March 2013

In this month's ShopTalk we will discuss the ever perplexing subject of preventive maintenance. We will talk about your Mooney engine and its accessories, and when to repair or overhaul these items before you are stranded at a far-away airport with a broken component .

Those of us that repair aircraft for a living see less new components and more overhauled components these days. A big factor here is that prices for new components are much higher than used (rebuilt/overhauled).

Each manufacture has developed time limits on their respective components that are published for maintaining their product in proper operating fashion. These time limits are not only hourly but usually calendar limits also. The key here is knowing when to complete preventive maintenance on which component and when each different component is due in order to budget for this cost.

Most of us fly our aircraft under FAR 91 (for pleasure) and not under FAR 135 (for hire). Under FAR 135 the operator must comply with all manufacturer's recommendations along with all FAA requirements. Those of us that fly under FAR 91 need only to meet FAA requirements.

An example is the FAR 135 operator having to comply with the calendar time limit for overhaul of a propeller even though it has not reached the hourly limit. So every 5 or 6 years, the prop is removed for overhaul, even though it has not yet reached the 1,500 hour time limit. An FAR 91 operator is not required to meet the calendar or hourly limits. Overhaul is based strictly on condition at annual inspection unless there is a FAA mandatory requirement for that prop. This example also applies to the engine and its accessories.

Trying to tailor a preventive maintenance schedule for a FAR 91 operator that won’t break the bank yet not leave the airplane stuck far away from its home airport depends on a lot of factors. Some of these that need to be taken into account are:

  1. Is the plane hangered?

  2. Is the plane near the ocean or salt air?

  3. Is the plane flown at above 12,000 feet MSL most of the time?

  4. How many hours per year is the plane flown?

  5. Is the plane flown under IFR conditions much of the time?

  6. Is the plane turbocharged?

  7. In what condition are the engine and accessories?

With the above questions in mind we will talk about the following items:

  1. Magneto(s).

  2. Vacuum pump.

  3. Alternator.

  4. Starter and drive.

  5. Cylinders.

  6. Prop.

  7. Prop governor.

  8. Fuel system – Pump/injectors/ carburetor.

  9. Exhaust system/ muffler.

  10. Turbo/ waste gate.

  11. Turbo scavenge pump/ check valves.

  12. The engine itself.

The first step in this process is to review the engine log books. Starting with the most recent log entry work your way backwards. Record the date and tach time when each of the above components were overhauled or had a 500 hour servicing completed. We are not concerned with repairs to components, we are looking for 500 hour servicing or overhaul by certified repair shops. Parts repairs do not affect the wear on components.


Over the years Mooneys have come with a variety of magnetos installed on their engines. Currently there are three styles of Bendix (TCM) magnetos and one of Sick magnetos used on our Mooney aircraft.

Bendix (TCM): The early M20 series aircraft came with a Lycoming O360 or IO360 four cylinder engine. These engines came with S20 series individual magnetos. These mags when new back in the 1960s and since have had a few airworthiness directives (ADs) against them. Nevertheless, in general they have proven very reliable. The M20A-G did not come with a impulse coupling on the mag so this is not a concern when discussing these magnetos.

None of the M20A-G aircraft were factory turbocharged so high altitudes were not a factor on magneto wear and tear. There were some STC turbo kits installed on these aircraft and if you have one of these you must treat your magneto maintenance more aggressively then a non-turbocharged engine.

Non-turbocharged aircraft: If you can determine the condition of your magnetos, and you are sure they were properly overhauled recently, then these magnetos will normally give you a safe 800 hours. Of course if the overhaul is not recent or is questionable then you should complete a proper 500 hour servicing on each magneto. This will give you a good starting reference point.

For turbocharged aircraft: I can’t overemphasize the need for completing a proper 500 hour servicing every 500 hours. Flying at high altitudes the low air pressure (15,000 feet ~ 8 psi) leads to flash-over in the magneto. This can be noticed in flight as an intermittent skip or misfire of the engine. Typically the engine won’t misfire for this reason at lower altitudes.

