compression test

[Serge914]

I just did a compression test today on my 74 1.8 and got those results: 95-105-90-110. The two low readings are the back cylinders. The engine was warm, I am using a screw in type tester and was cranking the starter 8 revolutions each time. Should I worry ? Any chance adjusting the valves will help ?

[Kevin@ojai.net]

My limited experiences with doing compression tests on these things say YES. I overheated my engine pretty badly a while back, and had something like 40# on number 4 (#4's valves were completely tight). After I adjusted the valves all the way around, I redid the comp test, and all 4 cycls were pretty close to each other again. (I forgot to right down the numbers, so I cant tell you what they were, but #4 still was a little low).

Hope that little story helps,

-Kevin

[Dave at Pelican Parts]

A difference of 20 PSI isn't too bad. But the low number being 90 would make me worry. Very very definitely adjust the valves and re-check.

The numbers will read significantly lower if you are at high altitude. If you're in Denver, for instance, your numbers might not be so bad.

If the numbers don't improve with a valve adjust, I think I'd see if I could get a leakdown test done to see how much leakage is happening, and where. To find out where, you listen for hissing. At the intake snorkel means the intake valve isn't sealing, at the tailpipe means the exhaust valve isn't sealing, and at the oil filler means the rings are leaking.

Might be time to start saving for that rebuild....

--DD

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Pelican Parts 914 Tech Support

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[scriabin]

--Don't forget to have the throttle FULL OPEN while testing. At least, it's something I've forgotten before, causing significantly lowered readings.