Ask the A&Ps

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

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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.

What exactly should we be looking for in our cylinders? Plus torque tales, making TBO, and overzealous manufacturers.

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Full show notes below:

Jared asks what he should be looking for with his borescope. He’s seen bad valves and what that looks like, but he’s also hoping to see what bad scoring and other things. Colleen stresses to focus on what goes wrong with a cylinder, and being able to identify those attributes. Things like broken rings, piston pins, detonation signature, etc are identifiable, and can be examined. Paul said rust is always something to look for, but most cylinders have some. Knowing how much and why it’s there is what matters. Mike said rust would cause him to consider the camshaft on an airplane in a pre-buy situation, for example.

 

Chad has a new Cessna turbo 206. He wants to be sure to get to TBO and then some. Paul said the one thing he needs to do is fly as often as possible. He is flying 400 hours a year, which the hosts love. He asks if he
can fly a maximum continuous power, and the hosts agree that he can, so long as his cylinder head temperatures are within spec. The book tells Chad to lean to peak turbine inlet temperature, and not to run lean of peak. He wants to know if this is a real threat or a hollow one. Once again, the hosts agree that it’s a hollow threat, and that he should operate lean of peak if he can. They also discuss the myth of turbo cooldowns. Mike said George Braly instrumented a turbo and found that it actually got hotter as it sat on the ramp “cooling down.”

 

Serrhel is sick of the Continental maintenance schedule. He has a Cirrus that is under warranty, and he’s required to do the maintenance as scheduled. At 300 hours an injector cleaning was required, and only a few
months later, the injectors had to be cleaned again during the annual. Cirrus and Continental required it, even after some pushback. Paul said manufacturers don’t buy into the probability of maintenance induced failures or in the concept of reliability centered maintenance. The discuss the reasons why manufacturers think this way, and Mike said a conversation with a factory representative taught him that they basically don’t trust GA pilots and owners to maintain aircraft at a high level.

 

Patrick is throwing down a challenge to Paul. He said Paul always stresses that when tightening case through-bolts, you torque simultaneously with torque wrenches on both sides at the same time. Old Continental videos say the same, but the video shows the technicians only torquing on one side at a time. Despite the guidance, Paul said it doesn’t make sense to put a torque wrench on both sides at the same time. Mike said if you put a torque wrench on both sides, one side will be torqued dry and hit the pre-load spec too early. Mike and Paul then get into a debate about how the logbook entry should be made when if you decide not to follow Continental’s advice. Patrick further mentions that the Continental service manual doesn’t say it should be simultaneously.

The definitive guide to owner maintenance, slipping starter adapters, and close CHT tolerances.

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Creative leaning techniques, rusty cylinders, and odd manifold pressure indications are on tap this time.

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Old engines, rusty airplanes, and a strange valve incident are the puzzlers for Mike, Paul, and Colleen this episode. Send your questions to [email protected] for a chance to get on the show.

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Full episode notes below:

John has a Beech Musketeer who had an unusual situation with his valve. The valve seat separated from the cylinder barrel and dropped down, striking the piston crown. He's wondering if he did anything to cause this, despite never exceeding 425 degrees CHT. The hosts agree that it was probably a manufacturing error, even though the cylinder had a few hundred hours on it. Mike said the only way this can happen is with a manufacturing problem or a high heat event.

Larry has an early SR22 with 3,300 hours on the engine. It's not in need of an overhaul now, but Larry has read those early SR22 cases are more robust, and he's wondering when the time comes if he should overhaul or do a factory reman. The hosts aren't aware of any particular issues that make cases from that generation better, but they do offer some sound advice on the reman versus overhaul question. Mike said that if the engine has been treating him well that Larry should overhaul it. And if it's been a lemon, send it off and get a new one from the factory. Larry is a little worried about resale, since people are skiddish with high-time engines. Mike suggests that an airplane with run-out engines is the best investment because it's been fully depreciated. Any additional time is essentially free.

Terry has been looking for a 182 and he saw one in California with corrosion. He wonders how much corrosion is too much. Paul said that according to Terry's photos, he wouldn't think twice about buying the airplane. The general rule is that you can take off only 10 percent of a structure and not worry about it. The skin on top of the wing where the corrosion can be seen is only 25 thousandth of an inch, which means you could only take off 2.5 thousandth of an inch and still use that skin. White splotching can be seen in the photos, and Paul said it's common for airplanes of that vintage, and not to repair it. Instead, he recommends spraying it with ACF-50 or Corrosion-X every few years. Doing so will stop the spread and not allow any further damage.