Bring on the Compression Guru

[st0878]

Alright you propeller heads.... Here's the dreaded compression numbers from my 75 Z with 173k. I did the test with all the plugs out and a preheated block. First the good news, I blew even numbers across all cylenders. The compression dry was 130 on all 6 and 140 with 2 squirts. I didn't think that a 10 PSI jump wet was a great jump (correct me if I'm wrong) so I was wondering if there is anything else that could be causing low compression like the valves? And without looking inside would you think that a simple honing and rings would fix this? The car seems to have OK power and no valve rattle.:disappoin

[2ManyZs]

A 10 psi jump by putting a small amount of oil in the cylinders is a fairly significant jump showing that your rings and/or cylinder bores are worn.

The valves and/or associated hardware are probably contributing the most as far as compression loss. It could be the valves themselves, valve seats, weak valve springs, adjustments way off or any combination of the above.....

130 dry is getting pretty close to what I would consider time for a rebuild. You could do a compression leakdown test to determine where the worst of the loss is. Pressurizing the cylinder and listening to the air trying to escape and where it is coming from will tell you where the worst area is, either rings/cylinders or valve/head related. Air loss will be most noticeable through the intake/carbs/throttle body if the major damage is in the head/valves and air escaping through the rings/cylinders will be heard by listening to the oil fill on the valve cover.