Ask the A&Ps

Sticky valves, sleepy valves, and valves destined for the trash are on tap this episode. Email [email protected] for a chance to get on the show.

Join the world's largest aviation community at aopa.org/join

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.

Email [email protected] for a chance to get on the show.

Join the world's largest aviation community at aopa.org/join

Full notes below:

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.

How much should a mechanic tell a client during an annual? Mike, Paul, and Colleen handle this question and more.

Email [email protected] for a chance to get on the show.

Join the world's largest aviation community at aopa.org/join

Full notes below:

Justin flies a Twin Bonanza and cylinder 5 on his left engine takes as much as a minute to fire up and start running. It comes online fastest if he goes very lean quickly after starting. He's pulled the valve cover and springs off, and it's not a sticky valve, and he's reamed the valve guides. Mike wonders if it could be a primer problem. Justin disconnected the primer line, ran the boost pump, and checked for leakage and couldn't find any. Paul suggests taking the line off, capping off the injector, and then trying it. 

Jorg is trying to make sense of his data. He has a K35 in Austria and he has GAMI injectors and an engine monitor on his IO-470. He has a low CHT on the number 6 cylinder, and it's the first one to go on the lean side, and it shuts down first if they go very lean. An induction leak test seemed fine, and his GAMI spread is less than a gallon an hour. The valve was also lapped. Mike said a low probability culprit could be if the bleed air holes in the injector nozzle were plugged, since they don't seem to have an impact at wide open throttle, but would at a reduced throttle. 

Mark saw a Youtube video and is now wondering if there's danger lurking in the alternator. The video mentioned how an alternator elastomer coupler failure could lead to a catastrophic engine failure. Paul said the installation is critical because of some critical components. Mike thinks the video relies on old information. He said Continental used to employ a spring, which would come apart and throw large chunks of metal into the engine. The coupler is meant in part to protect the engine if the alternator seized, but sometimes the coupler would fail and cause its own failure. The newer versions have an elastic or rubber piece instead of a steel spring, which shouldn't cause an engine failure. 

Chaz is an A&P/IA and he wants the team to weigh in on the debate as to whether the inspector should give pilots a full list of squawks or only the airworthiness issues. He personally thinks he should give the whole list so the owner knows where he stands. The hosts agree that the full list is preferable. The mechanic is giving a full slate of options, and not a required list. Airworthiness items can be listed separately or be flagged.

Quick corrosion, long-lasting engines, and mobility mods are on tap for this episode.

Email [email protected] for a chance to get on the show.

Join the world's largest aviation community at aopa.org/join

Full episode notes below:

Patrick is looking for the right fit on a potential aircraft purchase. He had a shoulder replacement and lost some mobility in his right shoulder. He’s wondering if he could get an accommodation on things like flap controls. Paul suggests he look for an older Cessna with the progressive flap switch, not the one with pre-selected detents. The hosts thing that up/down progressive switch would be a minor alteration and just a
few wires. The pre-select flap lever is probably a major alteration and a lot
of work because there’s a lot going on behind the panel.

 

Jeff has a Maule M7 on floats and is battling corrosion. Recently he did a salt water landing, sat for about 3 hours in the water, flew home, and his left main gear didn’t rotate as he landed. He saw that the main forks had a bloom of corrosion that froze the wheel. He washed everything in fresh water, and then next day saw a bloom on the other gear as well.  He is wondering if he had a stray current given how quickly it developed. Mike thinks it’s unlikely because if the battery if off it’s completely isolated from the rest of the system, meaning their shouldn’t be a way for the battery to provide electrical current anywhere on the airframe.

 

Lindsay recently purchased a Piper Lance and wants to make sure she keeps the engine going as long as she can. They go over the basics and make sure she is boroscoping the cylinders, fly it regularly, etc.

 

Mark is wondering how soon is too soon to put in cowl plugs after flying. He has a Cessna 206 and he’s wondering if he can put in the cowl plugs right away. The concern is about the plugs, not the engine, Paul said. The hosts all agree that he's fine to seal the cowl off as soon as he likes.

Is going past TBO more expensive? Plus fuel vents and turbocharger temps. Email [email protected] for a chance to get on the show.

Join the world's largest aviation community at aopa.org/join

Full episode notes below:

 

Mike wonders if running past TBO actually costs more. He has
a Mooney and has heard that overhauls far beyond TBO can cost more as a result
of having to replace more parts. That is an oft-reported myth, Mike says. The
only things that can cause an up charge on most field overhauls are having to
replace the case or the crankshaft. Otherwise it’s a fixed price. Paul says the
top engine generally goes into the trash. On the crankshaft, they usually just
have to polish it or grind it. There’s no repairing a crankshaft. If it’s bad,
it was bad because it had some other type of problem. You can go thousands of
hours on crankshafts. Mike said Lycoming had a white paper on their website
that said crankshafts are generally good for 14,000 hours. Cracks on the case can
be welded.

 

Mark has an early 182 and he’s having issues with the fuel
caps properly venting. He has noticed that once you fill the tanks with cold
fuel, there doesn’t appear to be an outflow vent. Paul said there’s a small
weep hole that allows the expanded fuel to vent. But Mark’s tanks still aren’t
venting. He pulled it out but didn’t seem to find a weep hole. He said it looks
original and has an early Cessna part number. If the fuel is pouring out it
needs to be replaced because the check valve is bad. The wing will balloon and
can cause structural damage without a weep hole. He said when he removes the
cap a big woosh of air will come out, indicating the fuel isn’t venting out as
it expands.

 

Jim is wondering how TIT and EGT intersect. He flies a turbo
Saratoga and has been experimenting lean of peak and rich of peak. He’s noticed
a significant difference between EGT and TIT. If the TIT is farther away from
the engine, he’s wondering why it’s hotter than EGT. He’s also wondering how
hot he can let the turbocharger get. Mike said TIT is hotter because the EGT
probe is only seeing gas flow for less than a third of the time, and only when
the exhaust valve is open. The EGT probe actually measures a “probe”
temperature that averages the temps over time. When the gas gets to the TIT
probe it’s a constant heat from all cylinders all the time. Redline on his TIT
is 1,650 degrees, which Mike said is a continuous operation limit. Paul asked
what the exhaust system is made of because that matters. He suggests not
exceeding the red line. In cruise, the lower you can keep the TITs, the longer
the system will last. Mike limits his TIT to 1,600.