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Thread: 4AGE smallport low compression help!

  1. #1
    Senior Member shortround's Avatar
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    Default 4AGE smallport low compression help!


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    Hey guys,

    I recently installed a smallport 4AGE to use temporarily whist waiting for an engine rebuild.

    It was sold as a "running engine", with the ad saying 150psi across all cylinders - sounded a little low, but I was only planning on using it till the end of the year.

    However after I installed the motor, I found that this was not the case. It feels and sounds like its running on 3 cylinders, and is blowing white smoke.

    Here are the results of the dry compression test after warming the engine to operating temp:

    1 - 190
    2 - 60 and did not hold pressure
    3 - 60 and did not hold pressure
    4 - 210

    It's weird that the gauge looses pressure on cyls 2 and 3 after maxing out at 60psi when cranking. I don't think it's something I am doing wrong, as I immediately swapped the gauge back to cyls 1 and 4, which held pressure until I pressed the release valve, as did the results on cyls 2 and 3 below VVVV

    I then did a wet compression test on cyls 2 and 3, with about 1/2 tablespoon of oil:

    2 - 205
    3 - 220

    There is also a reasonable amount of pressure coming out of the dipstick hole, but there is NO oil in my catch can, so it sounds like its probably rings?

    It was suggested that I do a leakdown test, however I don't have an air compressor etc.

    Where would the issue likely be?? Bottom end or head gasket/top end? The later I can fix with spares I have lying around.

    Cheers,
    Andrew.

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    Senior Member ach_66's Avatar
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    White smoke and low compression between 2 and 3 sounds like head gasket to me?

    Burning oil would be blue smoke and smelly.

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    Veteran lolwat's Avatar
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    if you oil them, noramlly help the rings seal, put a vacume guage on it see how still the needle is (can show sign of valve issues) my 4a has a ring (pos piston) it fills a medium milo can with oil in like 5 mins, and covers engine bay in oil(rear muffler is dripping with oil)
    Last edited by lolwat; 16th September 2012 at 11:14 PM.

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    Veteran maxhag's Avatar
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    As "Azz" has said above, sounds like a HG blow between two cyls. Has actually happened to me before, with simular symptoms....

    Ie; This -

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    Veteran timbo's Avatar
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    Those compression numbers on 1 and 4 are relatively low. When I did a compression test on my smallport it was 225 on all four. As everyone said it seems to be a blown HG, take the head off and have a look, worse case is you need to pull the motor out anyway.

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    Noooob
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    I'd put money on the head gasket being gone as well

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    Senior Member shortround's Avatar
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    Thanks for the replies lads. I'm hoping it's the head gasket or even the head as I have spares of both lying around. I'll start pulling the head off tonight.

    timbo - my compression gauge is just an el-cheapo of ebay, so I am not too worried about the exact numbers. The engine I recently pulled out of the car had around 200-215 across all cyls and it still pulled strong!

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    Ah righto, they are never foolproof but give you an idea. Good luck with it, HG is easy, rings will be easy because you've already taken the head off!

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    Veteran lolwat's Avatar
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    if you think its between cyclinders, put a plug in 2 and test 3 see if ti changes at all

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    Senior Member shortround's Avatar
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    Quote Originally Posted by lolwat View Post
    if you think its between cyclinders, put a plug in 2 and test 3 see if ti changes at all
    Thanks Michael, I'll give it a go.

    Need to recharge the battery first

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