Ask the A&Ps

Carbon monoxide, kickbacks, avionics upgrades, and leaning radials are on tap. Email podcasts@aopa.org for a chance to be on the show.

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Bill has a Cessna 210 and in climb he gets 50-100 ppm on his CO gauge. When he levels and goes lean of peak it goes back to normal. He's also noticed that if he puts the heat on he also doesn't have a high reading on his gauge. It's not from a hole in the firewall, Paul says. The most common places it can come in are from the header tanks where they come in through the belly, the steering boots on the nose gear, the down-lock boots on the main gear down-locks, the pilot's cabin door (look for light in the lower left corner of the door for light while in flight). The level goes down when he turns on the heat because he's pressurizing the cabin, which keeps the CO draft out. And he doesn't get it at LOP because he doesn't have nearly as much un-combusted fuel in this state, the driver of CO.

Bob has a Cessna 182 and it has a North Point (nee P-Ponk) engine with an MT prop and experienced a kickback during start. He's wondering how to move forward. His mechanic recommended removing one of the impulse couplings (he has two). The kickback would occur if one of them didn't activate properly, Paul said. If the ignition fires early during the start process, the impulse coupling delays the spark until top dead center. If it fails, it doesn't delay it, and the kickback occurs. When the kickback happens, the nylon gears in the mags are stressed, the spring in the starter adapter can break. The hosts recommend changing that and inspecting the impulse coupling. The hosts gristle when Bob mentioned the MT prop. It's so much lighter than aluminum, and they result in many more kickbacks.

Kyle is wondering about the leaning philosophy on the R-985 engine on the Beaver he flies. The manual cautions against leaning below 5,000 feet, and he's wondering what the hosts think. Colleen said since it's his employer's airplane and there's no engine monitor in the Beaver to just keep it full rich as directed. Mike said he might fly it in cruise just like a typical 4-cylinder and lean to the onset of roughness and enrichen it only until smooth again.

Erick is looking at purchasing a Columbia 400 with legacy avionics and he's thinking ahead to potential long-term maintenance issues. The hosts explain the potential repair, maintenance, and replacement options. These include the Avidyne yearly maintenance fee he can choose to do with Avidyne, or he could install Garmin, which is STC'd. The MFD has an AD to replace the battery after 10 years.

Worn intake valves, pitted camshafts, shock cooling, and AD compliance are on the docket.

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Norm wonders whether condition-based maintenance and inspections failed him. He is co-owners in an airplane with a Lycoming IO-360, and after a few years they found a crack in the crankcase. The engine was torn down and found to have some rust on the cylinder walls, scoring on the crankshaft, and a worn and pitted lifter. They had been borescoping, doing oil analysis, looking at the filter, and never found any concerns. The hosts say the approach worked perfectly. The point of condition-based maintenance is to fix safety related problems, and they argue that all Norm's issues were financial issues. Mike argues that the lifter wear could have been found with by measuring the valve opening, but that it wouldn't have necessarily resulted in a teardown. The oil analysis wouldn't have found anything because the metal chunks were too large, and although a magnet over the filter material may have helped, he's not sure that would have resulted in a teardown either. The lesson is that the airplane was safe, despite the condition concerns.

Jay has an RV with an experimental IO-540 that he loves. A look at the cylinder data found that one of his intake valves was eroding. As the shop dug into the engine they found a few other issues, including pitting on the camshaft. An IRAN is going to cost him maybe $20,000 or $30,000 less than an overhaul, so he's wondering if it's ok to save the money or should he just overhaul the engine while it's off. The hosts tell him to save his money. The only reason they would overhaul now is to increase the market value if he were planning on selling. Otherwise there's little benefit.

Ronan wonders how to interpret the data on his friend's Piper Arrow as regards shock cooling. They often get the alerts on the Garmin engine analyzer, and they are wondering if there's anything they can do to avoid it. Paul jokes that he should just turn that feature off. Mike said the only time you have to worry about this is when the cylinders are at high temperature, such as cruise to chopping the power. But in a descent the cylinders are already cooling, so he's not worried about it.

Bill is wondering if his club is documenting too much on AD compliance. The hosts give some detailed information on how they document ADs and why it matters. They tend to document everything in a large spreadsheet and note whether or not it applies. If it doesn't, they say so on the document and leave it for a future mechanic or owner. Doing so helps with hours of research, they say. They are also careful to document parts and accessories, especially those inside the engine, as you don't want to have to take the prop off to check a crankshaft serial number every year, for example.

