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Compression check on 18 magnum.

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John Halper

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Aug 21, 2020
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Atco N.J.
Doing a compression check on an 18 magnum. What would be the average acceptable psi be for one with about 900hrs on it.
 

mgonitzke

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Matt Gonitzke
The service manual (a free download from Kohler's website, by the way) says difference not greater than 15% between cylinders and above 90 psi is acceptable.
 

John Halper

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Aug 21, 2020
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Atco N.J.
Well, Thank you. I was not aware of the free download. So I guess at 70psi I should count this 1 as almost done . Think I try another gauge first . Then give it a squirt of oil or two & see what kind of difference I get.
 

mgonitzke

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For best results, I would do the test with no air cleaner and the throttle wide open. Run the engine first to warm it up. Not much meaning to a cold compression test.
 

John Halper

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Aug 21, 2020
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Atco N.J.
For best results, I would do the test with no air cleaner and the throttle wide open. Run the engine first to warm it up. Not much meaning to a cold compression test.
Need to get running first. Was told its been sitting for years. So as the carb was sitting in cleaner & I was checking other pieces of the puzzle . Its just 1 of the things I did. I am now at , no spark. So something else to chase the reason for .
 

John Halper

Member
Joined
Aug 21, 2020
Messages
16
Location
Atco N.J.
For best results, I would do the test with no air cleaner and the throttle wide open. Run the engine first to warm it up. Not much meaning to a cold compression test.
Warm Or cold . At least it gave me an outlook that the valves were sealing & it didn't have a hole in a piston. Like I said it had about 70PSI in both cylinders. Air cleaner off & throttle open.
 

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