when he wanted to test compression of his 6.5--he bought just the adapter dewhickey,and used an air PSI gauge off an old compressor that went up to 500 psi he had lying around--but you had to watch it while cranking,to get a reading,as it didn't have a check valve like the store bought one would to "hold" the reading..nor did it have a "release" button..
    I've been tempted to make my own using a similar gauge,and the check/release valve off the cheap gas engine compression tester I have, that has a smashed glass that went over the gauge. :doah: .maybe I can just swap the broken gauge on that one for the one that goes up to 500 psi..I have 2 gauges already.. :thinking:
     
  6. jolane

    jolane 1/2 ton status

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    Wow, I guess they are more common than I thought. I searched online at Checker and Autozone. Never thought about Harbor Freight. I hate buying stuff from HF (except certain low use specialty tools like portapower, etc). their kit looks very complete though, and the only thing that might need to be changed is the gauge, which shouldn't be expensive. Thanks tRustyK5 for the search!

    As for checking the compression, does the engine have to be warmed up to at the ~300psi mark? What should I see on a cold engine, if I can't get it started? I figure that if the compression test works out, I will be inclined to have the injectors and IP rebuilt, if I cannot get it running per the other thread and your suggestions. If the compression is abnormally low though, I will have to do a major reconsideration before dropping the money on the IP.
    Thanks again very much!
    Joshua
     
  7. imiceman44

    imiceman44 1 ton status

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    The kit from HF is actually a good one, although not cheap.
    I have it and it had the adapter for the 6.2l
     
  8. Steve_87K5

    Steve_87K5 1/2 ton status

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    If you have access to a lathe, make an adaptor out of an old glow plug.

    When I tested my 6.2, I had all the other glow plugs out. Don't know
    if this was the correct procedure or not. Anyone know ?
     
  9. jolane

    jolane 1/2 ton status

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    Steve_87K5,
    That is a great idea! I could simply bore out the glowplug, leaving only the threads and sealing surface, and make my own. I bet I could even replace my current gasser copression tester gauge with a high pressure one, and have the complete setup with release button.
    Thanks!
    Joshua

    As for testing the compression, what is the correct procedure. As Steve said, should all the glow plugs be out to help the engine turn faster?

    I will learn about this one day, thanks for contributing to my future knowledge!
     
  10. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    I don't see any reason to have the GP's installed. When I compression check a gas engine I remove all the spark plugs... :dunno: :thinking:


    Rene
     
  11. imiceman44

    imiceman44 1 ton status

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    Yes you are supposed to have all glow lugs out.
     
  12. jolane

    jolane 1/2 ton status

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    Thank you! I will take them all out.
    Joshua
     

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