Compression

[tehwickerman]

I decided to do a compression test on my M20... got around 155~157 on all cylinders. Bently said it should be 140. Anyone know if my compression is high or if Bently is just wrong?

[jlevie]

Those are reasonable numbers. Have you done a leak down test? It will tell a lot about the condition of the cylinders and rings.

[nando]

it's going to vary engine to engine, depending on how much carbon deposits there are, how the rings and valves are sealing, what the weather is like, how long you crank it, etc. etc.

the important part is they are all close to each other. sounds like you are good to me.

[tehwickerman]

Good stuff, thanks for the input.

[Knockenwelle]

Bentley numbers are a service minimum. Lower than 140 indicates problems.

[strad]

I decided to do a compression test on my M20... got around 155~157 on all cylinders. Bently said it should be 140. Anyone know if my compression is high or if Bently is just wrong?

Last time I looked, I remember bentley giving a range between 142 and 156 for all engines covered by the E30 manual. Dunno where you got 140. Also, you must account for altitude when you do a compression test (see "time to rebuild" in pelican's technical articles.)