I am looking for a good Leak Down Tester.
Various brands out there with prices ranging from $30 to $200.
Harbor Freight to Snap On.
Single gauge to dual gauge.

For the non-professional, what would you suggest?
There is a $77-ish version with Summit that seemed good.

I used to sell one (along with other such tools); a buddy of mine makes them and sells them through Summit & Jeg's. I think the Jeg's # is 555-80520.
Retail was about $75.
These had 2 gauges. With input set @ 100PSI, it's easy to calculate %. It's a good product, every one pre-tested/calibrated.

Since I am not working on a pro stock I just made one. Bought a nice gauge and some pipe fittings and used part of my compression tester to plug into the cylinder. Works great and very cheap.

Do yourself a favor and get a two gauge tester....FWIW I have had great service from my OTC leakdown tester for years.

Mine is from Matco tools. It's a quality piece that has worked very well over the years.

The good testers have a correctly-configured orifice, pretty hard to duplicate at home since the orifice size and approach angle are critical.

Interesting, I will have to compare it to a real tester and see how it does. I have mainly used it to compare cylinder to cylinder numbers which I think this one works OK for. I need to check leak down on the new engine and I will compare it to an actual tester. Thanks for the info.

I bought a older Moroso single gauge unit years ago, I still have it but the needle started sticking so I bought a better two gauge unit when I owned a airplane that was FAA approved from Aircrafts Spruce Chief Aircraft supply in Grants
pass, OR supply also sells them
Buy a good one now, not later Good tools should last forever, if taken care of

I have an OTC #5609, very good and not to expensive.

I have found on my 440 equipped E Body with TTI headers that I can only use a leak down tester or compression gauge on about 4 cylinders. I have both screw in adapters and rubber tipped adapters and several different high quality such tools from a variety of vendors. .

What tools have others found that can access all cylinders short of removing headers or pulling engine?

HF one is limited to 15psi. In my opinion that's not enough.


I bought one, removed the first gauge which max was 15psi, plugged it.

Set the regulator to 100psi, and hook it up. Every psi is a %.


Works great.

Old Moroso single gauge unit for me. I've had it for years.

I bought a 2 gauge summit with a built in adjustible regulator about 20 years ago. It has always worked fine.

I think the standard recommended by Moroso, SAE and the aircraft industry is to set the input pressure to 80 lbs and then do the math off of the pressure drop to each cylinder, IE 80/78=2.5%
Don't forget to make sure the gauge you buy and use has the metered orifice to keep it accurate

"In the United States, FAA specifications state that engines up to 1,000 cu in displacement require an 0.040" orifice diameter, 0.250" long, 60-degree approach angle. The input pressure is set for 80 psi, and 60 psi minimum cylinder pressure is the accepted standard."

A lot of automotive testers use 100 psi so the psi numbers represent the percentage...no math required.

Try one from ATS ( aircraft tool supply) They are certified, and can be recalibrated when needed.

Theres nothing wrong with having high quality tools. But not real nescessary in this aplication though. We don't need to prove to the FAA that our engines are good enough to power an airplane through the sky. We just need to know if the valves or the Rings or the head gaskets are leaking. I use 100 PSI in my low cost Summit tester and it tells me what I need to know.

I think the FAA will accept up to 60% leakage and still let you operate the airplane with the proper sign offs
The procedure is different also on aircraft leak down test, you don't test it at TDC, you pull the piston up being tested with the prop to about 120 to 90 degrees BTDC on the compression stroke and have someone read the gauge while holding the prop at that spot
Sometines I will pull a piston up on one of my motors until the valves close to see what the bottom ring sealing looks like

No, we test airplanes at TDC for leak down. The timing is a set thing at what ever degree the engine operates at for testing.

OTC here. works great and not too spendy

continental requirements are based on the service bulletin and requires the minimum be based on an office size for cylinders under 5" bore and a bigger one for over 5" which means an engine can run with 42 psi /80 and meet spec. I also do comp at tdc per ac43.13. Tim

All the A&P that tested my airpalne motor while I watch the leak down tests did it the way I describe, the same answer on the I-A when I ask them about the proper leakdown test
I did end up marking the starter ring gear so I knew where all six cylinders should be at TDC and I did test my 260 HP O-540 Lycoming motor at TDC Those tapered rings seemed to sealed better down lower though
No more hijacking, I'm done

Cab, could you get them to supply some paper work on that procedure, please, so I can know if everybody I have ever talked to has done it correctly. A tapper bore cylinder may require may a different procedure, but not every engine has tapered cylinders. Now that I think about it, I know what you'r talking about. We rotate the engine around to compression stroke and listen for the mag impulse to click, then put pressure to the cylinder, then we move the prop back and forth until it doesn't want to move by it's self before putting full pressure in it. Sometimes you have to move it back and forth some to get the valve to seat all the way.

I wonder what the angle is on holley/eddy jets?

Then he did it wrong IAW AC43.13 1B chapter 8.14 which clearly specifies the test will be performed on warm cylinders at TDC. The procedure is rather involved and has the pressure introduced to the cylinder in stages whereas the average mechanic just introduces 80 psi initially.

A conscientious mechanic will try to achieve the highest reading by moving the prop back and forth at TDC to help seat the rings against the lands, others will simply open the air valve and record the number.

The cylinder leak down test is often called "the A&P mechanic's continued employment test" wherein over 25% leak down is considered a fail.

When the Air Force ran recips they didn't rely solely on leak down tests, they would periodically perform dynamic tests. (You oughta see an 18-cylinder engine with compression gauges plugged into each cylinder...looks like Medusa on a bad hair day)

I visted the Spruce Goose when it was on display in Long Beach, CA, they had a cutaway engine( 28 cylinder corncob radial) on display and was amazed by it The first thing that came into my mind was I'm glad I was never a crewcheif on a airplane that used those motors, epsecially when the flight engineer came in to the hangar and said #4 has a miss in it
I was told by a old time B36 crewcheif that they would swap those motors out in a case like that and then work on them on a engine stand, not on the airplane

I used to crew two DC-3's

they actually had an oscilloscope that was linked to each cylinder via a switch and they watched the pattern from each plug so they could also find bad plugs and cylinders. I worked on dc-6's with R2800 engines. Tim

I was trying to remember the engine designator on them, is it R 4360 ? If not, what size in C.I. where those big motors?

Yes, 4360 Wasp Major often referred to as a "corncob".

https://en.wikipedia.org/wiki/Pratt_%26_Whitney_R-4360_Wasp_Major