Has anyone completed a compression test on a healthy Mercury 500HP (Carb) engine? If so what is the average. Thanks in advance!
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03-02-2010 07:19 PM
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03-02-2010 08:28 PM
I think you want consistancy. Doing it on a warm engine is more accurate. For example, if you have 145-155 on all cylinders and 1 or 2 are only at 110, you have something going on. Oh, and dont forget to keep the throttle open while doing it.
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03-02-2010 08:53 PM
I just do not know if the engines in question were rebuilt to stock or if the compression ratio was bumped up....the cranking compression should explain this.
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03-03-2010 04:09 PM
Hard to tell without opening up an engine. A cam with longer than stock duration will cause the engine to have lower cranking compression while higher comp. pistons will cause it to have higher. Add these two together and you might have the same cranking compression as stock. Can't you ask the original owner or mechanic?
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03-03-2010 04:23 PMCompression tests tell little. Do a leakdown.
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03-03-2010 05:02 PMTo re-phrase the question. Should a healthy broken in but not worn out HP 500 carb have a cranking compression of 150 average or 180 average? No reason to do a leakdown as the compression is consistent across the board and a leakdown does nothing to predict dynamic compression. The motor was rebuilt and getting info from the builder may be difficult since it has been a few years since the re-fresh and the original owner is not known. Just trying to use this as a tool to decide if it was rebuilt to OEM spec. The lake test among other things will also be done, but for now this is what we have available. I realize its possible for the compression / cam to be altered from OEM and still net the same cranking compression. Just trying to get a baseline to compare against.
Thanks,
Craig
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03-03-2010 05:35 PM
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03-04-2010 08:26 AMI checked mine with the throttle wfo and it was between 142 and 147 on all cyls. And it had some hours on it.
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03-06-2010 12:42 PM
Stock they are around 150.
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