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

A Vans customer wonders what to do next, and a 172 pilot asks if carb heat is really necessary all the way to the ground. Plus, the best spark plugs, and a vexing gear issue are on tap for Mike, Paul, and Collen this time. Email podcasts@aopa.org to be on the show.

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Full notes below:
Greg has a kit from Vans on order and he’s wondering what to do next. He can replace his quick build wing kit with the small cracks installed, but he wants to know if he should order replacements. Paul said when sheet metal work is done on certified aircraft in the field, a lot of cracks naturally come up. Greg said a customer has to agree to accept the modified terms of the new contract, and you have to either accept what they send you, or spend money on a second kit. Paul said to deburr as little as possible. The goal is clean, sharp corners, not a knife edge that can cut the rivet. Just barely touch the hole, he said.

Travis has an unusual gear problem. He was tasked with ferrying a Wheeler Express RG, an unusual experimental. On the ground the gear works perfectly, but when flying it won’t reliably retract. The system is based on a Glasair 3, and Colleen said the Glasair racers have a similar experience with their airplanes at Reno. On a ferry flight the hydraulic fluid built pressure over a few hours, and Travis had to select the gear down lever in order to release the pressure. Paul said not to spend any more time on the system, and replace it with something from Cessna.

Brian wants to get to the bottom of the fine wire and massive plug choice. His shop said he had to replace all 12 fine wire plugs at the last annual, all with around 800 hours on them. The shop recommended Temptest massives, which is what he did. He’s wondering if there’s really a difference in performance. Paul said fine wires tend to idle a little better and smoother. Corrosion was an issue on older Champion fine wires, which is what Brian had. And the ceramic is thicker on Tempest. Fine wires also last longer, usually long enough to cover the additional cost. Mike said they cost about four times as much, but last four times as long. He said some people also report smoother operation at very lean mixtures and small fuel economy improvements. Colleen has fine wire Tempests in her Cardinal but massives in her Skybolt. Her fine wires run a bit cleaner and don’t need to be gapped. Brian has seen a larger EGT differential when flying lean of peak with the massives.

Dennis has a 172 and he wants to know if it’s really necessary to keep carb heat on all the way to the ground. Mike said a newer Lycoming Skyhawk is less susceptible to carb ice, but his Continental O-300 is much more likely to produce ice. He recommends installing a carb heat gauge if he really wants to avoid having the carb heat on longer than necessary.

Ask the A&Ps

This guy is on his own, he's a test pilot

This episode Mike, Paul, and Colleen help an owner with an engine that randomly dies after 2100 rpm. Plus, the role of avgas as a lubricant, prop governor issues, and getting back into maintenance. Email your question to podcasts@aopa.org for a chance to be on the show.

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Full notes below:
Dennis has a Cardinal RG with a prop governor issue. When it’s warm, the prop underspeeds just a little. He’s done a bunch of troubleshooting, and he is at a loss. The manufacturer said to send his prop in, but he is reluctant to do that given how often prop shops deem them unfit for continued service. Dennis is an A&P and he asks if he is allowed to open up the governor and work on it. Mike said he doesn’t advise it because he both can’t do it legally and doesn’t have the right tools. Both Paul and Colleen said their props do the same thing, and they recommend he crank up the rpm just a little since a small amount of overspeed is allowed under the type design.

Luis is looking to get back into aviation maintenance after earning an A&P many years ago. The hosts debate the FAR, which says that a mechanic is current if the Administrator deems he or she so, or if the mechanic has served as a technician for the past six months. The hosts think Luis should use the preventative maintenance provisions to do the work without supervision.

Jeff built an airplane with a PZL Franklin 235 and the engine won’t make full power. The static rpm is 2800, and anything beyond 2100 kills the engine. He thinks either his homemade exhaust is causing too much back pressure, or there was a manufacturing issue. He wonders if there’s a way to isolate the problem. The ignition timing is set to 32 degrees, which is the manufacturer spec. Mike and Paul recommend backing off the timing first to see what happens. Paul suggests he could also remove part of the exhaust to see what happens.

Josh wonders if we are too eager to get off avgas, specifically because of its proprieties as a lubricant. He’s always heard that it lubricates valves, but Mike thinks it’s probably not a concern. It’s true that before valve seats were hardened, there was some microwelding, which led to valve seat recession. Lycoming switched to hardened valve seats in the 90s, and Continental switched in the early 2000s. There is a possibility that some of the older Continental cylinders could have problems with valve recession, but it's too early to tell. He details the work that AOPA is doing with the dual-fuel Baron, which is seeking to understand some of these issues.

