I have been an aircraft owner since 2010, and the single most important lesson I have learned has nothing to do with avionics, weather, or airspace. Instead it’s this: The more engaged you are in the maintenance of your airplane, the better off you and your airplane will be.
Hands-on owners know their aircraft. They track the data. They notice when something is off. Sometimes, that engagement is the only thing standing between them and a very expensive mistake. It almost happened to me.
Background: A Routine Test That Wasn’t
In the first year of owning our Cessna T310R, we put in the time and money to get the airplane the way we wanted it. It was a meaningful investment, and it paid off. After that work, the airplane has been reliable, predictable, and relatively light on surprises for several years running.
Going into 2026, I had two items on the radar: four magneto overhauls and the replacement of my 76-cubic-foot oxygen cylinder. Nothing urgent, but I knew neither would come cheap. Both were planned and manageable.
I had no idea what was coming next.
My mechanic and I had worked together for several years. It was a good relationship, solid work, agreement in maintenance philosophy … no issues. I bring squawks back after every flight and address them immediately because I don’t believe in carrying maintenance items to annual. In mid-February this year, with two weeks of known downtime on my schedule, I had my mechanic remove my four magnetos and send them out for overhaul.
During removal, my mechanic noted what he described as “excessive blow-by or air leakage” when pulling the prop through on the right engine. That led to a phone call and a request for a compression check. Given our history, I agreed immediately and nervously waited for the results.
The next day, he gave me the results: Odd cylinders on the right engine tested at 40/80, 42/80, and 40/80, while the even cylinders were in the mid-60s to low 70s over 80 with a master orifice value of 48 psi. He recommended replacing or overhauling the three “bad cylinders” at a minimum, while strongly suggesting a full top overhaul of the engine.
That information did not match the airplane I had been flying.
I had just returned from a cross-country trip, flying roughly 20 hours over the prior few weeks. The engines were happy, power was normal, oil consumption was on par, no oil on the belly, and no symptoms of anything wrong. The idea that three cylinders on one side of the engine had quickly and quietly degraded while the other three remained healthy, with zero indications, didn’t add up. We agreed to cut open the oil filter and inspect for contaminants. The results showed nothing, which made the original findings even harder to accept.
I am an avid follower of Mike Busch and Savvy Aviation. The core message being: Don’t let maintenance drive decisions that data doesn’t support. Standing in front of my airplane, something felt wrong, and it wasn’t with my engine.
Pumping the Brakes
I decided to slow everything down. Before any cylinders came off, I wanted two things: Continental Aerospace Technologies’ technical support involved and a second opinion from another mechanic. If those steps didn’t produce an answer that aligned with the data, Savvy Aviation was next. When I told my mechanic I wanted to pause, get the manufacturer involved, and bring in a second opinion, the tone changed immediately. He seemed annoyed. Phone calls went unanswered and text messages stopped being returned. When we did speak, delays were blamed on workload and other airplanes taking precedence over mine. The magneto reinstallation (a job that should have taken days) was now stretching into weeks with no clear end in sight. The airplane sat disassembled while I waited, growing increasingly frustrated and unable to schedule the second opinion until it was back together.
I considered having someone else finish the job. But our Twin Cessna requires removing several components near the magnetos just to access the attachment bolts. Walking another mechanic into a half-completed job wasn’t a good idea mechanically or professionally. I didn’t want to put mechanics against each other. So I waited.
In the meantime, I contacted Continental’s tech support with a detailed write-up including prior flights, oil consumption history, power analysis, my mechanic’s findings, plus the compression numbers. Their response came back faster than I expected. The recommendation was straightforward: perform Service Bulletin SB03-3, follow it exactly, start to finish, and report what we found.
I was already familiar with SB03-3, but having Continental point me to it directly and insist it be followed exactly as written gave me the standing to walk into the hangar and require it.
The Test Matters
Reading through SB03-3 reinforced something that is easy to overlook: The test itself matters as much as the result. Continental’s service bulletin specifies a differential pressure tester with a 0.040-inch orifice for my engines. My mechanic used a 0.060-inch tester, but that alone doesn’t explain the gap in readings. A 0.060-inch tester actually flows more air and tends to produce higher numbers than a 0.040-inch tester, not lower. The real culprits were likely technique: improperly calibrated master orifice and inadequate prop rocking to seat the rings against the cylinder wall before testing. Any one of those variables can drag readings down significantly. All of them together produced numbers that didn’t reflect the actual condition of the engine.
A proper differential compression test starts with verifying the master orifice reading before touching a single cylinder. That number tells you immediately whether the tester is calibrated correctly for your field elevation. The test itself should be performed on a hot engine, immediately after shutdown, with air pressure brought up slowly while rocking the prop to seat the rings against the cylinder wall. A rushed test on a cold engine without adequate prop rocking can and will produce readings several psi lower than the true condition of the cylinder.
