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#1
07-29-2007, 04:11 PM
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Compression test results Help
Guys, whene doing a compression test on a bone stock 75 Pontiac 400 (S Code)what should i be looking for, PSI Wise . I did the test on a cold engine and these are the results:
1)35, 3)45, 5)40, 7)40, 2)40, 4)45, 6)40, 8)40. Keep in mind this was a cold motor not run for a few days. I understand these are low comp. motors and i guess i am looking for consistancy. This motor has 80K miles on it. THANKS John |
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#2
07-29-2007, 04:41 PM
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Well if it's PSI you are either missing a one in front of those numbers or you have no piston rings installed. Are you sure you did it correct? Need to open the throttle all the way (with the coil disconnected) and let it crank at least 5 times until the gage no longer goes higher.
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"The Mustang's front end is problematic... get yourself a Firebird." - Red Forman |
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#3
07-29-2007, 05:02 PM
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Did a timing chain jump?
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#4
07-29-2007, 05:09 PM
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Get the engine up to operating temperature and try again.
Make sure the throttle and choke blades are both wide open. Remove all the spark plugs so it will crank fast enough to give you some valid results.
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1964 Tempest Coupe LS3/4L70E/3.42 1964 Le Mans Convertible 421 HO/TH350/3.08 2002 WS6 Convertible LS1/4L60E/3.23 1966 VW Type 2 Single Cab Pickup 140hp 2276 1956 VW Type 2 Panel Van 36hp 1200 1957 VW Type 1 Beetle 180hp 2276 |
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#5
07-29-2007, 05:33 PM
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Quote:
That or the valves are'nt adjusted right or are'nt sealing very effectively. Do a leakdown test,or at the very least take the valve out of the compression tester rig and pump some air into a cylinder and listen to where it's leaking from. Even cold the numbers should be way higher. HTH. |
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#6
07-29-2007, 07:07 PM
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O.K i think i found my problem. It may be my Comp. tester. I took out the shrader valve and did the test(of course it will not hold the psi in the guage) However it went up to 140 psi. Also keep in mind this is a good running motor. I am just assesing it's condition since the car is new to me.
Even though the guage is not holding the psi the fact i am getting the 140 psi is a good thing. What do you guys think? John |
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#7
07-29-2007, 07:50 PM
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With one cylinder at 135 and one at 145, 140 psi is good for a motor with 80K.
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Its ok to giggle and snicker, Dont laugh and point Last edited by Ollie; 07-29-2007 at 07:57 PM. |
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#8
07-29-2007, 07:58 PM
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Yeah,140 would be about what I'd expect for a low comp 400 that has some miles under it's belt.
I would replace the schrader valve in the test rig with a new one and retest,as stated testing the car warm is prefered vs. testing it cold. Though a leakdown test is still a much more accurate assesment of engine condition. |
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