Compression gauge question

[Roadster90]

Recently Padgett provide a list of tools that we should aquire. Among them were a simple compression gauge which I bought...think the thing was only 10.00...

Question: Harbor Freight now has the below gauge (40.00 piece of equipment on sale for 25.00) on sale and am wondering if this "leak down" gauge is better or more desirable please....comments please?

Thanks,,

Nic

CYLINDER LEAK-DOWN TESTER

Quickly diagnose problems with pistons, rings, and valves. Cylinder leakage gauge makes it easy to conduct leak-down tests--more accurate than standard compression tests.

For all domestic and imported engines

Easy-to-read gauges for proper testing and accurate results

Easy-to-adjust regulator

Will work on vehicles with low clearance

0 to 100 PSI working pressure

Comes with pressure gauge, cylinder leakage gauge, spark plug adapter, quick connect/disconnect hose and regulator.

ITEM 94190

[padgett]

I have one and it is a fun tool but am not sure what it tells you that a compression test wouldn't.

Basically you hook it up to an air supply, set the static pressure, and see how much air it takes to match it when connected to a cylinder.

Not sure if I did it right, the instructions and what I found on the web were almost unintelligable and make no sense (set leakage guage to zero. Read leakdown on gauge). The crank does need to be positioned so that both valves on the cylinder being tested are closed.

If someone knows the right way to use (what I did was to set to zero with the output blocked then leave the adjustment in the same place and see what each cyl read looking for same-same rather than any particular value) please let me know.

[harry yarnell]

A 'leakdown test' is a very good diagnostic tool. It allows you to determine how well a cylinder is sealed. All engines will leak to some degree; the smaller the better. leakage occurs at the rings, valves, holes in pistons, and headgaskets.

You pump in air into the cylinder and time the leakage to some low arbitrary number. Compare each cylinder. This, of course requires the valves to be closed, so there's some monkeying around to get each cylinder to TDC.

With a compression test, this isn't necesary. But the idea of a leakdown test is to pinpoint WHERE the leak is occuring, so you know what corrective action to take.

[Ronnie]

Just a reminder to anyone who has not done leakdown testing before.

Leadown testing should be done with safety in mind. Applying high pressure to a cylinder a few degrees off TDC can cause the engine to turn unexpectedly when the pressure builds up and overcomes internal friction/resistance of the engine. Injury can come from tools (such as socket and rachet) used to turn the crankshaft or hands caught in belts while trying to turn the engine.