My mechanic’s reported master orifice of 48 psi was a red flag. At my field elevation of 5,673 feet at KBJC, the correct master orifice should read closer to 42 psi. That gap told us something about the test before we even looked at the cylinder results.
Two months after the magnetos were removed for overhaul, they were finally reinstalled and the airplane was back together. I was then able to move on to the second opinion and follow through on the Continental tech support’s recommendations.
The Second Opinion
I went to the hangar with a second mechanic and worked through the SB line by line. We started with a fresh compression check and a full borescope of the right engine to establish a baseline. The borescope showed good crosshatching, valve seats looked clean, and nothing notable. We hooked up the correct differential compression tester, a 0.040-inch orifice tool, confirmed the master orifice at 42 psi, exactly right for the elevation, and proceeded through the full SB protocol before drawing any conclusions.
The SB calls for an in-flight test before any cylinder comes off the engine. The procedure specifies flying at 65% to 75% power long enough for oil and cylinder head temperatures to stabilize, then performing the compression check immediately after shutdown. So I decided to fly for about 45 minutes at 10,000 feet with power set to approximately 75%. When I landed and finally got the airplane back inside the hangar, it had been nearly 45 minutes since touchdown, not ideal conditions by any measure, but we proceeded to hook up the differential testing tool and still, the three problem cylinders came back at approximately 60/80.
We ran the entire SB protocol and could not duplicate my original mechanic’s findings. The engine was fine, and likely had been the entire time. That’s not a small difference from the original report. It’s the difference between major engine work and an airworthy engine.
What It Cost and What It Saved
The estimate for removing, overhauling, and reinstalling six cylinders on a TSIO-520 was between $20,000 and $25,000. That work would have started within days of the original compression check if I hadn’t stopped it, not to mention it would have been completely unnecessary.
The two months of downtime weren’t free, either. The extra labor tied to the initial blow-by finding added cost to the magneto job, and I was shocked by the amount when the bill arrived. I knew where the relationship with my original mechanic stood by that point. I paid it and moved on. Should I have argued it? Probably, but I no longer had the energy.
The magneto overhauls, along with everything else on this year’s list, including the oxygen cylinder replacement, will still make 2026 a costly one. But it won’t be the kind of year where an extra $25,000 gets piled on top of everything else.
That difference came down entirely to questioning the initial assessment instead of simply accepting it at face value.
The Lesson Learned
Stay engaged in your own maintenance. Know your engine history, track your oil consumption, turn wrenches alongside your mechanic if you’re allowed to. That engagement is what makes a report feel wrong when something doesn’t add up, and what gives you the standing to push back when it does. If I had been a hands-off owner with no data and no context, I might have signed the work order without a second thought and handed over $25,000 for work that was never needed.
Do not be afraid to stop the work, get the manufacturer involved, and demand a second opinion. Continental technical support was responsive and specific. Their guidance pointed me to SB03-3 and armed me with the data I needed to require it be followed exactly as written: correct equipment, correct technique, in-flight retest before any cylinder comes off. That procedure would have resolved this in days rather than months.
When a mechanic dismisses a manufacturer service bulletin or substitutes his own preferred tool and method, ask why. The answer will tell you something important about whether your maintenance philosophy and his are actually aligned.
The relationship with the mechanic I spent years trusting with my family’s airplane is permanently changed. A disagreement alone wouldn’t have done it, but the two months of silence and stalled work made the decision for me. Fortunately, a trusted friend pointed me toward a new shop, and we’re moving forward.
But we’re back in the air, with an airworthy engine, without a single cylinder touched. That outcome belongs entirely to one thing: staying engaged. You are the operator and owner of your aircraft. In many cases nobody understands how your airplane operates better than you do. The relationship with your mechanic matters, but so does your commitment to being involved.
A top notch and somewhat overdue article. Good work Sy.
Thank you Tom
“The relationship with the mechanic I spent years trusting with my family’s airplane is permanently changed.”
This is the single, most impactful statement about aircraft maintenance any owner can make. Certified mechanics don’t all share the same foundational understanding of aircraft or aircraft engines, and mistakes will be made. But others, including Mike Busch, have repeatedly echoed the same refrain: Cylinder compression results are not a true indicator of engine health. It is only one metric and must be evaluated as a data point among other, equally important, operational parameters.
Paul-
Thanx for your follow-up comment. And you are correct – no experienced aircraft maintenance technician should recommend and no Service Bulletin, Service Instruction, Engine Maintenance Manual, or FAA Authorized Document recommends making a decision to pull any cylinder based upon a cylinder compression test ALONE. Unfortunately, Sy Pinkert missed that point in this article.
Your comment corrects this deficiency in his article by pointing out that the compression check alone should NEVER drive any cylinder off any engine. It is merely one data point, taken together with a borescope inspection, recent engine performance data, and if necessary, a Spectometric Oil Analysis Program by someone like Blackstone Labs.
