Hi, I am getting exhaust manifofdls replaced on my engines and a compression test shows the readings are quite varying on the cylinders. The mechanic doesn't think it's worth getting the heads removed/done at these readings but what do you think? - we are pretty certain it's the valves not pistons/.rings causing this as one head had to be romoved last year to replace abroken valve and the valves were 'slightly' pitted..

Port from 1 to 8: 160,150,160,130,135,100,140,110
Starboard from 1 to 8: 135, 160,140,140,150,140,100,110

I don't really want ot spend the $, but could these readings cause any long engine damage or anything? - what would you do? They are 2 merc 5.7L 260hp magnum 1988 fresh water cooled engines with approx 550hrs.

I look froward to hearing peoples thoughts/opinions on this....

Never do a top end without doing a lower end.

Squirt Some Oil In The Cylinders And If The Comp Goes Up The It Is The Rings If Not Do A Valve Job And See What Happens.

You could do a leak down test. The tool is cheap to buy and you could know if it is piston or ring problem, or an intake valve problem, or even an exhaust valve! I'd do this before opening anything.