People recommend it for cars that burn oil and smoke. What is it, how is it done, cost, etc...??? I searched but its not working, so Im just looking to see whats involved w/ this.

 

well, to burn oil, oil must get into the combustion chamber. negating the possiblity of it leaking from the top end (bad valve seal for example), it will have to come from the bottom....meaning it would have to get past the piston ring. now, i dont know for sure, but im guessing its to test the seal of the rings.

that being said, i have no idea how its done

 

A leak down test is essentially a more complex compression test.

It involves screwing a special tester into a spark plug hole, setting that cylinder at TDC, locking the motor, then connecting an air compressor to the leak down tester.

What the tester measures is the rate at which air "leaks" down through the engine. It's kinda cool because sometimes you can hear exactly where the compressed air is escaping and immediately identify your problem.

It can test for a lot of things including cracks in the block/head/water jacket, messed up rings, messed up head gaskets, etc.

 

As you listen from where the air is leaking from and at what rate it is. That will tell you where you have a problem and what health the engine is in. Usually you don't want to see any wrose that 10% leakage or 10% difference between any of the cyl.

If you hear the excessive air from the crank case, your Rings are bad, cracked cyl/head, etc. If you hear if from the intake, bad valves. If it is coming from the valve cover and from the area of the springs.. it most likely is the valves and/or seals.

I had about 5% or less from my 99' LS1 take out.. was in good health and prove to be a good runner once I got it running. But from the test, I had good reason to beleive that the engine was going to be good.

 

Thanks for the fast responses guys. Makes sense now. Is this something I need to let a "professional" do? Like at a shop or something. Or can I get a tool and do it on my own?

 

I like to test at BDC also. That way if it is something like a cracked cylinder wall it will show up.

 

You should be able to buy the tool or rent it.. you just need to find a good way of locking the crank from rotating at TDC/BDC.

I was lucky to be able to do the test with my engine on a stand and not in the car..made it easy to pull the plugs, put he air adapter on and also lock up the crank/flywheel at TDC.

and you will need a Air Compressor that can do 90+ psi (or 100+).

 

Sounds like it might be something I need to let someone w/ experience do...

Thanks again for the help. I might just change valve seals first and see if that solves the smoke issue.

 

In a manual can't you just put it in gear?

 

Yes, Putting it in gear and blocking the wheels will do the trick, providing your Clutch doesn't slip. There is usually a bit of movement between the gears, rear, u-joints, etc.. but if you get it right, the crank will stay put long enough to get your readings.

 

Can any shop perform the test?

 

Huh, I never thought of doing at BDC as well, that's a good point.