Ask the A&Ps podcast | Gratis online luisteren

"The engine didn't explode"
Mike, Paul, and Colleen sludge through oil pumps that lose prime, skipping an oil filter change, and using the right oil in this Texas tea-themed episode. Email [email protected] for a chance to get on the show. Join the world's largest aviation community at aopa.org Full notes below: Mike has a Cessna Bird Dog with an oil pump that isn’t cooperating. When he lets the airplane sit for a month or more, he doesn’t have oil pressure on the first start up. He’s conceived a workaround of pumping oil by hand into the engine and turning the prop backwards. Paul and Mike both describe having experienced this issue with Continentals. Mike said that Continental told him to prime the pump by removing the top spark plugs and pressurizing the case with shop air while you move the starter. Paul said they will unscrew the oil filter, fill it with oil, and then put it back on. Cameron is trying to protect the Aeronca that’s been in his family for decades. He thinks using thinner oil sounds good because its viscosity helps after not starting for a long time, but the thicker W100 might better protect? He flies mostly in the winter, but he preheats. Mike thinks his strategy to use W100 when it’s warm and multiweight is good for colder temps. Paul likes multiviscocity so he doesn’t have to worry about temperatures. Chuck is an A&P with another job, and he’s considering maintenance side hustles. He’s thinking of offering aircraft weighing services. He can either defuel aircraft or completely fill the tanks prior to going on the scales. Advisory circular 43-13 is unclear about which approach is better. Paul has always thought it strange that proper weighing procedures are in the POH, and not the service manual. That’s the first place to check, and the procedure that should be followed first. If there’s no procedure you go to the AC. He finds that most airplanes must be de-fueled first. Mike says to use FAR 43.13(a), which says that the mechanic must use the procedures in the maintenance manual, or acceptable practices and techniques. The AC has a note at the beginning saying that it’s only to be used if the manufacturer doesn’t have a process. But given that the procedure is in the POH, and not the maintenance manual, Mike suggests Chuck can pick and choose the way he weighs the airplane. Jared is looking for a more permanent oil filter solution. First he wonders if he can skip changing the filter when changing the oil, in part because they were hard to get at one point. Paul said the only time it’s required to change the filter is during annual, when the IA is required to inspect it. Mike said he would like to inspect the filter as often as possible. He considers it the most important thing to do to monitor engine condition. Although people have taken their filters beyond 100 hours, there is oil analysis data showing that it’s a bad idea. The hosts then discuss reusable oil filters. Mike changed to reusable filters prior to Oshkosh, and has been initially pleased with the results. The Challenger filter comes off, the filter element comes out of the can, and the filter then washed. He was astonished by what came out of the filter because it’s easier to see what comes out after washing versus having to see what’s in the pleats of a filter.
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1:02:12
"When they go bad the engine is toast"
Lean of peak is causing odd vibrations in a Commander, and the hosts discuss proper troubleshooting. Plus carb heat on the ground, dehydrators, and parts no longer manufactured. Email [email protected] for a chance to get on the show. Full notes below. Chip said his mechanic is concerned about lean of peak because we don’t know the actual temperature at the valve, as the temperature is taken downstream. Colleen makes the point that EGT temperatures are fine because it’s well below the valve limit temperature. Mike said valves burn only when they don’t seat properly. They shed their heat through physical contact with the seat at the cylinder head. They also shed it through the valve stem. Detonation once flying lean of peak isn’t a concern. It’s getting to that point that’s the biggest risk. Paul suggests that once you know the fuel flow at your desired power setting you can lean straight to that fuel flow and not worry about EGT or CHT until it’s set and stable. Chip is also concerned about a vibration in the floor of his Rockwell Commander. Mike suggests he do some testing to help isolate the issue. If it goes away at certain rpms, then it suggests that it’s an engine-based issue. At a constant rpm but with changing pitch, it suggests a potential airflow or airframe source. Frank is questioning the logic of the Luscombe handbook. It says to put the carb heat on for takeoff. It’s also placarded that way on the panel. The hosts can’t figure out why this would be required. The hosts suggest he ignore the handbook and operate as he would in other airplanes, in part because the engine would be breathing unfiltered air while on the ground. Bill has a Cessna 180 on floats with an O-470-50 engine. For the last few months he hasn’t been flying as much and he wants to preserve the longevity of the engine. He is looking for details on engine dehydrators and whether they actually work. Colleen looked through some research and found that those who had done some side-by-side testing had found good results. Mike said Tanis found that people who ran their heaters all the time were causing corrosion, but that if they use engine dehydrators they are fine to run the heater all the time. In other words, they seem to work. Mark is pushing back on airport naysayers that tell him autofuel is dangerous. He flies airplanes with older, small Continentals, and with all the info that has come out on the transition away from 100LL, he’s wondering if he should be worried. Mike said running on autofuel is the best thing he can do for his engine. People tell Mark he has to run at least half low lead. Mike said they’ve never seen issues with low compression engines running on autofuel. Mark flies from an airport a mile high, and locals are also telling him that vapor lock is also an issue.
