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