454 Stock Compession Test Results...??
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454 Stock Compession Test Results...??

  1. #1
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    Default 454 Stock Compession Test Results...??

    Hey Guys,

    I dont really know whats its supposed to but I had an urge to do a compression check on the boat last week and here are the results.. Cranked each one about 8x to reach the readings

    1-120 Psi
    2-110
    3-105
    4-100
    5-100
    6-100
    7-120
    8-100

    I didnt realize that Im supposed to test the rings using regular motor oil when doing a compression, I used WD40 instead, Cyl 4 jumped to 110 and 3 went to 110 also, none of the other changed when using WD40. I will have to re-check with an oil squirter.

    Its a '90 stock 454bbc by Hardin Marine 4-bolt. Its never been rebuilt to the best of my knowledge.

    All of the plugs were black around the bottom ring, but the ceramic was white, ground electrode were clean, and some of ground electrodes were even a coffee/mocha color, but not all of them, the others were just clean. They are brand new plugs MR-43T's.

    Based upon the compression, does this thing need a rebuild?

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    Senior Member sleekcraft137's Avatar
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    Quote Originally Posted by headshothills View Post
    Hey Guys,

    I dont really know whats its supposed to but I had an urge to do a compression check on the boat last week and here are the results.. Cranked each one about 8x to reach the readings

    1-120 Psi
    2-110
    3-105
    4-100
    5-100
    6-100
    7-120
    8-100

    I didnt realize that Im supposed to test the rings using regular motor oil when doing a compression, I used WD40 instead, Cyl 4 jumped to 110 and 3 went to 110 also, none of the other changed when using WD40. I will have to re-check with an oil squirter.

    Its a '90 stock 454bbc by Hardin Marine 4-bolt. Its never been rebuilt to the best of my knowledge.

    All of the plugs were black around the bottom ring, but the ceramic was white, ground electrode were clean, and some of ground electrodes were even a coffee/mocha color, but not all of them, the others were just clean. They are brand new plugs MR-43T's.

    Based upon the compression, does this thing need a rebuild?
    was the motor warm when you did the test?? to me that sounds low but it could also be your test gauge you are using. I just did my mostly stock 455 and i was in the 170 range across all cyl.
    Last edited by sleekcraft137; 05-24-2010 at 03:10 PM.

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    tintingsandiego krusn56's Avatar
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    I have a mild 460 with 135-140 all around
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    Quote Originally Posted by sleekcraft137 View Post
    was the motor warm when you did the test?? to me that sounds low but it could also be your test gauge you are using. I just did my mostly stock 455 and i was in the 170 range across all cyl.
    HAHA...Unless you consider 100 degree weather siting in the driveway warm...No I didnt. I picked up a new tester at Autozone that screws in.

    I didnt notice any of the cylinders dropping or loosing pressure, and if I did, It was the tester so I would reseat the tester and it then it didnt leak.

    I know theres a bunch of variables that can be added to the mix, like piston type, head type, etc...I just figured I could get a number for a stock 454bbc to give me a relative point on whether or not is time to rebuild.

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    Senior Member sleekcraft137's Avatar
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    Quote Originally Posted by headshothills View Post
    HAHA...Unless you consider 100 degree weather siting in the driveway warm...No I didnt. I picked up a new tester at Autozone that screws in.

    I didnt notice any of the cylinders dropping or loosing pressure, and if I did, It was the tester so I would reseat the tester and it then it didnt leak.

    I know theres a bunch of variables that can be added to the mix, like piston type, head type, etc...I just figured I could get a number for a stock 454bbc to give me a relative point on whether or not is time to rebuild.
    hook the boat up to the hose, let it run and warm up. That will let the heat expansion seat the rings and valves properly and oil your cyl up. A screw in type is a MUST!! I bet you were losing between 20-40 lbs by using the push on type. The main thing is to have all the cyl within 15 lbs or so. Let us know how it comes out!......also make sure its at WOT when you test!!!
    Last edited by sleekcraft137; 05-24-2010 at 04:37 PM.

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    Quote Originally Posted by sleekcraft137 View Post
    hook the boat up to the hose, let it run and warm up. That will let the heat expansion seat the rings and valves properly and oil your cyl up. A screw in type is a MUST!! I bet you were losing between 20-40 lbs by using the push on type. The main thing is to have all the cyl within 15 lbs or so. Let us know how it comes out!......also make sure its at WOT when you test!!!
    Thanks Sleek, it was a screw in, it was NOT a a push in, but i totally forgot about holding the throttle wide open. I will test again...

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    Senior Member slotracer's Avatar
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    [QUOTE=sleekcraft137;1105638]hook the boat up to the hose, let it run and warm up. That will let the heat expansion seat the rings and valves properly and oil your cyl up. A screw in type is a MUST!! I bet you were losing between 20-40 lbs by using the push on type. The main thing is to have all the cyl within 15 lbs or so. Let us know how it comes out!......also make sure its at WOT when you test!!![/QUOTE]
    why does it have to be at wot?
    slot
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    Senior Member crzyjay74's Avatar
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    WOT I have never heard of that, your only supposed to turn the motor over a few turns without starting to get the correct rating from Ive been told.Plus you wont get any leak down on the guage anyway, since most of the guages have a one way valve stem.in order to get the correct PSI rating and leak down you need to remove the valve inside the guage and unadjust the valves fully,then turn the motor over 4 to 5 revolutions. This is the way I have been told to do it, my .02

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    Senior Member 2002CP19's Avatar
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    [QUOTE=slotracer;1106272]
    Quote Originally Posted by sleekcraft137 View Post
    hook the boat up to the hose, let it run and warm up. That will let the heat expansion seat the rings and valves properly and oil your cyl up. A screw in type is a MUST!! I bet you were losing between 20-40 lbs by using the push on type. The main thing is to have all the cyl within 15 lbs or so. Let us know how it comes out!......also make sure its at WOT when you test!!![/QUOTE]
    why does it have to be at wot?
    Its so air can get in the cylinder.
    Quote Originally Posted by schick View Post
    Hold it firmly on the ground, a few pelvic thrusts should do the trick. If not repeat till satisfied!

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    Senior Member crzyjay74's Avatar
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    Air will get to the cylinders without WOT, but I understand what your sayin, But you do NOT want to start the engine for the compression test.

  13. #11
    Senior Member sleekcraft137's Avatar
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    Quote Originally Posted by crzyjay74 View Post
    Air will get to the cylinders without WOT, but I understand what your sayin, But you do NOT want to start the engine for the compression test.
    no, you want to disconnect the coil. Crank the motor with the carb at wot.

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