compression test P 6..??

[RICCO the TRIKE]

hi guys ..

doing a compresion test on my P6.......
what readings should I expect..????

TA ...

[DaveEFI]

hi guys ..

doing a compresion test on my P6.......
what readings should I expect..????

TA ...

The quoted figures are only a guide as there are so many variables. What you do look for is them all being within 10% or so.

[RICCO the TRIKE]

ok .....

so would this be ok

psi ....50 50 50 30 50 30 30 50.......

or should they be higher ???

[kiwicar]

Not really because three of them are 40% below the others. . .
Without knowing static compression and cam timing figures it is hard to say beyond that, however assuming hat we are not looking at an 8.13:1 compression unit that someone has fitted a 300 degree advertised duration cam to I would say they are all pretty low. I would expect 75 to 130 PSI range, but that is real finger in the air stuff with no motor specs.
Put a squirt of oil dowm each bore and try again noting the new numbers against the figures just posted. If they increase on average more than 50% or any one increases by 100% then I would say with some confidence it needs a rebore and re-ring minimum and really a rebuild would be a good idea.
Actually as it is a P6 would you not be better off just looking for a 3.9 lump to rebuild?
Best regards
Mike

[DaveEFI]

ok .....

so would this be ok

psi ....50 50 50 30 50 30 30 50.......

or should they be higher ???

It's most unlikely all the compressions will be very low on a running engine. Bores and pistons don't wear out evenly - and valves usually fail individually.
Then there's a question as to how you do the compression test, and how good your tester is, and how fast the engine cranks. If you must have a ball park figure, 130 is it. Slightly higher if an early P6 engine.

[Ian Anderson]

When you were doing the compression test did you hold the throttle max open?

If not the engine cannot draw in enough air to make the compression pressure correct!

Ian

[unstable load]

and how fast the engine cranks.

This is important along with the wide open throttle.