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post #1 of 9 (permalink) Old 09-21-2005, 08:12 PM Thread Starter
 
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cehcking compression out of car

I was checking an engine that is out of the car using a ratchet to turn the engine over. All the plugs are removed and nothing is hooked up to engine . I was wondering if the compression should be the same as if it was in the car turning over by the starter.

there is no way I am able to turn the engine over as fast as the starter can but it seems that I should get similiar compression readings. Is this true or should there be some difference?

The reason I am asking is cause I was looking at an engine that supposedly had 67k on it. The compression (turning over cylinder about 3 times) was about 30pds for all cylinders except one. One should up as zero. I rechecked it several times but still nothing. Not even a twitch. I am not getting engine but was wondering if the engine was in the car using the starter to turn it over would the compression be the same?

As I understand it the 3.8 should have at least 100 psi per cylinder. Is this the same with the engine out of the car doing it the way i did?
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post #2 of 9 (permalink) Old 09-21-2005, 08:58 PM
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Without a starter turning the motor over, the compression numbers are going to be way down. I would reccomend that you bolt up your trans and starter to the motor and use a battery to turn the starter and check compression that way.

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post #3 of 9 (permalink) Old 09-21-2005, 09:00 PM
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well, keep in mind that when you check the compression on an engine while it's in the car still and hooked up, the engine probably turns 20-30 times before you let off.

So, Get crankin!

RIP Joel Bender and Preston Smith. The world will never be the same without you.
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post #4 of 9 (permalink) Old 09-21-2005, 09:27 PM Thread Starter
 
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should I be concerned about that dead cylinder though? I figured it would be off, but it came up as zero while the others showed 30.
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post #5 of 9 (permalink) Old 09-21-2005, 09:29 PM
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yes, I would be... could be a bent valve, cracked head, blown gasket, burned piston, broken piston, bad rings, etc...

RIP Joel Bender and Preston Smith. The world will never be the same without you.
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post #6 of 9 (permalink) Old 09-22-2005, 06:51 AM
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Do a leak down test!

You don't have to turn the engine over for that, and it is a 100 times better test than a compression test.

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post #7 of 9 (permalink) Old 09-23-2005, 10:06 PM Thread Starter
 
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what do I need for a leak down test? All i have is a compresison gauge right now.


I ended up taking the time to bolt my tranny up and use the starter. I got good compression on one side about 150 across on all three cylinders after three revolutions. THe other side sucked. Got 120, 30, 121. Looks like another head gasket or something else. Time to return the engine and start looking for another.
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post #8 of 9 (permalink) Old 09-23-2005, 10:10 PM
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man, I would just go buy a newer style 3.8... get a 96-98 engine for a bolt in...

RIP Joel Bender and Preston Smith. The world will never be the same without you.
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post #9 of 9 (permalink) Old 09-27-2005, 09:23 PM Thread Starter
 
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A 96-98 will work in my car? I thought only 89-95 was a good mate up for my car. I'm not looking for a direct bolt in. I can use my intakes TB and accesories if I had too. Really all I need is a good block, internals, and heads.
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