Compression check results - are they acceptable.......

[Jimmy]

Undertook a compression check of all cylinders (2.0L 911), all were 150 PSI with one being 140, the engine was hot(ish) at the time of testing. I believe this to be acceptable though cannot verify as I haven’t any data from what a new engine would produce. I am attempting to establish the amount of wear and whether it aligns to the odometer reading - 95000 miles, what is the tipping point to when an engine overhaul is req’d?


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Jimmy

[911hillclimber]

imho?
That sounds great to me. Perhaps get it full hot and repeat? Check the valve clearances on the '140' cylinder?

fwiw: my 120K mile 3.2 engine, never been apart, hot, has numbers in the same range and runs like the Star Ship Enterprise.

[haasad]

They are fine but as Graham says check the valve clearances on the lower one.

My high comp 2.8 has 178 to 180 psi on my gauge, hot, wide open throttle

[911hillclimber]

Now, there's an interesting thought!

I have a simple Guyson/Gunson Comp tester with 150 psi rated as 'Max Green' At 160+ it is in the red, at 100- it is in the red.

I have recently used it on my race engine (3.2) but cranked the engine with all plugs out bar that being tested and cranked for 5 seconds, about 3 'firing' strokes BUT with the throttle closed.

Does the throttle being wide open (to swallow as much air as possible) make a big difference Andy? I have not read that before.

I'll have to give that a try this week.

Reason I say this (and I hope this is of interest to OP) is that I got 5 cylinders @ 100 psi and #6 cylinder at 200psi before I found a huge air leak in the manifold gaskets on #6.
Results were repeatable.

[Jimmy]

The garage had performed a pressure test of the bores prior to start up (remembering the car hadn’t been cranked or started in many years) and the results were very poor. The lesson learnt (for me) is not to form a diagnosis unless all required tests are complete. Am very pleased with the results

Thanks for the update (Andy / Graham), much appreciated.

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Jimmy

[haasad]

Not sure what difference if any wot makes, I was taught to do it that way with plugs out to take load off the starter. Never done it differently.

Glad the op is happy with result.

[Cortina]

Now, there's an interesting thought!

I have a simple Guyson/Gunson Comp tester with 150 psi rated as 'Max Green' At 160+ it is in the red, at 100- it is in the red.

I have recently used it on my race engine (3.2) but cranked the engine with all plugs out bar that being tested and cranked for 5 seconds, about 3 'firing' strokes BUT with the throttle closed.

Does the throttle being wide open (to swallow as much air as possible) make a big difference Andy? I have not read that before.

I'll have to give that a try this week.

Reason I say this (and I hope this is of interest to OP) is that I got 5 cylinders @ 100 psi and #6 cylinder at 200psi before I found a huge air leak in the manifold gaskets on #6.
Results were repeatable.

Throttle open (normally !!) makes a huge difference ... it's the "right" way to do it (read compression tester instructions )
prove it to your self - test both ways and look at results