DIY Leak Down Testing?

[yo911]

Sorry if this has been asked (I'd assumed it would have been) but I couldn't find anything after performing a search. If there is a thread, please post the link.

I'm looking at trying to DIY leak down tests. Some of the places where used 911s are located don't have reliable shops nearby, so hence the need for a DIY test.

Seems like a dual gauge tester would be more accurate then a single gauge.

I've read a few articles for general leak down testing, but nothing specific for a 3.2 Carrera.

Specific questions:

Quality testers at a reasonable price?
Any specific order to follow?
Specific sequence?
Acceptable readings?
Paths of leakage to listen for?
Specific tools of the trade (stethoscope-type device, or ?)?
Ways to find TDC?

Any advice appreciated. Mahalos, gentlemen!

[lucittm]

Yo,
I built my own leakdown tester from plans I found on the Internet.

I use a dual gauge but that makes no difference for accuracy. The first gauge just shows you the supply pressure. It keeps you from having to run back an look at the gauge on your air compressor to make sure you are at full pressure. Having matched gauges can be nice though, especially if they are both calibrated. Make sure the reading you are looking for is in the middle of the gauge range, that is where the gauges are the most accurate.

There is nothing specific about your car except the way you check the cylinders. Position the pulley for TDC (Z1) and check cylinder #1 (if you get a zero reading on the leakdown tester then the cylinder is not on the firing stroke, it is on the exhaust/intake stroke and you have to go around 360 degrees to TDC (Z1) again), take your measurement and then rotate the pulley 120 degrees and check cylinder #6, then rotate the pulley another 120 degrees and check cylinder #2 and repeat this for #4, #3, and #5 (firing order).

I used the hose from my compression tester because it had the correct spark plug fitting on the end. Be sure to remove the one-way valve if there is one in your hose.

I never did find a commercial-grade tester in my price range. My parts cost me $50. The gauges don't have to be perfect because you are looking for variation mostly. Now the regulator has to be a good one, not a cheap in-line paint sprayer regulator. I used a Norgren regulator. Just expect to pay $25-$40 for a good one.

If you use 50 psi for supply pressure, expect 40-45 psi on the output for a typical engine (cold). This would equate to 80%-90% of the supply pressure (or 20%-10% leakage). A newly rebuilt engine would show 45-48 psi (10%-4% leakage). Racing engines have 1%-2% leakage.

If you use 100 psi for supply pressure, just double the above. Also, be careful that you are exactly at TDC and the car is in neutral with the brakes set because 100 psi can cause the engine to rotate.

I check TDC with a dial indicator but you can use a thin dowel. Mark it at the point of furthest travel away from the centerline of the engine referenced to a handy surface like the top of the cam tower. Always turn the engine over by the fan pulley though, not the starter. This will take two people of course.

If you detect leakage, place the compressor in the driveway and close the garage door because you need to hear the faintest sounds. If the air is hissing in the exhaust, you have an exhaust valve leak. If the air is hissing in the throttle body (open the butterfly) or air filter, you have an intake valve leak. If the air is hissing in the oil tank or air filter breather hoses, you have worn piston rings. Chances are there will be more than one path.

Good Luck,
Mark

[yo911]

Hey, LM.
Thanks, I just saw your post now.

So, how "hot" does the engine need to be? Seems I can get burned. Is it okay to remove the plugs when the engine is hot? How easy/hard is it to remove the plugs? Should the car be raised on a lift? Sorry for the simpleton questions, but I've not worked on Ps before.

[sailchef]

The tolerances of engine parts will be closer on a "hot " engine because of expandtion and will give you better numbers. A "warm" engine is good, "hot" is better.

I just purchased a Leak down tester from Harborfreight.com. $29.95 + shpng. It has two guages, adapters for the plugs and looks to be made very well. I havent used it yet so cant say anything about that.

good luck with your project.