Ask the A&Ps

Clogged injectors, how to care for an engine while training, avoiding costly altimeter checks, and engine design considerations are on tap for this episode. Email [email protected] for a chance to be on the show. Join AOPA to become a member of the world's largest aviation community at aopa.org/join Full notes below: Marko’s engine had a strong revving sound on takeoff. He saw that he had an EGT above 1,800 degrees and one that was below baseline. A run-up after landing made it seem like it one cylinder wasn’t firing. A borescope inspection revealed nothing unusual. A subsequent check of the injectors found that there was debris in one. His mechanic suggested it was a blocked injector. He’s wondering what would cause that. It turns out this event was soon after the annual when the injectors were cleaned. The hosts agree that the maintenance is clearly what caused the clogged injector. Mike said this is such a delicate operation that he thinks it’s almost as if the fuel system should only be cleaned under sterile conditions. Colleen said she used to clean hers, but now doesn’t because she knows the risks. Paul colorfully describes the problem of cross-contamination. Dylan teaches in a carbureted Seminole and he wants to treat the engines well, and is looking for best practices. He mentions shock cooling, which the hosts quickly debunk. The school’s engines are over TBO and they’ve never had to replace a cylinder. Obviously whatever the school is doing is working. He’s also wondering about failing the engines. Lycoming recommends failing the engine with mixture, but many people like to shut off the fuel. Mike said he wouldn’t worry about shutting the engine down from the fuel selector, and that it shouldn’t introduce air or other issues. Mike worked in the auto industry for many years, and he works on his own airplanes as much as possible. He’s wondering why aircraft engines don’t have ventilated crankcases. Mike said crankcase ventilation is primarily for environmental reasons. And piston aircraft engines have significantly more blowby. You don’t want to keep it in the crankcase. He said air/oil separators return a lot of junk back with the oil. You want the filth to leave as much as possible. Doug has three altimeters in his airplane, and he’s wondering how to save money on the checks. Mike thinks he shouldn’t be charged three times for three checks because you hook up the equipment once, and adding on a second or third altimeter doesn’t take too much additional time. Each check includes about five tests, according to Paul, and each has to be separately documented.

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.

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.

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.