Not only Chet but I too am a licensed aircraft mechanic ( now called in the USA "Aviation Maintenance Technician" which sounds like you should be able to keep your hands clean... but still can't.)
I worked for years for a company called Schneck Aviation, where we did complete overhauls of all the common horizontally-opposed piston engines found in light aircraft (and even the Goodyear Blimp which uses 2 counterrotating Continental engines). And I do mean complete. Total stripdowns even removing all paint, replacing all seals and gaskets, align-boring cases, turning cranks, chroming and re-honing cylinders, etc. And run-in on the Test Cell before releasing to customer. Which was my job: accept engine from buildup mechanics on the nose stand, take the engine and mount it to test cell with all temps and pressures and everything monitored, run in according to a time/RPM schedule, and most importantly, FIX any and every discrepancy noted on the test stand. Everything from leaking seals to bad magneto timing to mechanic installed wrong camshaft....
And later I worked Quality Assurance at Gary Aerospace where we did the same thing to big Radial engines, including up to PW4360 Wasp-Major.
We built firewall-forward quick engine change packages for the Israeli Air Force, EMP-hardened, for their forward air control aircraft, among other things. Then they put _me_ in charge of the Test Cells there too.
https://vimeo.com/16117810The guy with the flashlight looking for leaks... that could have been me, I even sort of look like that.
Then I worked for Mooney Aircraft at their Delivery Center here in SAT for a couple of years till they folded. That was nice, working on brand new airplanes sometimes not even painted yet, and supporting the owner pilots during their 25 hour conversion training and burn-in period at FlightSafety.
And in my spare time I overhauled VW engines for fun and profit. And just for grins, my girlfriend's 1956 titty-pink Cadillac, which dropped a valve at speed and totally destroyed most of the engine, ruined a head and bent three connecting rods. That was fun, pulling that big v-8 engine with an A-frame in her driveway, and later seeing her in overalls, all greasy, helping me to slip the pistons into the cylinders once we got the case back from the machine shop where they sleeved 3 cylinders and resurfaced the heads etc. Locating all the needed replacement parts was a trip in itself.
That's why I just laugh when someone accuses me of having dirty fingernails in a video. Wimps, they can't even use the right kitchen knife to tighten a screw on baby's pram.