Bendix (TCM) D2000/3000 series dual magnetos: When this magneto was introduced to general aviation in the late 1970s it had a number of teething pains. It was hit with one AD after another and soon developed a bad reputation for reliability. This magneto came with a impulse coupling for starting and this coupling requires an AD mandated inspection every 500 hours. This is not a bad thing because this magneto is reliable for 500 hours of service before it needs a proper 500 hour service and coupling inspection. These magnetos have become expensive and difficult to properly service but are still reliable if serviced every 500 hours.

Slick 6200 series magneto: This magneto was installed on most Lycoming engines when TCM purchased Bendix Magnetos back in the 1980s. If you have a factory Lycoming engine on your airplane built after the mid 1980s it probably has these magnetos on it (except J model). This magneto was designed for low altitude operation and is not as robust as the Bendix S20 series magneto.

As most owners of TLS Bravo or M20K models will tell you, one can consider themselves lucky to get 500 hours of trouble free operation out of this magneto. Even though pressurized, it is not happy in the flight levels. It takes about 35 kilovolts for electricity to jump 1 centimeter at sea level; at 20,000 feet it takes only 18 kilovolts. One must always complete a proper 500 hour service at 500 hours or possibly be stuck at a far away airport with a bad magneto.

I had one TLS customer that flew a lot and we kept spare magnetos in stock, ready to change out. This same magneto on a non-turbocharged aircraft may go 700-800 hours safely.

Bendix (TCM) S1200 series magnetos: Bendix (TCM) made a large magneto for the TCM and Lycoming 520-550 and 540 and a few 360 engines. This magneto was very robust and could safely go 500 hours even on a turbocharged engine. On a non-turbo engine I was not surprised to find one with 1000 hours on it and still running OK. I think that with this magneto on a turbocharged aircraft, you still will want to do 500 hour servicing; non-turbocharged - 700 hours. Remember: if it’s a Bendix (TCM) magneto and has an impulse coupling it has an AD against it; remove and inspect every 500 hours.

VACUUM PUMPS: Over the years a number of manufactures have made dry vacuum pumps. Back in the 70s and 80s the main manufacturer was Parker aerospace with the 211 series the most common pump. These pumps could typically go 800 hours reliably if the drive seal was not leaking oil into the pump.

After numerous law suits, Parker got out of the vacuum pump business. For the last 30 years, first Champion then Rapco, Sigmatek and Tempest have built these pumps. The bottom line with any of these pumps is never install a rebuilt pump as they rarely last more then 200 hours.

If you fly IFR or if your autopilot relies on the vacuum pump always install a new one no latter then 800 hours and make sure the drive seal on the engine is not leaking oil into the pump. If this seal is leaking get it fixed as oil destroys dry vacuum pumps.

ALTERNATORS/GENERATORS: Early M20 aircraft came with a Delco 50 amp generator system and there are still a few of these flying around. These were robust systems and being all mechanical the regulators were bullet-proof, but they do not have the output of an alternator.

It’s not uncommon to see these Delco generators running well at 1000 hours and full of oil from a leaky engine. I would suggest not pushing this generator past 1000 hours though. Complete a proper 500 hour service by 1000 hours or sooner.

There are two STC kits available to replace your generator and both are good kits. The first on the market is the InterAv 50 amp alternator. The other one is the Plane Power alternator kit. Both are robust systems that use electronic voltage regulators so power at low engine speeds is much better than any generator system.

The InterAv will easily go 1000 hours trouble-free and the Plane Power will usually go to TBO trouble-free. They are both good systems but installation may require replacement of the generator belt which means pulling the prop.

Prestolite made 60-80 amp alternators for many years but has since gone TANGO UNIFORM. Kelly Aero Space has taken up the slack. The gear driven ALX series alternator on the TSIO360 TCM engine will normally go 500 hours but not much more than that. The shock drive on this alternator when new will last 1000 hours or so. Always due a proper 500 hour on this alternator at 500 hour and just replace the shock drive at 1000 hours with a Kelly or Drake rebuilt drive. A new TCM drive is over $1,400 but is not necessary for reliable operation.

