glen242

Instructions that came with the cylinder leakdown tester I bought from Eastwood say to remove all spark plugs, put the car in neutral (4 speed) with the hand brake on, run the piston up to TDC on the compression stroke, and put the air to the cylinder.

Seems to me, if I do that, the air pressure will force the piston down to BDC, and since the exhaust valve opens @ 68 degrees BBDC and the intake closes @60 degrees ABDC, all I'll get is a lot of air going out through a valve. Am I missing something here?

john73bb

I just did this on another car. You have to make sure the engine does not turn over as you are applying the air. It doesn't put a lot of pressure on the top of the piston, but is is enough to turn the engine over.

American Boy

If you are right on the TDC, it won't move but if you are a little off to one side or another, it will spin the engine.

Stephan

woodworkr

If I am not mistaken, once you get the cylinder filled you listen to see if you hear air. If the air is comming from the carb it is an intake valve that is not good. If it is comming from the exhaust then it is an exhaust valve. Can someone correct me on that.
JoeB

john's '81 mouse

After you get the cylinder to TDC, then simply put the transmission into gear before you apply the air pressure, and perform the test on that cylinder. Write down the readings, take the transmission out of gear, and move on to the next cylinder and repeat until you've done all 8.

Wrencher

If it's right on TDC, it won't turn. The in-gear trick works, and I've used a long breaker bar to hold the crank when I get lazy and don't want to deal with it rolling over. This is by far the best way to check combustion chamber integrity.

Hans

71coupe

If you do a leak down test on every cylinder it will take you forever.
When I worked at a dealer, I would do a compression test first. If I found any low cylinders, I would then install my leak down tester on the bad cylinders.

Note: if the motor has a lot of miles it will be hard to keep the piston at TDC.

gkull

I haven't given it much thought in years. I do remember in training you would do a mid cylinder measurement and it could potentially tell you if your thrust face of the hole was out of round if the % of leak was worse than TDC or BDC

Now I just hook it up to a warm motor and a don't care where the cylinder is. Your looking for what ever you call an exceptable %

glen242

Thanks for everyone's input. I'll probably put it in gear to make sure the crank does not move too much.

I plan on starting with #1 @ TDC on compression stroke, then rotating the crank in 90 degree steps and doing each cylinder based on the firing order. Is this the correct way to do it?