A grab bag of unique questions come at Mike, Paul, and Colleen this month, including whether to buy new or overhaul, how prop stops work, what happens when you reduce from wide open throttle, and avoiding tiedowns. Submit your question to [email protected] for a chance to be on the show. Full notes below: Dale has a Seneca and he’s looking to the future and having to overhaul two engines. He’s wondering how to decide between factory new, reman, or overhaul. Not surprisingly, they suggest flying your current engines as long as possible if they are treating you well. When the time comes that you have to change engines, Mike said his general rule is that if the engine has treated you well to consider a field overhaul. If there’s a concern about the current engine, he said to consider a factory engine. More control over the process is another reason to do a field overhaul. Jim has a question about his L-3 with a Continental A65. He has an updated carburetor with a mixture control. A challenge with that engine is that you don’t get an onset of roughness when leaning. It just tries to quit, and without an electrical system, an in-flight shutdown isn’t ideal. He’s worried that a big stumble is startling and he pushes it too far rich again, putting him in the red box. Mike said there’s no need to go to roughness. You can lean only to the first indication of power reduction. Dubs has noticed that after leveling in cruise, when pulling the throttle back from wide open, it moves a significant amount before the manifold pressure changes. Yet in doing so he’s reducing his fuel flow. He’s wondering why this happens. Mike thinks it’s possible Dubs has a carb with an enrichment circuit, which gives more fuel at wide open throttle, meaning fuel flow will come down as soon as throttle is reduced. The hosts discuss how Dubs’ operating practice is how Cessna 182 pilots with 0-470 engines should operate to improve mixture distribution. The impact butterfly valves make is very non-linear, they say. The first 5 to 10 degrees of tilt won’t make a big difference, for example. Phillip is a maintenance tech in a shop that adjusted the low pitch stop of a prop based on the recommendations of the prop shop. He’s wondering why it was successful. Paul describes how a prop adjustment works, and why some airplanes don’t make full rpm until they’re down the runway a bit. Richard’s Rotax ran rough on a run-up, and after some troubleshooting he still hasn’t found the culprit. All winter it ran fine, but he’s concerned it will happen again in warm weather. Since this happened on both magnetos it’s likely not a spark plug. Colleen is wondering if the rpm range had an impact because the Bing carbs have three distinct operating ranges. If it happens again Colleen recommends isolating it and first checking the spark plugs, then maybe cleaning the carbs, and finally looking at the fuel delivery lines. Mike thinks it has to be a fuel system problem since it changes with temperature. Brennan has a nice Mooney M20J that he wants to continue to take good care of. He now lives in a very humid environment and can’t find a hangar. He left the airplane in his old hangar and can barely get to the airplane to fly it. He’s wondering what would be the least damaging practice—fly less or keep it outside. The hosts think it’s better to get the airplane closer and fly it while doing his best to keep corrosion away with freshwater washes, corrosion treatments, and maybe covers.

With two important airworthiness directives recently issued for Continental engines and Cessna Cardinals and 210s, Mike, Paul, and Colleen dig deep on the surrounding capacity and safety issues. Then they take calls on the limitations of engine monitors, and how normal can look anything but. Submit your questions to [email protected] for a chance to get on the show. Full notes below: Michael has a turbonormalized Bonanza and he’s concerned his system isn’t operating properly. When full throttle on takeoff it overboosts, so he goes to partial throttle, which lowers the fuel flow. The controller and waste gate were both checked with no change. Mike says it’s a very bad idea to limit the manifold pressure with throttle. Continental says overboosting by 3 inches is a non-event. What is a big event is limiting fuel flow. The fuel flow is determined by the upper deck pressure, which could be adjusted. Either way, Mike says that Michael can leave it alone and give it all the beans. Paul is shopping for an engine monitor and is wondering if the hosts have any advice. Of course they do! Mike recommends user-programmable alerts. Otherwise they recommend you buy the one that best fits in your panel. A slew of recommendations on how to use it follow. Laurie’s engine runs roughly in a certain rpm range unless she leans to peak EGT. The hosts soon learn that she operates from an airport at more than 7,000 feet. Mike thinks it’s likely this is normal behavior because the engine runs too rich at full power at such a high elevation. John thinks he might be experiencing morning sickness on his RV-7’s O-360 engine. He is noticing an increase of lead buildup each time he borescopes it. The CHTs are also too low, at around 300 degrees in the winter. He felt the engine was running rough for a few minutes after starting, as well. The hosts look at John’s photos and think his engine is perfect. Paul mentions that so long as the valve seats well, the gunk in the cylinder is fine. They offer a number of ideas on increasing his CHTs. Steve is frustrated with his engine monitor because he's experiencing what he believes are nuisance alarms. The issue is that his engine manual and POH have different numbers, and the engine monitor is programmed with the POH numbers. The engine monitor can be reprogrammed, but it’s expensive and requires input from a mechanic. This is mostly an issue with engine monitors that are certificated for primary replacement.

