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Ask the A&Ps

English, Leisure/Hobby/Lifestyle, 2 seasons, 57 episodes, 2 days, 3 hours, 30 minutes
Experts Mike Busch, Paul New, and Colleen Sterling answer your toughest aviation maintenance questions. Submit questions to [email protected]. New episodes are released the first of every month.
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"We call it an Italian tune-up"

Mike, Paul, and Colleen help an owner with a bad lifter that shows itself after oil changes, guide an owner through a change his maintenance schedule, discuss what constitutes damage history, and take a guess at why POH numbers change over model years. Send your questions to [email protected] for a chance to be on the show. Join the world's largest aviation community at Full notes below: Steve has a 1975 Taylorcraft with an O-200. After oil changes one of his cylinders has some valve clatter. It tends to go away sometime later, only to come back after the next change. The oil filters are always clean and the oil analysis is good. Paul said there’s not much he can do about it, and Colleen said it’s also not a big safety of flight issue. Mike suggests they measure the dry tappet clearance to see if it’s wide enough to accommodate a larger pushrod to help eliminate the problem. Colleen said she read about a technique to fly it full power for an hour to see if resolves. They call it an Italian tune-up. Jim is on board with condition-based maintenance, and wants to alter the rubber hose component change schedule in his Rotax. Mike suggests that Jim can extend the change interval to maybe 10 years because he lives in the Midwest, and keeps his airplane hangered. The hosts discuss their method for inspecting hoses, how to manufacture them, and the various materials and considerations. Ken is considering a Cessna 180 with damage history. It was repaired and has flown 200 hours since repair. The damage history in question wasn’t so much damage as an improperly installed part that was replaced. Metal was found in the filter, a top overhaul was completed, and the owner is confident the airplane is running well now. Mike said the two things he needs to consider are whether the cylinders were reworked appropriately, and whether they were installed correctly. Considering it was a reputable overhaul company, the hosts are confident everything is ok to move forward. Scott wonders why on the same airframe, the performance speeds change over time. Paul guesses that early performance numbers were a combination of optimism, marketing, and guessing. And newer numbers are spot-on and well tested. Mike guesses that aircraft generally get heavier over time and maximum gross weights increase, necessitating speed increases.
12/15/202356 minutes, 25 seconds
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Live from Airventure 2023

Live from EAA Airventure 2023, check out our second in-person show. The questions come fast, and everything from proper leaning to oil leaks is covered. Can Oshkosh-goers stump Mike, Paul, and Colleen? Full notes below: The first question has Colleen in stitches. Can you widen the gap on your spark plugs to get more horsepower from an engine? Short answer? No! Don’t do it, the hosts agree. Even Colleen, who races airplanes at Reno, says she’s never heard of doing this. Richard has a 182 and says the book will allow for high rpm and low manifold pressure, or low rpm and high manifold pressure for a given percent power setting. He wants to know which is better for the engine. The hosts say that rpm puts strain on the engine, so they would choose high manifold pressure and low rpm. The idea of “oversquare” is a relic and not at all true, they say. Julie has a 1979 Grumman Tiger and she wants the hosts to address owner-produced parts. Owner-produced parts must be made to the original spec from the manufacturer, which can be hard to track down. But, assuming the owner can find the spec, he or she must be involved in the manufacturing process. Ultimately it’s up to the mechanic to decide whether or not to install the part, and therefore take on all the liability. Bottom line is work with the mechanic early to get his or her blessing. Vedant asks how many more hours he can operate the 2,900-hour engine in his Bonanza. His engine has good compressions and only burns a quart every 20 hours. Colleen said conditioning monitoring is all about catching early indications of problems. Mike said there are only two compelling reasons to overhaul an engine. One is that you have solid evidence that there is something wrong in the bottom end that can’t be rectified without splitting the case. The other reason is that you can’t sleep at night. Terry has a 182 with an O-470 and can’t keep cylinder 1 below 400 degrees, even at altitude. That’s the right rear cylinder with a vertical baffle right behind it. He checked that. When it’s one cylinder Colleen said it’s usually airflow. Paul suggested a GAMI lean test and an induction leak test as well, just to be sure. Rex has a 182 and wonders about flying in the smoke that’s been prevalent around the country this year. The consensus is that smoke won’t hurt the engine, but changing the oil and induction air filter more often are good ideas. Tim wants to know about leaning his Mooney M20C. He wonders whether he should lean until it’s pretty smooth or really smooth. Mike said you have to accept a small amount of additional roughness if you want to run really lean. David has a 1979 172N and he’s wondering if he can use Camguard with his Lycoming 0-320-H2AD. Mike said he should use the AD-compliant additive just to remain legal. Greg asks for downsides to using variable-timed electronic ignitions in a carbureted engines. Paul said the risk is if they advance too far you can get into detonation. He recommends checking the cylinder head temperatures to make sure they aren’t too high. Advanced timing will show high CHTs and low EGTs, and retarded timing is the opposite. Jack has a Piper J-3 Cub with a Continental C-85 with only 40 hours. After flying he finds oil all over the belly but no obvious leaks. Paul said if the breather line is cut at the wrong angle it can actually cause a vacuum and draw oil out of the case. Mike said to borescope the cylinders with the intake valve open. It should be dry. If it’s wet you know where the oil is coming from. Mike asks about rpm on the ground and lead scavenging. The hosts say to lean as far as you can, regardless of rpm. Mike said not leaning on the ground is the biggest cause of valve sticking. Paul mentioned that Cessna now recommends leaning while at 1800 during the run-up and he said you can use that setting for ground leaning.
8/15/202349 minutes, 15 seconds
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"This is a classic infant mortality failure"

