KITPLANES Firewall Forward: Compression Testing

Unlock the mysteries of the aircraft-engine leakdown test, otherwise known as the differential compression test. KITPLANES engine meister Paul Dye breaks down the process of compression testing and explains what the readings mean.
This series is sponsored by Tempest Aero Group - tempestaero.com/ Visit the KITPLANES website for more tips: www.kitplanes.com/firewall-fo...
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[@eiselbay]

Im studying for my Powerplant practicals and this was a great refresher! Thank you so much!

[@lupo19047]

Paul just casually mentions "pull some spark plugs". I think it makes sense to pull a spark plug from every cylinder before beginning. That way, the engine can't kick because of a cylinder firing. It's a low, but I think non-zero, possibility. Even so, the prop can kick from the compressed air being injected. And Paul rightly cautions us about that. That's the more obvious and more likely scenario. This series is great!! Thanks Paul.

[@russlavalle]

Amazing content Paul. Whenever I see a video you're doing, I make a point to watch it!

[@helodriver20]

That was an outstanding presentation.

[@wallywally8282]

Ed’s to be done when the engine is hot👍

[@portnuefflyer]

So, it's not rocket science?! Thanks for this clear and simple explanation.

[@maheralazzawi7814]

very good

[@LTVoyager]

A brief explanation of the theory of operation of the differential tester would have been helpful.

[@KitplanesMagazine]

Ooh, good idea. We'll work on that for a short add-on video.

[@LTVoyager]

@@KitplanesMagazine It is a pretty simple concept, but I still find many who really don’t understand how the technique works.

[@user-gp2gb5zq1x]

Hi how can you maik rper can you send videy thinks

[@tedstriker754]

I've never liked doing this test. Dangerous. The prop! Best done with two persons. One to man the prop and the other to run the test and operate the air valves.

[@KitplanesMagazine]

Agreed, as long as that other person is properly briefed on the procedures. Sometimes, though, you have to do it on your own.

[@LTVoyager]

That just exposes twice as many people to danger and is a bad idea. Better to simply stay clear of the prop and expect it to swing. Then if it does, no big deal. Holding the prop beyond a low psi TDC confirmation, is extremely foolish.

[@bertsparrow]

Paul didn’t say to warm the engine up first. Thoughts?

[@KitplanesMagazine]

Warm up the engine! You can do compression testing cold but it's more representative of actual engine health when the engine is warm.

[@Rance120]

Do it cold, then if you get a low reading, you know it will only be higher if the engine it warm. Run the engine and then check pressures…they should be higher. Just another way of doing it 👍🏼 Great video!

[@normanprice2310]

You didn't mention the master orifice check which is affected by atmospheric pressure.. You are misleading the public. Borescope your engine and find out a lot more about your engines health. The only reason i conpression my 0-470 is because its required. Watch Mike Bush's videos for good info on the subject.

[@LTVoyager]

Nothing misleading here. Both procedures have value. A borescope exam is unlikely to tell you that the rings are worn out or tell you that a valve is leaking and give guidance as to which valve. The minor variations in atmospheric pressure are insignificant to this test. We are measuring to the nearest 1 psi at best, not 0.01 psi.