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1:02:47
"It goes through cylinders like flapjacks"
Rough idle, electronic ignition basics, airplanes to avoid (or not), and the difference between detonation and pre-ignition are on tap for this episode. Email us at [email protected] for a chance to get on the show. Join the world's largest aviation community at aopa.org/join Full notes below: Stephen wants to get the engine on his Cessna 206 purring. At idle the engine stumbles down to 600 rpm. It never quits, but doesn’t run smoothly either. Mike asks if they’ve done an rpm rise test at 600 rpm. Paul explains it’s part of the installation process of a new engine. You set the engine at a set rpm, then pull the mixture back slowly to get a 25 rpm rise. More than 25 rpm means it’s running rich. Less than 25 rpm means it’s running lean. Engines don’t come out of a crate ready to go. They need to be set up properly. Mike also said that landing with full mixture rich is an issue as well. He said there are only two times you should have full mixture. One is when starting cold, and the other is when applying 100 percent power (at lower density altitudes). Mark is interested in electronic ignition for his 210, particularly the Surefly. Paul loves the Surefly on his airplane. He doesn’t love the advanced variable timing. He thinks a bit aggressive. But it is selectable, so you can turn it off if you like. Mike said he would try it with the variable timing on, and only turn it off if the CHTs are too high. Colleen said her husband has done the dual Surefly on his Legacy. He has higher CHTs, but not unacceptably high. The fuel burn is also lower, but the biggest benefit is easier starting. Erick is looking for any angle to justify buying his first love, a Cessna 337. He would prefer a turbocharged Skymaster. He’s wondering if there’s any hope for the future of these engines being affordable. You must go and buy a turbocharged Skymaster, Mike said. The engines that Mike has previously been worried about are on the pressurized Skymaster. The turbocharged engines are rated at 210 horsepower, and the pressurized ones are rated at 225 horsepower, which he thinks impacts longevity. He thinks engine longevity is related to horsepower per cubic inch. An O-470 is about .5 horsepower pre cubic inch. The TSIO-360 is around .625 horsepower per cubic inch. Warren is wondering if detonation caused a power failure in an accident he’s studied. The NTSB data shows that the cylinder reached about 700 degrees, and it went up by about 1.3 F degrees per second. Mike said CHT increases greater than 1 degree per second can only be caused by a pre-ignition event. It means that something in the cylinder was either acting like a glow plug, or if there’s a magneto failure. A cracked spark plug insulator can act like a glow plug, for example.