With two important airworthiness directives recently issued for Continental engines and Cessna Cardinals and 210s, Mike, Paul, and Colleen dig deep on the surrounding capacity and safety issues. Then they take calls on the limitations of engine monitors, and how normal can look anything but. Submit your questions to [email protected] for a chance to get on the show. Full notes below: Michael has a turbonormalized Bonanza and he’s concerned his system isn’t operating properly. When full throttle on takeoff it overboosts, so he goes to partial throttle, which lowers the fuel flow. The controller and waste gate were both checked with no change. Mike says it’s a very bad idea to limit the manifold pressure with throttle. Continental says overboosting by 3 inches is a non-event. What is a big event is limiting fuel flow. The fuel flow is determined by the upper deck pressure, which could be adjusted. Either way, Mike says that Michael can leave it alone and give it all the beans. Paul is shopping for an engine monitor and is wondering if the hosts have any advice. Of course they do! Mike recommends user-programmable alerts. Otherwise they recommend you buy the one that best fits in your panel. A slew of recommendations on how to use it follow. Laurie’s engine runs roughly in a certain rpm range unless she leans to peak EGT. The hosts soon learn that she operates from an airport at more than 7,000 feet. Mike thinks it’s likely this is normal behavior because the engine runs too rich at full power at such a high elevation. John thinks he might be experiencing morning sickness on his RV-7’s O-360 engine. He is noticing an increase of lead buildup each time he borescopes it. The CHTs are also too low, at around 300 degrees in the winter. He felt the engine was running rough for a few minutes after starting, as well. The hosts look at John’s photos and think his engine is perfect. Paul mentions that so long as the valve seats well, the gunk in the cylinder is fine. They offer a number of ideas on increasing his CHTs. Steve is frustrated with his engine monitor because he's experiencing what he believes are nuisance alarms. The issue is that his engine manual and POH have different numbers, and the engine monitor is programmed with the POH numbers. The engine monitor can be reprogrammed, but it’s expensive and requires input from a mechanic. This is mostly an issue with engine monitors that are certificated for primary replacement.
4/1/20231 hour, 12 minutes, 9 seconds
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"You have two options and a top overhaul isn't one of them"

