7 replies to this topic

[minijoe]

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Any non-standard parts that might be involved with the problem?
hi
can anyone tell me the psi i should exspect when doing a compression test on a standard 1275 / i have 50/45/45/70
many thanks
minijoe

[valve bounce]

you should be seeing 140-190 on each cylinder

[Twincam]

you should be seeing 140-190 on each cylinder

Is that on a high compression unit?

[minijoe]

you should be seeing 140-190 on each cylinder

Is that on a high compression unit?

thanks i,ll take the head off and check gasket it has been useing water lately ,should be able to see any wear in bores at the same time

[Sprocket]

you should be seeing 140-190 on each cylinder

Is that on a high compression unit?

Its a rule of thumb. That means the compression presures should be somewhere between 140 (I would still be happy with 120) and 190psi (Maybe even a little more). What the actual figure is for any given engine wholely depends, not only on the static compression ratio, but, on cam duration and its timing as well.

Edited by Sprocket, 13 March 2010 - 04:47 PM.

[minijoe]

you should be seeing 140-190 on each cylinder

Is that on a high compression unit?

Its a rule of thumb. That means the compression presures should be somewhere between 140 (I would still be happy with 120) and 190psi (Maybe even a little more). What the actual figure is for any given engine wholely depends, not only on the static compression ratio, but, on cam duration and its timing as well.

thanks again
minijoe

[bmcecosse]

Don't understand the figures you quote - they are impossibly low! You need the engine hot - and the (good!) battery fully charged. Take out ALL the spark plugs, and prop the throttle open - brick on pedal, something like that. Then put the tester in each spark plug hole in turn - and crank it for ~ 5 seconds in each cylinder and record the readings. Anything below 140 psi is pretty desperate! It should be 160 psi or higher.

[Sprocket]

Don't understand the figures you quote - they are impossibly low! You need the engine hot - and the (good!) battery fully charged. Take out ALL the spark plugs, and prop the throttle open - brick on pedal, something like that. Then put the tester in each spark plug hole in turn - and crank it for ~ 5 seconds in each cylinder and record the readings. Anything below 140 psi is pretty desperate! It should be 160 psi or higher.

we have had this debate before. You would quite happily condem a perfectly good and serviceable engine, just because it does not achieve 140PSI, which is why any figures given for compression tests should be used as a rule of thumb, unless you have specific information for the exact engine build and even then its still a rule of thumb whith limits.

I said it before, and I will say it again, I get between 120 and 150psi depending on temperature on my 107bhp 16 valver, even on a new build while i used to get between 210 and 240psi on the 1400.

However, there is no disputing that anything less than 100psi needs attention and the OP's figures suggest there is a real problem some where

The important thing with a compression test is consistency of readings across all cylinders and from test to test