In continuation to my "Compression Test" thread, I've been studying up on Leak Down Testing. I *might* do this after a normal compression test in a few weeks, if 'needed'.

Let's see if I got it right.

* I should run the engine a bit to get it up to operating temp, etc.
* I go to TDC on #1 and hook up the tester & air.
*The pressure difference between the 'line' and the 'cylinder' shows the overall condition of the cylinder. (7% differential or less is good).
*Then I listen in the intake and exhaust manifolds as well as the cylinder block to see if/where air significant amounts of air is escaping.
* * * any easy methods to do this without dis-assembling things * * * ? Would a stethoscope help?
*Then I turn the crankshaft 1/4 (90 degrees), go to the next cylinder in the firing order and repeat the test process.

Right?

Let me know if I am understanding this correctly.

?? Any tricks to knowing when you are at TDC of #1 'firing' and not TDC #1 'exhaust'? (I suppose I could look at the distributor)
?? Is it 90 degrees I turn the crankshaft, so that I make a total of 2 revolutions to test all 8 cylinders - "a la 4-stroke".

It'll be easy to find out if you're at the 'wrong' TDC, the cylinder won't pressurize at all!


and 1/4 turn is correct, 8 quarters = 2 crank revs...

I've never done this, but trying to hear where the air is escaping sounds like it would tough to figure out. The obvious leaks would be thru one of the valves or thru the rings. If the intake valve is leaking, the air will find its way out of the intake manifold and carb, exhaust valve, exhaust manifold, air past the rings will go into the crankcase and, if the breather hose is off, the air should exit there...I'm just thinking out loud here, but it seems an easy way to figure out which would be to blow some smoke or steam sideways across the carb (would need to be held open of course) or across the breather hose and see if any breeze moves the smoke. Not sure it would work with an exhaust manifold due to the size, maybe if you duct taped all but a small hole over the ends?

I would think that in most cases the air should find its way past the rings, the valves should be the best seal...

anyway...

I would think that if you have enough loss it will not matter where the leak is since it will require at least pulling the manifolds and heads.

what you are looking for is the simple things to figure out. Big loss on one cylynder usually means rings or a bad valve, which you should be able to hear, but if the adjacent cylinder also suffers similar loss it is probably the head gasket.

Whith your compression numbers I would not think you have much to worry about. You may be due for a valve job in a year or so but if it were me I would run it for another season and see how it looks then.

I've never done this either, but getting close to doing it on my '74 TR6.

The only other thing I've read is that (on a car) you can pull the radiator cap to look for bubbles, ala head gasket or listen through the dipstick, ala crank case.

At 100 psi pressure, I interpret that listening for the hiss wouldn't require any special equipment.....

Let us know how it works out, precedure and all....

In my experience, that is correct. Pull the dipstick to hear ring leaks, listen at the spark arrestor to hear intake valve leaks, and the risers or exhaust tubes to hear exhaust leaks. On my race car, it was easy to hear if it was intake vs. exhaust without pulling even the aircleaner, but it had headers, so exhaust was not well shielded.

Be carefull to have the engine EXACTLY at TDC and slowly turn the valve to let the air flow. If not, the engine will rotate quickly...