Ask the A&Ps


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Experts Mike Busch, Paul New, and Colleen Sterling answer your toughest aviation maintenance questions. Submit questions to New episodes are released the first of every month.

Episode Date
"Only a CFI would ask a question like that"

This month Mike, Paul, and Colleen dive into questions about valve failures, tracking engine times, aging engine accessories, and worrying cylinder head temperatures. Plus, a question that could only come from an instructor.

Full notes below:

John is looking to avoid trouble on his aging aircraft. He asks if he should replace ancillary equipment related to the engine on his Cessna 210. Mike says we should avoid the idea of replacing equipment just because of age, and focus instead on condition. He says a turbocharger is expected to last about 1,000 hours. Rubber hoses could be an issue, as are magnetos. Paul said you can pull and replace the lifters to save the camshaft, if necessary. He also recommends inspecting the check valves on the turbocharger. A blocked valve can cause an otherwise healthy turbocharge to fail.

Ben is trying to keep track of the difference between flight time and tach time, and which to use for maintenance purposes. The hosts say the FARs are silent on this question. Always use the time that runs the slowest, they say. And you can always switch which one you track.

Ricky recently put Superior cylinders on his Cherokee and he’s worried about cylinder head temperatures going into the red on his engine monitor, which is currently set at 420 degrees. Mike said their recommendations is to limit Lycoming CHTs to 420, and the manufacturer lists the absolute maximum at 500 degrees. Even though the cylinders are from Superior the hosts make the point that they must meet the same specs as those from Lycoming, so the limitations are the same. Further, they think Ricky’s leaning procedure is to blame for the high CHTs. He typically leans to roughness, enriches it to stop the roughness, and then adds a bit more to get a 50 rpm rise. This puts the mixture in the worst possible position.

Jim is trying to separate myth from reality on engine preheating. He has an RV-7 based in New Jersey, and is wondering whether it’s ok to leave his engine preheater on at all times. Mike said that Tanis wrote a white paper saying that leaving the heater on at all times would promote rust as moisture condenses. However, adding an engine dehydrator would solve the problem. But the white paper didn’t address Jim’s specific usage, where he adds blankets and cowl plugs to bring up the temperature in the entire engine. Colleen reminds Jim that the prop is a big cold sink, so keeping it warm with a cover is essential to keeping the whole system warm.

Tom is a CFI and is curious how the green arc on the tachometer is determined. The hosts are stumped, but Mike guesses that four-cylinder engines have tachs with green arcs to about 1,000, while six-cylinder engines have tachs with a higher green area. This is because six-cylinder engines have harmonic dampeners for the crankshaft that only work in a narrow window.

Tamer calls in again after receiving some advice about a cylinder on a previous episode. Since then he’s replaced two cylinders, one that broke a valve mid-shaft. Mike said from Tamer’s description that he likely experienced a valve strike. If the valve did stick open, it’s usually because of lead deposits. He recommends reaming the exhaust valve guides to clear out the deposits. The procedure doesn’t require removing the cylinder, but it does require taking apart the valve train. A Lycoming wobble test (Service Bulletin 388 will show whether reaming is required, but Paul recommends skipping the wobble test and going straight to reaming because it doesn’t require that much more work.


Nov 01, 2021
"Compression readings are garbage"

This month Mike, Paul, and Colleen tackle everything from radio gremlins to the big questions of aviation, such as an overall maintenance philosophy and the reliability of our aircraft. 

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Detailed notes:

Phillip is trying to track down radio gremlins in his Citabria. The hosts suggest putting in a larger grounding plane, which will require some fabric work. They also say the connections to the grounding plane should be cleaned. 


Brad is wondering how reliable our engines are. Mike makes the point that complete power loss events not related to fuel issues are rare. This is because cylinder problems are the most common, and they usually don't cause a complete power loss. Colleen referenced the Nall report, which details about 10 accidents a year due to power loss events.


Gary is thinking about overhauling the engine on his Cessna turbo 210. The hosts say lower compressions aren't necessarily a reason to overhaul an engine. Indications like certain case cracks and oil analysis are more reliable markers of when it's time to overhaul. 