Mike, Paul, and Colleen debate the difference between a bribe and incentive pricing, discuss how much carbon in the oil filter is too much, counsel an owner how to keep his alternator belt on, and reveal what's in their go-bags. Email [email protected] for a chance to get on the show. Full notes below: Jim is finding a significant amount of carbon in his oil filter after oil changes on his Cessna 182. He wants to know if the carbon is a problem. Mike said the carbon itself isn’t a problem, but it’s indicative of something else that is worth tracking down. He said the oil is getting overheated, carbonizing it. It’s most likely from excessive blowby. They recommend compression checks and borescoping to see if he can find the culprit cylinder.     John flies a Mooney with an electronic ignition system, and he thinks the airplane is slower since the system was installed. Mike thinks it’s possible it wasn’t timed properly. They see it often because the electronic ignition system is timed differently than a traditional magneto. If the EGTs are up and CHTs are down, that's further confirmation.     Jim is frustrated with the alternator drive belt on his 182. It comes off the pulleys about once every 10 hours. Paul said it’s very common. Counterbalances on the crankshaft are a potential problem, but a last resort. Grooves in the pulley could also be the culprit, as could excessive play on the shaft on the drive pulley. Paul also suggests trying a solid belt instead of Jim's current segmented version.     David is trying to make a kit of tools and spare parts to take while on cross-countries, and he is looking for recommendations. Paul said he has two criteria. First is something you’re willing to change. The second is to take any special tools or parts that most shops don’t carry. Mike said he takes common-failure items for the specific airplane. On his 310 he carries a vacuum pump, for example. Colleen said she always carries duct tape and tie raps, a screwdriver in order to take the cowl off, and a first-aid kit.     Dustin has a controversial question about a recent interaction with a shop. During the buying process of an engine overhaul, an owner found out a supplier offered the shop $2,000 to the shop if the owner went with them. The owner found out thanks to the shop's honest disclosures, but questioned if this is an ethical practice. Mike thinks this is no different than a wholesale/retail markup. Paul said he understands why this feels different, but he thinks it’s legit. Mike recommends asking your shop what they are making on your part, and if you’re not happy with the amount to negotiate it.

This month Mike, Paul, and Colleen give an owner the ammo he needs to not overhaul his engine prematurely, help console an owner with super hot cylinders--maybe, console another with super cold cylinders, and give cover to a pilot who wants to refill his own oxygen. Send your comments and questions to [email protected] for a chance to get on the show. Full show notes below: Pat’s Diamond has one suspect cylinder. The mechanic said it has failed inspection, and needs to be replaced, but the engine is beyond TBO and they are refusing to fix it without an overhaul. The question hits right at the heart of some of Mike’s frustrations with shops and their lack of evidence-based practices. He suggests lapping the exhaust valve to bring the compression back up, and then keep flying it. Kirk wants to refill his own oxygen system, but it’s not covered specifically in preventative maintenance regulations. The hosts asks if you’re allowed to add oil, fuel, and air to the various systems. Of course you can. It’s servicing the airplane. Mike says there is no talk of servicing in the regulations, but of course we all do it legally. They view adding oxygen in the realm of servicing. Robbie doesn’t believe his CHT gauge in his Socata TB-10. The factory single probe gauge shows 500 degrees and rarely goes below 400. He’s wondering what he can do to make himself feel more comfortable that it’s a gauge problem. Colleen asks if he smells anything. She smelled burning oil when hers went beyond 420. The hosts agree that given his great borescope photos, and good oil analysis that he’s probably ok. They also suggest checking the engine grounding strap that goes from the crankcase to the firewall. It grounds the engine to the airframe, and without it the probe wire could be finding some interference. The paint would also change color at 500 degrees. Will is seeing exceptionally cold cylinder head temperatures on his Comanche. On a recent flight to New York, he saw temperatures in the high 140s during descent. He knows his probes are good, so he’s wondering if there’s a lower limit and if it's hurting the engine. After discussing a number of possible causes, they discovered that Will is going full rich on descent, which is absolutely contributing to the low temps. Mike said that while you may have to enrichen a bit in the descent, if you forget the engine will remind you by running a bit rough. That’s followed by a detailed discussion of leaning for the climb and descent. Carl flies a Cherokee 180 and is wondering if flying it on cold winter days with density altitudes below sea level could hurt the engine. The hosts agree that the takeoff mixture setting is so rich that there’s enough of a margin not to worry. Detonation could be a concern in certain experimental engines, but a normal certificated engine has a big detonation margin.

