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Compression test out of car

Old 08-17-15, 03:48 PM
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Compression test out of car

I have a long block (and lots of aftermarket goodies) I bought about 3 months ago, just getting around to tearing it down and doing a compression test on it. It came out of a running car, no smoke, no waterloss etc.

No real history on the motor though.

Reading the compression test instructions from here: Rotary Tech Tips: How to compression check a rotary engine as its been a while since I have done a compression test.

No UIM on the block, just hooked the starter up to a strong battery (even tried a running car with jumper cables), leading plugs out, compression tester (holding the valve open) and I am seeing 73ish psi very consistently and even pulses. I know this is not good, but I also read most of the tests saying you needed to warm up the car first or it would be inaccurate. I can't do that with this block sitting out of the car.

Lastly I need to swap the starter and make sure its not weak as well but it sounded alright...

Anyone else have some info on accuracy of not having the engine warmed up or doing a out-of-car compression test like this ? the document says it would be higher then accurate on a cold engine, so maybe I have answered my own question...

Thanks!
-Brian

Last edited by elfking; 08-17-15 at 03:52 PM.
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Old 08-17-15, 03:54 PM
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Compression reading would only be lower with the engine warmed up. Could me a multitude of reasons why the readings are that low. If all faces seemed even I would say install it and run it.
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Old 08-17-15, 04:51 PM
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Originally Posted by djseven View Post
Compression reading would only be lower with the engine warmed up. Could me a multitude of reasons why the readings are that low. If all faces seemed even I would say install it and run it.
I agree, there could be plenty of reasons to being inaccurate at this point.. I'll install it and see how it does.. I came across it and the other goods for such a good deal I couldn't pass up..

The pulses are very even , ive for sure compression tested with failed apex / corner seals and know what it sounds / feels /looks like on the gauges.. so this looks good to me.
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Old 08-19-15, 09:48 PM
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Do you have access to a fd in your area or a Buddy's? Why not use the exact tester and method on their cold motor and see what you get.

Then compare numbers.
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