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Old 11-05-2002, 09:49 AM
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Thumbs down "Compression Drop" on New Engine Rebuild

Hello,

My compression was slowly going up on my engine rebuild but I have been driving it a little hard and the compression is going back down again.

If I drive it easy for the next 500 miles could the compression start coming back up again? Will the rings ever seat now?

I have 200 miles on a fresh 289 engine rebuild.

Thanks, Greg.

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Old 11-05-2002, 10:47 AM
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just one cyl. or all 8? you shoulda been takin it easy till after 500. how many 6500 rpm shifts?
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Old 11-05-2002, 10:58 AM
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It's about 50/50 4 of the cylinders are at about 150-155 and the other 4 are between 136-140.

I gave the low ones a shot of oil they came up to 160. I don't know if that means that all of them will eventually come up to 160 or if that's just the maximum compression capability of each cylinder.

When I fist got the car home they were all about 130, then a month later they were all about 150-155 and then more recently (after driving it at full accelleration a few times) some of them are down to 136-140.

But....I don't know if this is perminent or temporary.

Greg.
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Old 11-05-2002, 12:24 PM
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More like highly dependant on conditions and atmospheric pressure. Compression is only valid when doing a comparison between cylinders. Actual readings are highly variable and depend on too many factors to be compared from day to day. Simple things like humidity affect readings greatly.

Don't worry about it.
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Old 11-05-2002, 02:21 PM
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I agree don't worry about it. A leak down is the only accurate way to tell ring seal. Any cyl will come up on pressure when oiled (oil doesn't compress)because it lowers the cylinder volume. Modern rings seat almost immediately if they had a good hone to work off of. You could also run through the lifter adj. again maybe some have pumped up and are holding the valves open a little longer, don't automatically assume it's a ring problem. If you are sure all was done correctly run it a while longer and then check it.
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Old 11-05-2002, 03:44 PM
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Be sure you valve adjustment is good and drive it reasonably and check it after 2000 miles. It will settle in. Worry if you see a cylinder with 60 pounds at that point. For now, the problems are probably more in your head (between your ears) rather than in your motor.
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