Unbelievable Compressions

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The FARs require a differential compression test to be performed at every annual inspection, but it's a really terrible test that is neither reliable (i.e., repeatable) nor a valid indiction of cylinder health. In this webinar, Mike Busch A&P/IA demonstrates its shortcomings, explains its pitfalls, and emphasizes whay poor compression alone should never justify cylinder removal unless backed up by more trustworthy supporting evidence such as a borescope inspection. Savvy Aviation offers Professional Maintenance Services to owners of General Aviation aircraft, such as: SavvyMx (Professional Maintenance Management), SavvyQA (Expert Consulting), SavvyPrebuy, SavvyAnalysis (Engine Data Analysis) and Breakdown Assistance. Savvy also publishes a monthly newsletter with lots of interesting information for the general aviation enthusiast; subscribe to it at www.savvyaviation.com or text the word "Savvy" to 33777. This webinar was hosted by the Experimental Aircraft Association (EAA).

Опубликовано:

15 авг 2023

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Комментарии : 43

@alanluster950

I just got your book "Engines", and have listened to 75% of your video catalog, so far. I now feel over confident in preparation for my upcoming O&P's for my Powerplant certificate. Paying $30 for your book is nothing, considering all of the free quality information you have given in your podcasts.

@youngskyculler

I love that comment about tearing down a compression tester to find "a tiny pair of dice". Brilliant. Love your content. I wish you had like-minded guest speakers (or yourself) with significant Rotax experience. Keep up the good content.

@s35bonanzapilot84

Mike, the TCM Service Bulletin you referred to pertaining to opposite direction rotation to check a cylinder with low compression is M84-15.

@dmitrydk4861

Thanks a lot for another great webinar! It was great to attend the „live version“ of the „Ask the A&P“ podcast in Oshkosh!

@gclaytony

The VA-400 would be the borescope most would want to use and is available for $250 (I purchased mine years ago so don't have the updated camera). The VA-450 you mentioned is an $800 piece of kit that includes a dedicated display. A shop might consider the additional cost/dedicated display worth the expense, but I don't believe most owners would.

@petepeterson5337

Excellent information as always. I am personally aware of a badly flunked compression (leak-down) test on almost all cylinders, where the compression tester was at fault. Grabbing another one and it indicated similar fails, and IT was faulty. The clue was when hand turning the prop, the compression seemed to REALLY hold. I have seen engines with low compression where hand turning the prop shows a fairly rapid release of cylinder pressure against the prop. A NEW correct compression tester (drove out to Spruce) gave believable answers.

@tomasnokechtesledger1786

Lots of relevant legal based info, killing the confusion. Great content asvusual, Mike!

@jukkaovaska1175

Very informative, we never stop learning

@dlain200

Great great content, one of the best on youtube, i would like to also see some info on turboprops, i will be in charge of a king air now and would love to know all about the maintenance and how to fly it to the thread, your videos have helped me a lot with my 182 and just with knowledge in general so thank you so much.

@billbrasher3437

Near and dear to my heart too. Brought many cylinders back with a quick simple in-place lapping. Doesn’t make a mess. 20’s to 70’s. Clean with swabs soaked in AeroKroil.

@spikekavalench

Excellent!

@GamingwithGamerGirls

None of the shops I've worked in have ever done hot or even warm compression tests

@tonyc223

Retired auto tech here. Compression readings are used to find a problem only if you are diag.a problem.

@johnschreiber1574

The differential compression test has huge usefulness, in that you can hear where compression is being lost. A dynamic compression test can't do this. You will still need to do a leak down (differential pressure) test to diagnose the problem.

@josephkaminski1857

I agree with this, with one exception Mike. If you rely on manufacture SB to evaluate compression testing numbers for airworthiness, then you have to also rely on them for TBO, numbers. They all limit the motors to TBO of 2k Hrs run time. In other words, even a good Compression test on a motor over TBO is not recommended according to manufacturer. You can't pick Manufacture for specs on compression evaluation, and pick AC 43-13-1b for TBO , which says as long as compression is ok, your good. that's mixing apples and oranges and calling them the same. The manufacturer specs presume if you are following them on compression evaluation, you are also following them on TBO time.

@Flaviorrodolfo

When you mentioned about "crocked piston", I'm thinking about the common piston slap on Continentals (commonly on the small ones like the O-200), would really like a video about this...

@user-kq6xf4om3l

This is the crap that ends up driving the average person out of aviation. Cold/improper compression checks=$$$$$

@paulschannel3046

Could you do a short video on how to use the master orfice tool? Is it used on just cont. or lycomings too?? I have your engine book and the manifesto as well. Love them and refer to the engine quite often. Thank you.

@GalenCop9

How do "gapless" rings affect this dynamic of unreliable compression testing and anomalies associated with the compression test?

@3SM20Pilot

I missed this presentation at Oshkosh, I went to most of the others though. Since returning from Osh I did an owner assisted annual on my plane. All of the cylinders were a good 10PSI lower than they normally are with one right at 60. The IA signed off but is requiring a retest after flying. This is the first year that I've done an owner assisted annual and thought it was strange we weren't heating up the engine first. I'm going to fly it to the Mooney service center near by and have them retest it and give me a quote to fix the squawks that were found.