compresion versus leak down test what's the diff

just had my 1966 200 ci motor rebuilt,,,,, cylinders 2 thru six all have approx 170 lbs. on the compression test,,, cylinder 1 has only 135 lbs. sounds like an issue to me,,, the mechanics ran a leak down test on all cylinders and they all came in at roughly the same numbers.... don't remember what they were,,,,what gives,,, is it because their two different kinda tests or what


thanks for any help or info

8) a compression test tells you how much cylinder pressure is available, where as a cylinder leak down test lets you know how much cylinder pressure you are losing. for instance, lest say your compression tester indicated that you have 150psi available, and your leak down tester indicates you have 10% cylinder leakage. if you could get 0% leak down, you would end up with another 15psi cylinder pressure available, which makes a substantial difference in combustion pressures when the engine is running.

Leakdown test is checking the sealing of the rings and valves.

Good article on leakdown testing here: http://www.carcraft.com/techarticles/11 ... ewall.html

Apparently you need to do some listening and poking around during the leakdown test to get some real answers.

How long since the rebuild? Depending on the type of rings, they may not have seated if it's *just* been assembled.