Rising temperatures, unnecessary overhauls, unusual rigging, and ancient cloth in the wheel well are featured. Email podcasts@aopa.org for a chance to get on the show.

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Sticky valves, sleepy valves, and valves destined for the trash are on tap this episode. Email podcasts@aopa.org for a chance to get on the show.

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Full episode notes below:

Mac is trying to get a cylinder to wake up on his Piper Lance. The engine ran rough, and a magneto clearing procedure didn't help. The number 5 cylinder was dropping off according to the engine monitor. It's also next to the turbocharging exhaust. His A&P thought maybe the injector line being next to the pipe might be causing a problem. It only happens after landing, not while flying. Paul thinks it would be a more widespread issue if the plumbing engineering were the issue. The aux fuel pump stops it from happening. Mike suggests a mixture that's too lean could cause this. They suggest checking the idle mixture rise on shutdown. The rpm should rise 25-50 when pulling the mixture at idle. If it doesn't rise as much it's too lean, and if it rises too much it's too rich. They also suggest running a GAMI lean test to determine if the cylinder is a lean outlier.

Conor has a Cessna 150. On the way back from Oshkosh last year he experienced a stuck valve. There was discoloration from being hot when the cylinder was pulled. He leans aggressively. He's wondering if he's leaning too aggressively and is getting the engine too hot. He leans to roughness and enrichens only until it gets smooth. The hosts think the engine has to be in detonation for it to get too hot. The piston tops are fine under borescope, so the hosts think it's fine.

Andrew wants to knock the rust off his A&P certificate. The hosts suggest the new Savvy Aviation IA recurrent course. It's a free 8-hour course to help refresh his memory. Beyond that, Paul suggests a 172 course, which is the airplane he plans on buying. There really isn't a hands-on refresher course, according to Colleen. She suggests he could hire an A&P and work alongside him or her to brush up. He could also take an LSA repairman course, which is shorter than a typical A&P course.

James is asking about the right time to overhaul an engine. He is in a club with a Diamond that flies about 500 hours a year. When he wrote in there were 1,900 hours on the engine. They were told the turnaround would be three months. They decided to order a reman from Lycoming, which was scheduled to take 15 months. Then they got a notice that it would be an additional 12 months. It ended up only being 17 months. Their club decided that more than three months of downtime wasn't acceptable. If the lead time for engines is more than a year, so how do you listen to the engine when the delay is so long. Paul said you buy consumables, like cylinders. Cylinders can sit on the shelf for a long time.

Avoiding maintenance can be a good thing when what's recommended is unnecessary.

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Dominick is questioning his mechanic's advice on prop overhauls. He has a Cessna 310 and his left rpm is too low on approach when the control is full forward. It's not an issue on the ground or on takeoff. His mechanic recommends overhauling the propeller, and since he's doing one he should do both. He swapped governors and that didn't change anything. He sent the prop back for IRAN and they didn't find anything significant. Paul suggests it's the low pitch stops. This is a classic twin owner trap, Mike says. The two engines are never the same. Everyone agrees that he can leave it as is. 

Vas has an RV-10 and the Lycoming IO-540 has been acting up. During some flight training in the airplane, he noticed oil consumption went up, metal was in the filter, and he ended up overhauling the engine. He's wondering if he should have just pulled a cylinder instead. He was flying 140 hours a year, and he's wondering why he would get corrosion. Higher oil consumption isn't a corrosion problem, but the cam and lifter spalding do indicate it. These were unrelated problems, according to Mike. Paul thinks it's possible the damage was already in place when there was a previous IRAN. They settle on it being a lifter hardening issue, meaning poorly manufactured parts. 

Jim has a Mooney M20K and an instructor showed him a leaning procedure while in cruise at 9,000 feet. They set the manifold pressure to 30 inches, the RPM at 2300, and then pulled the fuel back to 11 gph. That's how he's been leaning ever since. CHTs are in the 360/370-degree range. He trails the cowl flaps to try and cool the CHTs if it's a hot summer day. If the TIT gets too high he'll enrichen it just a touch. Paul said if he adds more fuel and the TIT goes down, he's running rich of peak. 

Peter found some residue on the top of his intake valves on the engine on his 172N. He typically flies with autogas. He's wondering if can or should get rid of it, and if so, how to do it. Paul said people talk about it, but he's never done it. They suppose it's not carbon, but probably coked oil. They suggest a wobble test if he's really worried, but generally they think he can leave it alone.