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Compression test on an engine that's not in a vehicle


“Airplane cylinders are removable from an engine”

May I assume you’re talking about a radial air-cooled engine . . . ?


Yep Nevada , I’m aware of the ring on the crankshaft & a different cam gear being used before & after 2004 . I didn’t get a chance to try the drill test today on one of my liberty’s . I’m going to remove the plugs & if it spins it spins & if it doesn’t it doesn’t . Can’t hurt an engine much that already has a rod knocking . My drill does have a handle that screws into the side of it I can put a cheater pipe on so I don’t hurt myself .
If by chance the engine spins I’ll put a compression gauge in 1 cylinder & try it . I’m kinda leaning toward what was suggested by db4690 , just go ahead an buy the pallet engine for $500.00 if it turns ok with a breaker bar unless my drill test works .
Since I have no idea how long the pallet engine has been sitting does everyone agree that I should put a little oil in each cylinder before attempting to turn it at all ? Since it’s a V6 the cylinders will be slanted & the oil will all run to the low side . Will turning the engine distribute the oil all the way around the cylinder wall or should I try to roll the engine enough on the pallet to make the cylinders on each side vertical after I put the oil in ? So many questions ?


“put a little oil in each cylinder before attempting to turn it at all”

Yeah, do that. excellent idea

Are there any water cooled piston airplane engines still in production or even in regular use?

P51 Mustang!


Well it seems as though a starter motor cranks out a lot more hp than my drill & figuring how small that starter motor gear is & how large that flywheel gear is I think I’d better give a hat’s off to those who said it wouldn’t work . See , I’m not that hardheaded .


Now that you know . . . don’t ruin your drill


Starter motors are usually rated in KW, around one KW for an econobox engine. So that’s around 1.3 HP for a typical starter motor. But the starter motor has a mechanical advantage, turning the flywheel vs the drill turning the crankshaft bolt directly. At least we all know now whether such a thing is possible, since you’ve done the experiment.

Well , I actually haven’t tried it . I had about given up on the idea . Maybe I’ll try it yet just to put this to rest .

Starter motors are also designed to draw high current (and hence high torque) for only short periods of time. Which is why such a physically small starter has so much torque.

Running a starter continuously for a long time will cause them to overheat. I’ve seen the solder in starters melt from that.

Does Rolls Royce still produce the Merlin engine @Tester?

"Airplane cylinders are removable from an engine"

May I assume you’re talking about a radial air-cooled engine . . . ?

Same with the covair.

99% of private aviation piston engines are OHV air cooled horizontally-opposed 4 and 6 cylinders, with each cylinder separate and replaceable, like the original Beetle:

Actually the P-51 Mustang “Merlin” engines were license built by Packard.

texases: Thank you for “splainin” this saving wear and tear on my fingertips.

My 1960 MGA 1600 came with a starter crank in the tool kit. I did not use it as the starter motor powered by two 6V batteries (one behind each seat for weight distribution) worked fine. My Father whose first car was a new 1926 Ford Model T roadster ($304 FOB Denver, CO) Had a “nostalgia attack” and wanted to crank start the MG. With 8.3:1 compression ratio he started it with 3 cranks. I don’t see why the OP could not use a 1/2 inch “speed wrench” which is a hand powered crank, to at least determine if the engine with squirts of WD40 or Marvel Mystery oil has comparable compression in all cylinders. The drill would of course be less physically demanding.

OK , The verdict is in . I tried the drill today on the liberty with the rebuilt heads & knocking rod . I removed all spark plugs before trying to spin the engine . The drill turned the engine without any trouble . I installed a compression gauge in one cylinder . The engine started to turn , the compression gauge hit 50 lbs & the drill stopped turning .
I had previously done a compression test on this engine using the starter & had 150 lbs .

Interesting, thanks for reporting what you found OP.

I hand cranked a 4 cylinder Case tractor on several occasions many years ago and it was a real pain even with ether. I didn’t turn the ignition on until after spraying the ether into the intake and turing the crank several full rotations and bringing a cylinder up against compression. With the crank at about the 9:00 position against compression the ignition was turned on and the crank quickly yanked past top dead center hoping it would start. It would have been impossible to rotate the engine repeatedly to run a compression test even if only one cylinder had compression.

Until just a couple of years ago the guys at the grain elevator here used an old relic of a Case tractor that was hand cranked. I don’t know the model as all of the paint had disappeared decades ago.

They used that tractor for moving around ammonia tanks and so on. The guy that operated the tractor is about 160 pounds soaking wet and that antique always busted right off every time he cranked it.
He must be in hog heaven now with an updated tractor with an actual starter motor on it.