engine and drivetrain Compression test result. Need opinion.

[KC]

Hi there,

I just bought this 1976 BMW 2002 a couple weeks ago. Sorry no pictures yet. The car was sit for couple years. This is what I did so far.

- Drained motor oil and fill up with fresh one

- Flushed all coolant hoses and radiator, filled up with fresh 50/50 and bled the system.

- Drained old fuel and fill up with fresh one

- Changed fuel filter

- New battery

And then it started right up. After that I let the engine cool down and did the compression test. Here is the result

Cylinder#1: 60 90 100 110

Cylinder#2: 60 80 85 90

Cylinder#3: 60 90 95 100

Cylinder#4: 70 90 100 105

All your opinions are welcome. Let me know what you think. TIA.

[M2M3M3]

how long did you let it run for before doing the test? was the engine fully warm?

did you hold the throttle wide open during the tests?

those numbers are really low.

[Cameron]

Hard to really say anything other than that the numbers are low, but pretty even. How does it run? Does it smoke? And was this done with the gas pedal to the floor? How did the plugs look?

[Chris_B]

So, what were the conditions that yielded the 4 different numbers for each cylinder?

These numbers are quite low and the delta between them is not great either.

You may want to run this motor for a while (say, several hundred miles) to let things loosen up a bit and then retest.

[oldguy]

your compression gauge reads low.. your motor is fine across the board but a little long in the tooth if you can dry your hair if you remove your oil fill cap

[KC]

I tested it when engine was cold. Do I need to do this when the engine is fully warm up?

[Chris_B]

yes.

[KC]

OK. that's explained it. I will re test again tomorrow with fully warmed engine.

[TobyB]

The car was sit for couple years

Drive it for a month and try again. Compression tests

(especially cold) on an engine that hasn't been running

just aren't indicitve of much.

t

[KC]

I re tested this time with fully warmed engine. I got same number across all 4 cylinders.

60 90 100 110

So far, no white or black smoke that I notice. Engine still has good power.

Not sure what to look for at this point. All comments are welcome. TIA.

[Chris_B]

Check your valve adjustment. If you want to investigate further, have a leak down test done. Otherwise, do what several people have suggested- drive the car for a while and then retest. If you don't have coolant in your oil and the motor runs OK, it isn't worth having a lot of angst about this.

[kbmb02]

I re tested this time with fully warmed engine. I got same number across all 4 cylinders. - 60 90 100 110

Low static compression numbers like that could also be due to your engine having a camshaft with lots of overlap (or, perhaps a gauge which is not calibrated).

A leak down test (warm engine, quiet garage) will provide additional information about the condition of rings, valves/seats, etc.

-KB

[KC]

I think the timing might be slightly off too. Does timing have any effect to compression?

[Chris_B]

You are probably referring to ignition timing and no it does not have any effect on compression.

[williamggruff]

I think the timing might be slightly off too. Does timing have any effect to compression?

No, timing should not have any impact on compression. You're removing the spark plug to take the compression measurement.

If, however, you believe that the timing chain may have skipped a tooth, thereby changing the synchronization of the camshaft timing with respect to the crank shaft, then yes, it could have an impact on compression, as your valves would be opening out of synch with piston movement. While it's possible that this has happened, it's pretty unlikely.

As others have suggested, performing a leak down test in a quiet garage will help you diagnose whether and where your compression is escaping.