Nothing against owner/pilot involvement and assistance in performing maintenance, but please, Sy, stop promulgating the OWT’s some of us have spent years extinguishing.
John Caulkins, A&P
John, I’d welcome you to point out specifically which OWTs you feel the article promulgates. The piece advocates following the manufacturer’s published service bulletin exactly as written, verifying proper test equipment and calibration, and requiring an in-flight retest before any cylinder comes off — all of which align with sound maintenance practice. If something I wrote contradicts that, I’m genuinely open to the correction.
Great article, Sy. To be honest, an unwillingness on the part of a maintenance tech to seek a second opinion in a case like this would likely be enough for me to move on. I get nervous anytime it becomes clear someone thinks they have nothing new to learn.
Unfortunately your original mechanic was not willing to admit that he might be wrong or willing to learn something new. He also was not willing to follow clear manufacturer procedures which is a huge red flag. How dare you question his expertise? So as a response he decides to hold your aircraft hostage and teach you a lesson to never question him again. Now, a good working relationship is over, he’s lost any possible future revenue from you and you’re not likely to recommend him to anyone else you may know, so more lost revenue. He has to ask himself whether keeping that chip on his shoulder was worth it. Even after 40+ years of flying I still learn something new from time to time, often from someone younger and less experienced. I’ll let them know how helpful they were, I learned something new and they get to brag how they taught an “old guy” a new trick. Win, win for all in my book. Your original mechanic needs to grow up IMHO.
Nice article Sir!
Sy – Excellent, informative article. Many thanks!
About the last ten years of aircraft ownership, I bought a compression tester. And with it I did find how you approach the check can have a huge difference in the numbers. Slow rocking to set the rings, big difference. Our local A&P pours a small amount of MMO into the cylinder to help seal it.
I really learned from your article, Sy. Thank you. I am building my airplane and everything I can learn about operating maintenance is money in the bank. I also read/follow anything I can find by Mike Busch/Savvy.
Per Continental SB03-3, the initial indications required a flight and a re-test, assuming a satisfactory borescope inspection and lack of blow-by oil. The narrative doesn’t specify, but suggests the first leakdown was done cold, and clearly a re-test couldn’t be done with the mags removed. Here the scope inspection and re-test was performed by the new mechanic after the mags were reinstalled, and after the aircraft was flown, i.e. hot and with repositioned rings. That’s not a second opinion. It is a new set of conditions, tested with a different set of gauges.
Was a scope inspection, flight, and leakdown re-test discussed with the original mechanic?
At the annual before last on my Cessna 180K, I was informed about a low cylinder, at least 30 psi below the others. My IA discussed with me about replacing cylinders and also said that if I was going to change one, I should replace all of the cylinders on that side due to the labor involved in gaining access.
When I questioned why there was no noticeable performance degradation, he explained that, with the pressures experienced during combustion, the leak would not show itself. Then the clincher – he told me that the cylinder, though low, was within acceptable parameters and that I should just fly the airplane. “Fly the heck out of it.”
So I did. At my most recent annual the cylinder was back up to where it should have been.
The best medicine for an airplane is to fly it often and fly it right!
A well laid out and very well written article on ownership responsibilities that aren’t often discussed. Being a bit of an engineering nerd, I was able to actively participate in every annual inspection and was deeply involved in the initial pre-buy on my Funk and my Navion.
It isn’t often you can find a shop or an A/I that will let you actually participate – pull panels, pull – clean – gap plugs, change oil – including safety wiring the new filter in place, any myriad other simple tasks, but the experience is worth its weight in gold.
I wish more mechanics felt that owners should be and could be taught and trusted to do the right things, but I understand that larger shops have insurance and liability issues to worry about.
In a age where the small, ex-military mechanic/shop is disappearing I still encourage other owners to find one and develop a trust relationship with them. Sometimes you have to fly half-way across your state to find the “right” mechanic, but it is really worth it over time.
If you fly mountains, night or weather, I’d argue that an engine needs to be be opened up for inspection at 2000 hours or 20 years time in service, even if its running great.
Steve, I disagree. If the engine is happy and the data is good, then there is no good reason to split the case at an arbitrary 2000 hours or 20 years TIS. The data actually shows that infant mortality of engines is much more dangerous than an engine that is happy and well beyond TBO.
Right call. Many moons ago I recall Continental doing a test run on a 0-470 I believe in a Cessna 336/337 where field tests showed 0 or almost 0 compression on the cylinders. the engine was removed from the airframe and tested on the dynamo–resulting in full engine power delivered. Tell me I’m wrong and show me why.
Well Sy, I build all my own engines and I see a lot of interesting things when I tear them down. I also reject a lot of brand new parts. This is just my own comfort level. At least you have a twin. If my engine fails in low IFR, at night or over mountains, I am probably dead!
IMO those three cylinders are still low and will need attention sooner rather then later.