Adam flies a Piper Warrior owned by his friend. On a recent flight he experienced some morning sickness that he was able to resolve. On a subsequent flight the owner had morning sickness as well. The owner is considering a top overhaul. Mike said he has two options, and a top overhaul isn’t one of them. The first is to do a wobble test and the second is to skip the test and go straight to reaming the valve guides. Paul recommends doing only one at a time. He said not to fly it again until the procedure is completed. They’re worried that flying it after the morning sickness could have caused damaged, so a borescope inspection is in order as well. AOPA r Kevin flies a Cessna 172XP that he suspects is the slowest one of its kind. It flies about 15 knots slower than book speed, and he’s seeking a remedy. Paul suggests first checking the rigging, specifically to make sure the flaps are completely retracting. If the flap rollers touch the end of the slots before the switch turns off, it will hurt the motor. But if there’s a gap after the motor has stopped, they aren’t full up. Totally ignore the fairing that’s riveted to the cabin, he said. He would also check the lifters to ensure complete motion. Mike suggests that is the airplane climbs at book values, he has a drag problem, but if it climbs worse than book, it’s a power problem. Greg is hoping to overcome the supply chain issues by purchasing a “lifetime” oil filter. Being able to open the filter is the best thing you can do to know how the engine is wearing, Paul thinks. Mike thinks the filter inspection, while possible with a reusable filter, would be a messy, complicated job. Ken said he heard an adage that you should check your EGTs at 1,000 feet, and then lean in the climb to match those numbers, and he’s wondering about its validity. The hosts all completely agree, and it’s generally how they fly as well. Patrick flies a Cessna 170 and he’s wondering why his cylinders have a different CHT limit. Mike thinks the difference is probably due to the fact that CHTs are measured in a different position in his engine than others and the O-300 has a different cylinder design. After a cylinder swap he’s also wondering why break-in procedures sometimes call for changing power settings. Mike said he’s never seen a justification for this practice. He has broken in his engines by running them as hard as he could, keeping in mind cylinder temperature limits. Miko maintains his own airplanes and is looking for approved data. He’s struggling to find reasonably priced maintenance manuals. Clearly the manufacturer is the first place to go. Paul uses ATP for his airworthiness directive research. Typically they sell subscriptions, which are quite expensive though. He said you might be able to get a shop to give you their old paper manual because most have transitioned to digital. Colleen also uses McCurtain, which they don’t think exists any longer. Essco is still around and sells digital versions of scanned manuals.
12/1/20221 hour, 3 minutes, 10 seconds
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"We're card-carrying members of overthinkers anonymous"

Making new parts, protecting parts, replacing parts, and identifying bad parts is the theme of this month's episode. Plus, a spirited discussion on fuel selectors. Send your questions to [email protected] for a chance to be on the show. Full details below: Greg is building an RV-10, and he’s wondering if he should prime all the skins while he builds to ensure there’s good protection inside and out. Mike, Paul, and Colleen disagree on what to do. Paul thinks he should skip the priming and instead spray Boeshield or AV-8 because you can spray it on after the airplane is built. It’s a one-time application. Mike thinks if Cessnas have lasted for decades without being primed, Greg should be ok as well. And Colleen is on the fence. Bottom line: there’s no right answer, just the right answer for each builder. Russ is trying to help a friend. His 182R lower door hinge is cracked and the mechanic isn’t any help. Russ owns a machine shop and thinks he can manufacture the part. Mike says that it is important not to create a part that is better than the original. He must create an equal part. Something better would require additional approvals. Paul says it’s important to get the mechanic involved early because he will assume the greatest liability, and must be comfortable installing the owner-produced part. And many mechanics aren’t comfortable installing something without a part number. All agree that the hardest part of making the part will be figuring out exactly what the original material is and how it was made. Frank wants to use a synthetic oil in his 182 because he’s had such good results in his car. Mike makes the point that there’s no full synthetic oil on the market. He suggests 15w50, a semi-synthetic, but only because Frank is able to regularly run mogas. Those who only run with 100LL shouldn’t use a semi-synthetic, Mike said. Ryan is part of a flying club and they have a Cherokee 140 with an intermittent landing light. He was able to get the light to work regularly by applying a bit of heat to the circuit breaker, which makes him think the breaker is bad. The hosts recommended buying his own breaker and asking the mechanic to replace it. It’s a relatively easy fix. They recommend going to a pull breaker instead. Ernest said his mechanic hears a knock, but the hosts all agree that the video clearly sounds like lifter clatter. Mike say to look left, look right, make sure no one is around and pour in some Marvel Mystery Oil, which can reduce lifter clatter. When the lifter doesn’t fully lift there is play in the valve train, which makes the noise. Cleaning the lifter is an option, but it is a lot of work. Paul thinks it’s possible it only happens at lower oil pressures. With normal oil temperatures he should have 80 psi oil pressure at cruise, and not something lower, like 65. Alex sparked a spirited discussion on pilot technique. He’s wondering about how to test fuel flow on the ground. Some airplanes call for changing tanks on the ground, others don’t. Colleen thinks it’s ill-advised to switch tanks during the run-up. Paul said the fuel bowl on many carbureted engines contain about 30 seconds of fuel at cruise power. He said you’ll never run the engine long enough on the second tank to properly test it. This led to a long discussion about Cessna’s fuel selector design. Mike said he never moved the fuel selector off of Both in his 182, and furthermore he doesn’t understand why Cessna even made it. While the Cardinal will drain from the selected tank, the 182 doesn’t work the same way. If you burn off the right tank, for example, the fuel will be replaced with fuel from the left tank, and not air. Paul said he would stay on Both if he could. They then debate whether to use the fuel pump when switching tanks, and for many reasons Paul recommends sticking to the POH.
10/1/202257 minutes, 19 seconds