rover 3.9 compression

[bin looney]

just done a compresion test on all 8 cylinders got a reading of 145psi on all cylinders is this correct for a 3.9 v8?

[GreenV8S]

Smidge on the low side but reasonable. If they're all consistent to within say 5% that's an extremely good sign - consistency is more important than the actual value in terms of checking for engine wear/damage.

[P100]

Hi,
You would ideally like to be around 165 psi to get as near to the manufacturers figures.
Anything less than 140 and you should be considering a rebuild, or at least a new set of rings to help restore the compression.

Remember that you will loose power and performance with low compression readings.

Cheers Roy

[astonman]

Do you have a standard cam?A cam with more overlap will give a lower reading.

[bin looney]

i have a piper 285 ultimate road cam.
engine runs well, been rebuilt by me recently, but its running warm so i am going through a few checks.
timing is an issue, supposed to be around 4 btdc but its no where near which is a poser.
i know there are different front covers, mine is off a sd1 onto a range rover 3.9.
going to have a good look saturday.
check my car out on utube.

http://uk.youtube.com/watch?v=b_ybhc9sYJQ

[GreenV8S]

bin looney said:

supposed to be around 4 btdc

Really, is that all? I'd have thought you would be looking for much more than that, particularly since it doesn't seem to be a particularly high CR. Perhaps you have a dizzy with an unusual amount of mech advance, but I'd have thought you want to be around 28 - 32 degrees all in. Remember that the timing marks on the front pulley aren't reliable unless you've verified them.

Edited by GreenV8S on Friday 31st August 23:45