Let us know how the exorcism goes

Mike, Paul, and Colleen help an owner raise his oil temperatures, explain the rules around ELT battery replacements, debate the merits of a tuned exhaust, and help an owner whose airplane won't quit. Email podcasts@aopa.org for your chance to get on the show.
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Full notes below:
Chris has a Super Decathlon with CHTs as low as 270 degrees and oil temperature around 150. Even with the oil cooler covered during winter, it still doesn’t get hot enough. Mike said they like to see oil temperature up to 200 degrees if possible. Chris can check the vernitherm by putting it in boiling water to see when it actuates. Mike said the oil temperature gauge is typically reading at the coolest part of the process, and the oil may climb 40 degrees higher. 

Curtis just wanted to change his ELT battery. His mechanic sent it away to a service center. He received an invoice with three options, none of which included replacing the battery. His standby current apparently tested high. Unfortunately Curtis was in an unusual situation with a foreign-produced part. There are two answers, Mike said. There’s the answer where you feel like you have to follow the manual, and one if you follow the regulations. The manual says the battery must be replaced by a Part 145 shop, but the regs allow the owner to do it under preventative maintenance. Mike contends that since the battery replacement section of the manual is not an airworthiness limitation, Curtis can just brush it off. 

Pierre-Louis and his club in Switzerland have a tuned exhaust system on their airplane and while he is seeing some benefits in terms of fuel burn and climb rate, he is most interested in the smoothness of the engine. He said it feels like having a 6-cylinder engine and he’s wondering if tuned exhaust systems offer better engine longevity. Colleen thinks it’s possible the engine is actually working harder (more horsepower), so she guesses that the engine longevity would be reduced. Mike said he disagrees because the engine isn't producing more power, its power is being used more efficiently. Paul suggests that less vibration is ultimately better for the engine. 

Frank has a Rockwell Commander 112 and when he shuts it down it sometimes diesels, or won’t entirely quit. Typically it only happens in the summer after a flight when it’s warm. Mike and Paul said the only way that happens is if the mixture doesn’t fully shut off the fuel supply. Mike said the mixture cable to the carb is the first place to check. Colleen suggests that it could be a leaking primer as well. Mike recommends fault isolating it by disconnecting the primer to see if it resolves.

The breather is a slobber pot

This episode Mike, Paul, and Colleen debunk myths, describe valves that are eligible for lapping, and cover the basics of the red box and leaning. Email podcasts@aopa.org for a chance to get on the show.

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Full notes below:
Maciej is a new private pilot who is questioning some operational procedures he was taught. He was taught not to put fuel back into the tanks after sumping it, and he thinks if you sample it and it’s clean, why not put it back? The hosts agree that if the sample is clean, put it back. He also wonders about oversquare on the impact on the propeller. A ground school he took says that it is too hard on the propeller to run it at low rpm and high power. Mike questions the validity of this, and Paul said to go ask the source because it doesn't seem right to him either.
George has an airplane with some valve issues. Five of his cylinders have varying levels of green on them. He was told that four could probably be lapped, but the fifth has to be pulled. He’s wondering if green on a valve, which is later lapped clean, weakens or otherwise compromises the valve. Most of the green you see is green deposits, according to Mike. In early days of borescoping cylinders, the colors on the face of the valve were all we had to go on. Now, when we can position the camera between the valve and the seat, and can see if there’s erosion. If there isn’t erosion, it’s a good candidate for lapping. Mike said as long as the valve isn’t a train wreck that it’s worth lapping. Most people don’t do it aggressively enough.
Doug is an instructor who was flying a Cessna 182 with a client and the owner didn’t want him to lean, even though they were flying higher than 8,000 feet. Finally he convinced the owner that it was ok to lean a little to smooth out the engine. Apparently the owner was worried about the red box. Since the goal is to stay below 400 degrees on the cylinder head temperatures, Mike thinks it’s hard to get 182 cylinders that hot at altitude, and below 400 degrees there is no red box. Paul makes the point that because power output at 8,000 feet is below 65 percent, you can’t hurt the engine by leaning.

AOPA

Ask the A&Ps by AOPA

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