Mark wants to know how to manage maintenance risks on his club aircraft. The best thing someone can do is avoid maintenance unless it's necessary, he's told. Mike, Paul, and Colleen are big believers of doing maintenance on condition only. 


Ryan is wondering where the fuel is going in his 182. He used lean find on his engine monitor and got 14 gallons per hour at 9,500 feet and 2100 rpm. Mike examined the engine monitor data on the Savvy Analysis platform and found that Ryan never reached peak EGT when leaning. The hosts suggest leaning to the onset of roughness and increasing the mixture slightly until it smooths out. Colleen uses lean find, but she doesn't find it very reliable.

Oct 01, 2021
"Why can't we do something simple like clone an engine?"

This month Mike, Paul, and Colleen tackle questions big and small. A pilot wonders why aircraft engines are so expensive, a young student knows there must be a better way to clean an airplane, and owners tackle concerns over increasing compressions, throttle lag, and avionics.

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Detailed notes:

In the intro Colleen references a Lycoming service instruction on cleaning cylinders with walnut shells. Google "Lycoming Service Instruction 1418" to see it.

John asks about increasing compressions. They’ve been going up for 5 years, despite being over TBO time. The compression test is a terrible test, says Mike. Mike references a Continental graph of compression tests over 300 hours. 


Paul wonders why aircraft engines are so expensive and why we can’t just clone them to make them cheaper. Mike suggests there are three elements that create high prices on aircraft engines—the high cost of certification, low production numbers, and the high cost of liability insurance.

Abdullah asks what aircraft cleaners are effective and safe. Paul recommends Dawn dishwashing soap as a cleaner and degreaser. GoJo hand cleaner without the pumice also works well. He doesn’t recommend using a pressure washer because you are likely to wash away paint, and push particulate in between skins. Colleen and Mike both use Simple Green aircraft cleaner.

Bob’s LongEZ has engine roughness only at 2,500 rpm. Colleen references the carburetor manufacturer's website and a troubleshooting guide, found here:  Mike suggests Bob do a series of mixture sweeps at 2,500 rpm to see the data. Paul suggests that it might be a problem in the mechanical linkage.

Robert asks simply what he’s supposed to do with the split master switch. The switch enables the pilot to isolate the alternator. Although some recommend leaving the alternator off during the start to reduce load on the battery during the starting sequence, Paul, Mike, and Colleen don’t think it generally matters. Mike thinks there are only two times to consider starting with the alternator off. One is when using a depleted battery, and the other is when using ground power during the start.

Sep 01, 2021
"There's no free lunch in aviation"

Broken rocker arms, metal shards in the valve cover, and oil in the cylinder, oh my. This month Mike, Paul, and Colleen focus on listener engine problems, give some guidance on mods for an experimental builder, and bust an oversquare myth. Submit your questions to



Jeffrey had a 1964 172 with an engine miss and a stuck open exhaust valve on his number 4 cylinder. Unfortunately, the rocker arm subsequently broke. How do I keep it from happening again, he asks? Paul advised that he would want to check the wobble on the other valves. Mike reminds Jeffrey, an A&P, that you don’t have to remove a cylinder to ream the valve guides. Paul suggests reading an article on his website that explains the wobble test.  ( He said a wobble test will tell you if the valve guide has bell-mouthed or if there’s too much material that collected on the guide that cinches down on the valve, which is usually what happens.


Charlie asks whether there are downsides to flying oversquare. Mike, Paul, and Colleen recommend he check the engine operator’s manual from Lycoming, which will give detailed information on acceptable rpm and manifold combinations, including many oversquare options.


Michael has Mooney and is experimenting with a borescope. He was wondering what happens if you find oil in the cylinder, as he has in 3 of his 4 cylinders. Mike says so long as he doesn’t have spark plug fouling not to worry about it, and he relates that in his Cessna 310, whose engines are slightly canted because of the dihedral, he always finds oil in the lower engines.  Colleen said if Michael is having trouble starting the engine or if he sees lots of smoke he may need to address it.


