Can anybody tell me how to do a leak down test? I got the tool from Harbor Freight, but I can't seem to figure out how to use it. It has two gauges. One has 0 - 100 PSI, the other has 100 - 0% graduations on it. The instructions are rather ambiguous.

From what I understand, you remove the plug, put the cylinder into TDC, then connect the lead hose to the spark plug hole. Then connect the tool to the lead hose, and turn on the air, and turn the regulator until you get the differential gauge to read 0%. Then what??? Turn it off? Disconnect the air?

Somebody help me please! This thing is making me go nuts!!! :confused:

You send air at 100psi to the cylinder nonstop. The cylinder will leak a bit, meaning that it will never quite reach 100psi. The other gauge will either read "percent lost" or "percent filled". If it reads 95%, then it's safe to assume that means 5% leakdown. If it says 5%, then you can assume it also means 5% leakdown. Expect some leakage no matter what.

A leakdown test is way better than a compression test because it cuts out so many variables, such as how powerful the starter is, or what the cam is like. I've never done one myself, but I do have powerful dreams about it.

Good luck, report back.

Do I run the pressure up to 0% on the differential gauge while I have it attached to the cylinder, or do I run it up first and then attach it?

Here ya go - Google is an amazing thing.

http://www.carcraft.com/techarticles/116_0406_cylinder_leakdown_tester/index.html