Did you know things live in jet fuel? These are the fun things you learn being a mechanic. Mike, Paul, and Colleen enlighten us on this strange fact, and tackle questions on leaning, burned exhausts, puddles of oil, and how not to set your airplane on fire when preheating. Email [email protected] with your question for a chance to be on the show. Full notes below: Chris owns a Piper Comanche with 1900 hours on the engine, and it that has developed an oil leak of one quart every 2.5 to 3.5 hours. Fuel tank sealant and an air/oil separator didn’t work. Paul says there’s no way he is leaking that much oil from a leak in the crank case. He suspects another issue. Mike said Lycoming has a procedure to slather a sealant on the case seam. Since there’s a lot on the belly Mike thinks it might be going out the breather. He suggests a ring wash. Lance flies a Cessna 185 and is worried about his leaning procedure. He’s recently replaced all six cylinders and is concerned his leaning procedure may have caused some problems. He’s worried that by learning until roughness and then enriching slightly he’s in the “red box.” Paul said if the engine is running rough, at least one cylinder has quit firing, so he's very lean at that point. Mike said the GAMI spread should be less than a gallon per hour. The GAMI spread is the difference in fuel flow between when the first cylinder peaks and when the last cylinder peaks. Assuming he only enrichens enough to stop the roughness, and no further, and his GAMI spread is good, he’s likely fine. If the CHTs are all below 400 degrees F and he’s less than 60 to 65 percent power, he has nothing to worry about. Chris number two asks about corrosion in fuel tanks. He works on turbine aircraft and often sees a brown staining on fasteners inside fuel tanks and he’s wondering whether it should be replaced. Paul said it’s only when the materials starts to degrade when you need to worry about it. He said a good rule of thumb is that if the part number imprint is still there that it can be left alone. Brad is wondering about pulling the prop through prior to starting. The general idea is apparently to move the oil around. Colleen said there’s no truth to any of it. You’ll scrape the oil off the cylinder walls if there’s any left. You can either preheat to heat the oil up on cold days, or you can pre-oil the engine if it’s been sitting a long time. Paul warns against pulling the prop through for safety. There’s no value in turning it backwards, and turning it forward can start the engine if you aren’t careful. Barry has a Tiger that had a muffler that lasted a long time when he ran rich of peak. Since running lean of peak or near peak his flame cones have burned out within 400 hours. Colleen talked to a local exhaust rebuilder who said he believes running lean of peak is burning up exhausts. It’s not because of the exhaust gas temperature, per se, but more likely the oxygen content of the flame at those mixtures. Jeff had a student with a Cessna 172 that he thinks has a tachometer from a Piper. It was replaced in 1993, and had been correctly signed off every year since. He’s wondering how that happens and what the pilot’s responsibility is in this case. Mike, Paul, and Colleen agree that an IA wouldn’t necessarily catch it on the inspection, although instruments and markings are part of the annual inspection checklist. Paul said he’s mostly concerned with the redline, and not necessarily the green arc.