Todd is building an RV-14 and is curious about a crankcase vacuum kit in order to have a cleaner belly and maybe gain a few horsepower. Mike, Paul, and Colleen are dubious of the claims, and Mike says he wants to know if the engine is blowing oil out the breather tube.


Nate is wondering whether overhauling his Cessna 182’s engine was a good idea. After discovering metal shards in the valve cover, he decided to go forward with an overhaul. Paul said you don’t learn much more from pulling a cylinder than you would from a borescope. Mike, Paul, and Colleen agree that significant metal in the valve cover likely came from the springs because there’s no other way for the metal to get in that area.

Aug 01, 2021
"An oil filter inspection is non-invasive, unless you're an oil filter"

A savvy owner wonders how to trust her airplane with no logbooks, a Cessna pilot is curious if he's getting all the power he paid for, and Mike, Paul, and Colleen tackle an unruly governor. Send your questions to

Jul 01, 2021
"About the half the time, reported cracked cylinders aren't cracked"

This episode Mike, Paul, and Colleen debate shock cooling, help an owner set his stall warning tab, debunk unapproved equipment myths, give an owner advice on breaking in new cylinders, and more. Submit your questions to

Jun 01, 2021
"Heavy detonation is normally a self-correcting event"

This month owners look to settle arguments with their mechanics over tire wear and avionics glitches, one pilot tries to determine myth from reality on keeping fuel tanks topped off, a pilot learns his oil pressure problem isn't a problem, and Mike, Paul, and Colleen describe why detonation is a self-correcting event. Submit your questions to

May 01, 2021
"I don't see anything that makes me want to attack the engine with tools"

This month Mike, Paul, and Colleen cover the basics of oil analysis, corrosion proofing, fuel selector play, how to pick an overhaul shop, and prop people. Send questions to

Apr 01, 2021
'If it moves, squirt it with something'

This month Mike, Paul, and Colleen tackle a number of questions about oil. Where it should be, where it shouldn't be, and why it isn't where you last added it. Plus, a jet pilot is grounded by tires. 

Mar 01, 2021
'We just saved your engine'

This month Mike, Paul, and Colleen delve into must versus should. Must you open all those inspection ports, is the prop and governor overhaul mandatory, and should one owner retorque his cylinder after a re-installation mistake? Send your questions to

Feb 01, 2021
"Did you float the dog?"

This month Mike, Colleen, and Paul revisit sticky valves, diagnose shimmy dampers, give a bit of career advice, and talk about what right looks right on throttle response. Plus, silly pilot tricks with animals! Send your questions to

Jan 01, 2021
'I went to the church of lean of peak'

Mike, Paul, and Colleen talk about why lean of peak is so beneficial. Also, the hosts tackle questions on sticky valves, how to properly break in an engine, oil consumption, and more. 

Dec 01, 2020
'You're not going to fall out of the sky because the camshaft wears'

Snake oil, cranky turbochargers, oil issues, camshaft rust, and more in this month's episode. Plus, a new owner tries to stump Mike, Paul, and Colleen on propeller rpm checks. 

Nov 01, 2020
"You're never in a situation where the IA can hold you hostage"

Corroded control cables, the right oil for engine break in, pesky fouled plugs, and just how far can you push back on your annual. Paul, Mike, and Colleen handle all these topics and more in this month's episode. 

Oct 01, 2020
I'm upside down and there's no oil in my engine!

Checking an airplane for aerobatics, engine failures due to oil starvation, mysterious airplane vibrations, and why replacing cylinders could be a bad idea. Mike, Paul, and Colleen handle these topics and more in this month's episode.

Sep 01, 2020
Introducing Ask the A&Ps

New from AOPA, it's a podcast featuring you, the pilot and aircraft owner. Experts Mike Busch, Paul New, and Colleen Sterling answer your aviation maintenance questions. Subscribe today to catch all the episodes.

Aug 10, 2020