Hope you can stand another "compression test results" thread
Thanks for the info! Much appreciated. Question...how exactly does a leak down test tell you if a cam or head is bad? I understand that if you have a poor seal on an exhaust valve you'll hear a "hissing" sound but that's about all I know.
An LD test will tell you what is, or is not, leaking. By itself it cannot tell you if your cam is bad. But,
if your LD test shows no obvious leakage, then together with your compression test results; the low pressure cylinders by default, have to be caused by either; 1) the valves were not opening for as long as the others , or 2) the compression test was not done quite right.
Too often the compression test is run for an arbitrary number of cycles, instead of until the highest pressure is recorded at least twice in a row.
On a good engine, peak pressure will be observed within about three, mayber four cycles. But if the cylinders are dry, it may take many cycles. Or if the valves are sooted up, the results will be erroneous. Sometimes, in the past, I have had to remove the rocker arms/shafts and smash the soot off the seats by tapping the valves with the cylinders pressurized, which will; 1) get the pistons out of the way by blowing them down to the bottom of the cylinder, where, hopefully, the best part of the cylinder is, and 2) blow the soot off the seats. When tapped in this way, sooty seats sound different when the valves land, than clean seats do. It will be obvious.