How Healthy is your Engine

[@hahahano2796]

The aviation "compression" test is an automotive leak down test. Automotive compression tests are very good indicators of engine health and can be performed hot/cold wet/dry to get a good picture of health. In automotive work leak down tests are used to try and pinpoint problem areas. Not determine health.

[@SuperYellowsubmarin]

This compression testing discussion leads me to this observation : we tend to rely more on a test that outputs a figure, no matter if the test has even more variability than a simple visual inspection.

[@darrylday30]

Thanks Mike. I’m reviewing all your webinars. Extremely useful.

[@desertdog185]

This is so brilliant!! Mike is my long time hero. Question at 16:54 for anyone with ideas: Sure, most of us can thoroughly examine oil filters, but the rest (are there cracks in the crankcase? Cracks on the cylinder heads?) I just don’t know where to look. I walk around slowly during oil changes with all the cowling removed, but I never find anything and I’m sure I don’t really know how to see problems. Yes. I’m an A&P but always learning more.

[@AwestrikeFearofGods]

1:11:50 My guess would be nickel (II) oxide, which appears to have an olive drab color. Nickel reacts with oxygen or steam at high temperatures, but excess fuel would tend to reverse this reaction (possibly removing visible indications of exhaust-valve overheating). 21:50 In automotive circles, they call this type of compression test a "leak-down test". I agree that it's a bit contrived, when it comes to realistically simulating engine performance. Would a "cranking compression test" on a warmed-up engine be more representative of actual operating conditions? Automotive mechanics use both tests. In fact, they perform the cranking compression test dry and wet (with oiled cylinder walls), because different tests reveal different leak sources (piston rings vs. intake valve, vs. exhaust valve, vs. cracked block/leaky head gasket).

[@tomasnokechtesledger1786]

Carbon and Leadsludge buildup affects the compression readings, making it unreliable. Before measuring I do an Ed wash and fly.

[@pg9511]

My airplane has 9 combustion chambers. 3 layers, 3 cylinders per layer. Is there a gauge that goes to include this odd number for CHT's and EGT's, etc. (Mazda Engine)

[@technomentis]

Thank you.

[@faainspector9699]

Roller tipped valve rockers significantly lower valve stem to valve guide wear..........the stem is not forced to one side as much with a roller tipped exhaust rocker..........

[@wntu4]

I would love to know how an engine with no compression is making power at all.

[@JosephHHHo]

In the static test at low pressure, it all vents out. Compression and combustion pressure is orders of magnitude higher with the engine spinning. It seats the compression rings more firmly, applies addition force to the valves against the seats and happens so fast there is not enough time enough gas to get past a small leak to make an overall difference. The test does not relate well to the application which is why it sucks.

[@PDZ1122]

Man, A&Ps... basically they are wrong 90% of the time in their diagnosis of anything. Doesn't surprise me though.

[@devilsoffspring5519]

Really? How would they make a living then?