Steps for accurate leak down test

[ARCSinAK]

I am interested in the steps involved performing a leak down test. Anyone have info or a link to a thread that covers the proper procedure. I am struggling with the timing on number one cylinder of a 70T which did not run for a number of years, trying to rule out a possible corroded valve and determine the over health of the motor. She had a newer valves and full split case new P/C rebuild 8 K before she was parked. Took about 7 months but she running 1K miles so far pulls strong to 6K but just want to make sure I have good leak down numbers. I have access to a quality leak down tester but have never done the test before. Thanks for your time.

Regards-

JS

[rennworks]

JS, pull all the spark plugs. Put it on TDC on #1 pressure it up, note the reading. Turn 120 degrees (there is a mark) do #6 and so on through the firing order. If you are unsure if you are on tdc on 1 or 4 pull the dist cap off and see which wire the rotor is pointing to.
Warren

[James Brown]

the first step is a quality tester. the gauges should be calibrated by a good shop first. here is one i found on amazon OTC 5609 Cylinder Leakage Tester Kit : Amazon.com : Automotive

[911pcars]

google.com is your search friend.

"cylinder leak down test procedure"

Take your pick from 141,000 hits. I previewed this one and it's just okay.

How To Perform A Leak Down Test - EricTheCarGuy - YouTube

I've found that many low-cost testers (as used in the above video) suggest a relatively low 35psi or so as a reference source pressure, perhaps as a safety precaution to prevent the engine from moving if the piston isn't exactly at TDC. The better gauges I've used suggest using 100psi - makes it easier to hear leakage from crankcase, exhaust, intake, radiator (water-cooled engines), etc.

A procedure from Snap-On or from a major tool manufacturer will be most valid. PM me for a doc with an adapted Snap-On procedure.

Sherwood

[al lkosmal]

DIFFERENTIAL CYLINDER PRESSURE TESTER MODEL E2A from Aircraft Spruce

I like the leak down tester(s) from aircraft spruce.

regards,
Al

[James Brown]

one thing you have to look out for is the size of the hole or orifice the air goes through. different engines (as in aircraft) manufactures require different orifice sizes. No idea what Porsche requires or recommends but that should be checked first.

[James Brown]

found this discussion differential compression testers

[911pcars]

Originally Posted by James Brown

one thing you have to look out for is the size of the hole or orifice the air goes through. different engines (as in aircraft) manufactures require different orifice sizes. No idea what Porsche requires or recommends but that should be checked first.

I think the orifice provides a constant but reduced volume of pressurized air to the test cylinder so the air compressor doesn't have to cycle and resupply volume as might happen on an especially loose cylinder test. My guess is that a larger bore/combustion chamber (e.g. Lycoming bore is 5.125") may require a larger orifice than a 3.5" or so automotive cylinder. The orifice might also allow the gauge needle to remain stable and not flutter/fluctuate as much. Another reference point: one of the YouTube, DIY LD builds suggests a .060" orifice.

FWIW,
Sherwood