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Thread: Low compression SR20 diagnosis

  1. #1
    Guest Jonnay's Avatar
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    Low compression SR20 diagnosis

    Hi people,

    My friend has been offered a chance to buy an SR20 which is down on compression. We tested it and it was 4.5 bar, 8.5 bar, 4 bar, 8.5 bar. So low on all, but especially low on 1 and 3.

    Before he goes ahead and does it, is there any easy way to tell what the culprit is likely to be without taking off the head? I think probably ringlands but seems odd that all 4 are suffering the same problem. It's currently in the car and can be spun over (won't start).

    Any help would be gratefully received!

    Cheers, Jon

  2. #2
    Guest kriskouki's Avatar
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    I would run another compression test again. ....Do a wet test too if you can.....

    Low compression test can be caused from many things like head gaskets failure, wrapped head cylinder, valve leaks, or even bad piston rings.....

    I would suggest to confirm the results again, and if you still have the exact same results. ...i would suggest check other type of things such as blow-by.....Just to see how much oil coming out of the blow-by hoses.....And, if there is bunch of oil from blow-by, i would suggest to overhaul that engine

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  3. #3
    Guest Jonnay's Avatar
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    Thanks for the advice. the lad who owns it swears blind that it was running fine until last month when the turbo went. Had that reconditioned. Put it back on and now low compression.

    My friend's getting it cheap enough, would just be nice to have an idea of what work is gonna be involved before it's out the car and can't be spun over quite as easily.

  4. #4
    Guest kriskouki's Avatar
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    Compression test can be done with the engine is out of the car too....i have done numerous of them while the engines were sitting on the ground.........

    Low compression isn't something related to the turbo.....so i don't think that bad or good turbo can be involved with this


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  5. #5
    Engine Builder Mark's Avatar
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    Firstly they are not all low, 8.5 bar isnt bad for a used engine as its around 120-125psi.

    Do the test again dry (making sure the throttle is open) then again wet. If the 2 low numbers jump up then its the rings/bores, if they stay around the same its the head or gasket.
    Quote Originally Posted by silverzx View Post
    I like Mark, he seems fair.
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    Mark is right.

  6. #6
    Guest Jonnay's Avatar
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    Quote Originally Posted by Mark View Post
    Firstly they are not all low, 8.5 bar isnt bad for a used engine as its around 120-125psi.

    Do the test again dry (making sure the throttle is open) then again wet. If the 2 low numbers jump up then its the rings/bores, if they stay around the same its the head or gasket.

    Thank you very much for the advice. I was told 10 bar was about right/maybe on the low side for a used engine so I was obviously misinformed.

    Will do the checks you suggested tonight

  7. #7
    Guest ANDY black s13's Avatar
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    The engine needs pulling apart as it has a fault somewhere,so ask seller if you can pull the head off it before you buy it ?
    SR's can crack exhaust valves and cause a slight comp loss or a chunk of valve drops off = big comp loss,stock pistons also can crack ring lands
    the dead turbo bit makes me think it has seen a lot of boost so suspect detonation/getting super hot and the valves/pistons will suffer the above
    possible a lot of det and piston crowns have distorted causing blow by and the comp loss

  8. #8
    Banned sideways14a's Avatar
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    As above, humped turbo could be because of hefty boost - heafty boost on iffy fueling = burnt valves... yup i went there.

  9. #9
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    A cylinder leakage test can help you find the compression loss, a very good test.

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