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1:00:25
"When it starts to talk to you it's time to replace it"
How do you know when to replace certain parts? They begin to talk to you. Find out what, why, how, and when when Mike, Paul, and Colleen tackle this and other questions. Email [email protected] for a chance to be on the show. Join the world's largest aviation community at aopa.org/join Full notes below: John is part of a club that owns a Cessna 172. Another member told him he shouldn’t move the rudder by hand when he preflights. Mike said to make sure he pushes it at a rivet line to ensure he doesn’t bend the sheet metal, but otherwise it’s ok. Paul describes how the system is built. He said in a Skyhawk the rudder pedal tension is created by springs that pull them toward the firewall. There’s not a cable tension spec. The steering bungees are between the rudder pedals and the nose gear. If you get in and push the pedals when stationary, you are putting stress on the bungees. Jarek wants to know if the FAA has lost its mind. He is wondering about the FAA’s AC 20-105, which says that engines that run past TBO have a higher rate of failure, and that engine overhauls at TBO are usually cheaper than those that are run beyond. Mike said Lycoming had previously issued a white paper that said that the typical lifespan of a crankshaft was 14,000 hours. Camshafts have corrosion issues, and don’t cause failures, and sometimes gears need to be replaced. But rarely does time impact safety. There are people inside the FAA who disagree with the policy, Mike says. On one hand they require manufacturers to set a TBO. On the other hand, they tell Part 91 operators that they can ignore it. Typically engines that fail that have run beyond TBO tend to be not related to age, but because of maintenance resulting from the fact that the engine is older. In fact, it’s usually the opposite, Mike says. Lower time engines typically fail because of infant mortality. Aaron and a partner recently purchased a Seneca with turbo Continental TSIO-360-KBs. They installed new intercoolers and the manual revision suggests new power settings. He’s ignored the chart and is flying around 30 inches lean of peak. Mike said the chart is interesting if you are operating rich of peak, but irrelevant lean of peak. The power output of the engine is determined by whichever component is in shortest supply. Rich of peak, you have more fuel than you need, so power is controlled by air through the throttle and the prop. Lean of peak, fuel is in shortest supply, so power is controlled through the mixture. He would run a slightly reduced throttle, just to avoid overworking the turbos. Rory has a Cardinal that he bought 12 years ago, and he hadn’t ever changed the ignition wires. So he started to wonder about when and why to change them. The hosts agree that if a wire fails it feels like a stumble or mis-fire because it just takes one spark plug offline. They say to run them on condition, and only change them when they start talking to you through mis-firing.
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58:27
"The people who design these airplanes don't work on them"
Metal in the filter, starting problems, and mechanics who don't understand the definition of installed are on tap this episode. Email [email protected] for a chance to be on the show. Join the world's largest aviation community at aopa.org/join Full episode notes below: Roger has a Mooney M20J that has developed an odd starting problem. Over the past few years he’s had to increase the time the boost pump runs before the engine will start, and even then it sometimes doesn’t fully catch. Paul suggested that the bellows inside the flow divider could be bad, which would cause it to perform poorly. Mike also suggested that the idle mixture could be set incorrectly as well. An rpm rise test can verify if it’s correct. Craig has a 182 that he uses to go back and forth to his fishing cabin. He took the back seat out and he wants to add in some plywood in the back to protect the structure. He isn’t planning to affix it in any way other than Velcro. His A&P told him to avoid doing this because the wood isn't burn certified. But without installing the plywood with a structural fastener, it’s not technically installed and he can carry it however he likes. Malcolm has an 182 with the Texas Skyways conversion, and it hangs up during the starting sequence. They’ve replaced the starter, bought a battery tender to check the battery, and more. It’s so obvious what the problem is, Mike says. This is a classic and common problem among Continentals. The starter drive adapter is bad, the hosts say. He can have the part repaired and it should no longer be a problem. Aaron found a significant amount of metal in the oil filter on his Piper Cherokee 140. There was aluminum in every pleat of his filter after only about 15 hours. They were thin, but large flakes. The pieces were too big to even show up in an analysis. No other metals were elevated in the analysis. Colleen suggests that it could be from the oil pump impeller, but since he only found oil in the filter, and not in the sump itself, he thinks it’s coming from the pistons. Mike said piston pins migrate back the other direction, which often means it’s self-resolving. As it turns out Aaron knew the answer. He removed all four cydlinders, and two of the piston pins were severely worn. They also found ring chatter. Mike said Superior has had issues with ring chatter and they’ve tracked down the manufacturing problem and replacing the cylinders under warranty.
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1:11:28

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 and fifteenth of every month.

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