The leak down tester includes two gauges, a regulator, a port for connecting to an air compressor and a port for connecting into your spark plug hole.  Testing with a leak down tester is similar to a compression test, but the position of the cylinders is critical to getting valid results.  In general the piston should be at top dead center on the compression stroke.  You can also test leak down with the piston at bottom dead center, but most consider top-dead-center to give the most valuable results.

A typical leak down test kit:

The first step is to warm up the engine to normal operating temperature.  This is done so that the rings have expanded and hence will seal better, and should give more meaningful results.  This is not absolutely necessary, however, and the test can certainly be done with the engine cold.  The test results will not vary (in my experience anyway!) all that much.
Next, remove all the spark plugs.

How to position the engine

After the spark plugs have been removed, you can position a piston to top dead center by taking a thin, long screw diver and putting it into the spark plug hole.  If you have a manual transmission, put the car into top gear (5th gear in most cases), and release the brake.  As you move the car forward, or backward you can watch the screw driver rise and fall.  After the screw driver reaches the top, and just begins to fall, put on the parking brake.  Screw in the test tube into the spark plug hole, and run the test.  If you have an automatic transmission, I believe your only option is to turn the engine by hand.  This can be done by turning the crankshaft pulley with a socket wrench.

To run the test connect the regulator end of the tester to an air compressor.  Adjust the air compressor to at least 100psi.  My own compressor goes to 120psi, and that’s what I use.  Adjust the regulator so that the left gauge reads 100psi.  If you hear a lot of air coming out, and the right gauge reads very very low (like 40psi or less), chances are that the engine is in the wrong position – that is – it was on the exhaust stroke instead of the compression stroke.  Remove the test tube, and move the car again so that the piston drops and comes back up to top dead center again.  Re-install the test tube, and adjust the regulator to 100psi.  If the right gauge reads 90psi, that means you have a 10% lead-down.  If the right gauge reads 95psi, you have 5% leak down (time to celebrate!).  According to sources, anything greater than 15% indicates excessive leak down, and repair should be done.  If you listen to where the air is coming out of, you can hopefully determine this repair.  Make sure that the leak down test tube is sealed well in the spark plug hole.  I had to get a better O-ring for the kit, and I actually super-glued the end of the test pipe so that if I tuned the rubber part of the tube, the threaded end would turn as well.  This allowed me to get a better seal in the spark plug hole.

The following was taken from the following website (Walt Osborn):
http://www.morrowmarsh.ca/concours/techpages/leakdowntester.htm

“Listen for leakage at the following places:

* Adjacent cylinders sparkplug hole. Use a piece of small rubber vacuum hose, stick one end near the spark plug hole and the other end in your ear. Leakage, air hiss, heard here may be a blown head gasket between cylinders or it may be leakage heard through an open valve.
* Exhaust pipe. May indicate a burnt or stuck exhaust valve.
* Carburetor or throttle body. May indicate a bent or stuck intake valve.
* Oil filler or dipstick hole. May indicate broken rings or a damaged piston.
* Radiator filler cap. Bubbles here will indicate a leaking head gasket or cracked head.
”

Repeat the above steps for each cylinder, record the numbers, and check the above locations for air.  If the numbers are suspect, you might want to run the test again with the piston close to bottom dead center.

Put the back of the car on stands. You will absolutely need a trolley jack later in the procedure, so don’t even dream about trying this with only the emergency jack. At some points, when you’re hauling and shoving at things down there, you’ll be very glad the vehicle is secure.

Remove the rear and center shields (aka: diapers). Note which fasteners are screws and which ones are poppets, as they are just as much fun to refit as they are to remove.

Here’s the rear mount. Easy to get to, easy to remove. Before you unbolt it from the frame, pad your trolley jack saddle and place it beneath the bell housing. You don’t want to lift the motor, you just want to fully take its weight off the mounts.

And here’s the front mount. You’ll have just barely enough room to get to it. Keep your tools at arm’s reach. Unlike the rear mount, with its four bracket bolts, the front mount only has three. That’s the good news. The bad news is that only the lower center is easy to get to. The others require patience and good tools. I’ve circled all three. The one you can’t see is the one that will test you.

I recommend doing the mounts one at a time. You could do them both at once, but if you slip out of alignment, you’ll need friends to help horse the motor back into position. So first I removed the rear mount, and cleaned it thoroughly. That’s the editor way.

Here’s the rear inserts snapping into place. I lubricated the inner part with WD-40, to aid in fitment and hopefully give myself a bit of relief as the mounts resettle. WD-40 will disipate eventually, so I thought this a wise move.

Have your assistant (no photos, I was under the car!) give the jack small inputs until the center holes line up, then shoot the center bolt home. Torque the bracket bolts to 38 ft/lbs, torque the center bolt to 66 ft/lbs.

Here’s the troublesome bolt on the front mount. It actually goes in the other way, but I thought you’d like to see the position. Reinstall the mount, double-check your work, and wipe down and clean and lubricate all the parts you have access to down here. This is a great opportunity since the shields are off and you’re down here anyway. As always, I was pleased to note the general cleanliness and good operating condition of my Spyder.

Driving impressions: No vibration on startup. A good sign. I began to experence some faint vibration or buzzing when launching out of first, and in engaging second gear on rolling starts. It could be worse, but I’m pretty well braced up already with Corky’s and Che’s. A rear STB would probably help. Once into third and beyond there are no vibration effects. In first and second, there’s now no lag on throttle – the accelerator pedal instantly pushes the car forward. Nothing extreme here, but a general sense of things being tightened up and more solid-state, more fly-by-wire. I suspect my 0-60 time is slightly improved. I may add more comments later after the mounts break in fully, a period I expect to take between four to eight weeks, depending on much I get to run the car.

PITA factor: Minimal, maybe two brewskies. Aligning the front mount bracket bolts took a long time, as it was difficult to force the polyurethane blocks through the bracket. I used a screwdriver through the center bolt track to horse the mount up and down, side to side, until the bolts finally seated.