Compression test numbers

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    Author Topic: Compression test numbers  (Read 921 times)

    Offline 67vertman

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    Compression test numbers
    « on: March 08, 2009 - 05:59:05 PM »
    I performed the compression test today.  Stock 1970, 318.
    I ran the test twice on each cylinder, dry both times except the # 5 cylinder, ran it dry then wet.
    Cylinder #
    8, 150 – 152 psi
    6, 140 – 144
    4, 135 – 145
    2, 148 – 140
    7, 140 – 145
    5, 80 – 80 Dry, 95 – 100 wet
    3, 145 – 142
    1, 138 – 140

    The motor has set for six years.  I think the number 5 cylinder is rings.

    How do the numbers look?
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    Ron - Born and raised in Southern California

    I got the 1970 Cuda, but still need the hot blonde to ride shotgun!

    First car -1969 Road Runner 383 4sp

    Current ride - 1970 Barracuda 440-6 4 sp Dana 60  (4:10)


    Offline Chryco Psycho

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    Re: Compression test numbers
    « Reply #1 on: March 08, 2009 - 08:32:30 PM »
    looks great except for # 5 , probably both rings & heads , the rings would bump the compression higher with oil generally
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    Challenger - You`ll wish You Hadn`t

    Offline 6packCuda

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    Re: Compression test numbers
    « Reply #2 on: March 08, 2009 - 09:07:19 PM »
    I would do a cylinder leakage test on #5. That will help to pinpoint the problem with that cylinder.
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    Dave

    Offline 67vertman

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    Re: Compression test numbers
    « Reply #3 on: March 08, 2009 - 10:57:51 PM »
    Quote from: 6packCuda on March 08, 2009 - 09:07:19 PM
    I would do a cylinder leakage test on #5. That will help to pinpoint the problem with that cylinder.

    I was thinking the same thing.  :2thumbs:

    All though it means I will have to buy a new tool.   :jumping:  Don't tell the wife though
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    Ron - Born and raised in Southern California

    I got the 1970 Cuda, but still need the hot blonde to ride shotgun!

    First car -1969 Road Runner 383 4sp

    Current ride - 1970 Barracuda 440-6 4 sp Dana 60  (4:10)

    Offline 71chally416

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    Re: Compression test numbers
    « Reply #4 on: March 08, 2009 - 11:38:54 PM »
    Sounds like a burnt exhaust valve to me. That's common with a high mileage SBM motor. Could also be a cylinder with some scoring or just the rings are siezed on that piston from sitting for 6 years. Might wanna try some penetrating oil in that one hole over night than run it for a few hours and see if the compression changes. The other cylinders are good for such an old motor.
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    Offline femtnmax

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    Re: Compression test numbers
    « Reply #5 on: March 09, 2009 - 12:15:45 AM »
     :iagree:
    The numbers didn't seem to come up enough for bad rings.  I could be wrong.
    If your on a budget, you could pull the head(s) and hand lap the valves (replace one?) so the compression comes up even on all holes, but not enough to overpressure the tired rings which would cause increased oil consumption.  With new valve stem seals could have it running for under $100.... But the plastic timing chain gear on the cam...or.... would be next.....
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    Phil

    Offline 72bluNblu

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    Re: Compression test numbers
    « Reply #6 on: March 09, 2009 - 03:19:44 AM »
     :iagree:

    #5 is a valve issue, not rings. In my experience most bad rings will come up to almost normal compression levels with some oil down the cylinder, unless the rings are completely shot. It may not even be a burnt valve, could just be carbon build up on the back of the valve. It might also just be a stuck valve if its been sitting that long, any valvetrain noise?
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    Offline 67vertman

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    Re: Compression test numbers
    « Reply #7 on: March 09, 2009 - 12:55:16 PM »
    Thanks for the input guys.

    I only let it warm up for about fifteen minutes before I did the compression test.  So, I am going to run it up to temperature a couple of times and retest it again and see what happens.  I am not planning on running this motor much right now anyhow.
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    Ron - Born and raised in Southern California

    I got the 1970 Cuda, but still need the hot blonde to ride shotgun!

    First car -1969 Road Runner 383 4sp

    Current ride - 1970 Barracuda 440-6 4 sp Dana 60  (4:10)
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