Cylinder compression variances

[Rod Shaw]

Hi

I have just measured the compression on my A7 and found 82, 90, 70 and 80psi after the engine had been run to warm.

I am concerned about a possible head gasket leak but would appreciate any comments before I rush to take the head off. 

Cheers, Rod

[Steve Jones]

They should be the same within a few psi or so, Rod. I think that yesterday's suggestion that you had a head gasket failing might well be correct.

Steve

[Colin Wilks]

Hi Rod,
Have you excluded piston ring problems by testing the compressions with a squirt of oil in the bores?
Have you checked the torque of the head nuts?
Have you checked your valve clearances and that you don't have sticking valves?
I would suggest all these tests would add to what you know about the situation before you pop the head off.

[Rod Shaw]

Thanks Steve.

Cheers, Rod

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Thanks Colin

Good suggestions. Rod

[steve anderson]

Leakdown test is most accurate and revealing where leaks are , rings ,  air in breather ,  valves ,  air in carb. or exhaust , gasket ,  air in radiator , or between cylinders.  I had 10% leakdown , all past rings , will be doing Total Seal rings during Winter teardown .   STEVE

[Bob Culver]

Compression tests done with open throttle.
Gauges did not come into general use until crank handles disappeared. Much can be learned from the handle. Ring  leaks can be heard at the oil filler, and valve leaks sometimes at the carb or exh outlet.
My experience has been that failing valves seem to rob power far more than leaky rings.
Whilst it is a pain to adjust valves, not too difficult to check clearances.

[Rod Shaw]

Thanks all.

Following Colins' check list: The head nuts seam to be torqued fine. Four of the tappets were out by 3 to 4 thou and I have adjusted all to the correct gaps.

However, the "oil in the cylinders" compression test was interesting in that the compressions moved to 88, 82, 120 and 100 compared with 80, 70, 90 and 82 previously. 

After doing the tappets, the figures with no oil moved to 80, 70, 90 and 90. 

Whilst doing this work, I have also noticed that there is quite a bit of wet deposit in the 80 and 70 psi cylinders, even after re-setting the mixture after fitting a new jet body to solve a fuel leak. This makes me wonder if looking at the head gasket possibly expecting damage around those two cylinders is my next step?

Cheers, Rod

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Apologies
Just noticed that the psi figures in last post are all back to front compared with first post. 
Duh!
Rod