The belt-driven Prestolite alternators like on the M20J, 252 and the Bravo are pretty reliable. The early M20J was notorious for the diodes going bad; when a load was placed on the alternator the voltage output would drop below battery voltage and discharge the battery.

The 252 belt-driven alternator is reliable and will go 800 hours before a proper 500 hour service must be completed. The M20M Bravo and M20TN alternators should have a 500 hour service at 500 hours. These alternators will last longer if the plane is not flown often in the flight levels. However, flight levels are where the Bravo and M20TN were designed to be operated, not at lower altitudes.

The M20S uses a gear driven alternator in the front of the engine like the M20TN. This alternator is very robust but it should get its bearings greased every 500 hours, so complete a proper 500 hour service on it at 500 hours. This will save you money in the long run.

STARTERS AND DRIVES: The TCM engines use a internal starter drive that looks and acts like a Chinese finger trap. When the electric starter motor is engaged this spring grabs onto a shaft that is interconnected to the crank shaft gear. When the starter is released the spring relaxes and releases the shaft thus disengaging the starter from the engine.

This system is very reliable but it needs a bit of spring back in it and a permanent magnet starter motor does not have that. TCM only recommends a field coil type starter for these systems.

Occasionally I will see a slipping prop (the starter is running but the prop is not moving) when the starter is engaged. This usually means it time to replace the drive spring. Generally, however, these systems are reliable and usually make it to TBO.

Lycoming engines use a starter and drive that is external; the drive is exposed to the elements. A permanent magnet starter is a good option instead of the field coil type.

Permanent magnet starters spin the engine faster making hot starts easier, and they save about 9 pounds in the front of the engine. Most of the permanent magnet starters reliably make it to TBO.

The field coil starters used on pre-1988 aircraft were subject to heat soaking from the engine and would work marginally when hot. The drives were subject to the elements and would not throw out to engage the flywheel. This would require spraying the drive with a cleaner and reapplying lube to it. Also with a weak battery the drive would not spin fast enough to fly out and engage the flywheel. A permanent magnet starter solved all these problems. Besides, what Mooney owner would not want an extra 9 pounds of payload?

CYLINDERS: There are a number of choices when it comes to cylinder selection whether you have a Continental or Lycoming engine. ECI (Engine Components Inc.) offers cylinder kits for some Lycoming engine models and there are plenty of shops that offer rebuilt chrome cylinders for just about any aircraft piston engine out there. Both TCM and Lycoming also offer new cylinder kits. But buyer beware, not all cylinders are created equal.

Most factory-new Lycoming cylinders are nitride hardened on the barrel portion of the cylinder assembly. This gives the cylinder wall extra protection from wearing out. TCM new cylinders are not hardened and therefore tend to wear out-of-round near the exhaust valve area before you get to TBO. This is especially true on TCM turbocharged engines. ECI makes plain and Cermanil coated cylinders. On low horsepower engines (180 or less) these cylinders work OK but are not as good as factory-new. Overhauled or chrome cylinders are what you put on your high time engine to get to TBO, not on a freshly overhauled engine.

The problem with overhauled cylinders is you don’t know if the cylinder was new in 2006 or 1966. Total time is not kept on these items and that fresh overhauled cylinder may have had 6 overhauls before you bought it.

Obviously the chrome or overhauled cylinder is going to be the cheaper to purchase but this is one area you want better quality which you rarely get from an overhauled cylinder. The factory-new cylinders are the best but are typically the most expensive. ECI has had their teething pains over the years while Lycoming and TCM have been building cylinders for their engines forever and have the process figured out.

When overhauling a customer’s engine I insist on installing factory-new cylinders.

PROPELLERS: Mooneys came with either Hartzel and McCauley props. There are also a number of STC kits available for changing props. A German company, MT Propellers, also offers composite prop kits for some Mooney aircraft. The advantage of the composite 3 blade prop is it weighs less than a standard aluminum 3 blade prop.

I am not completely sold on the composite prop for part 91 operators. I think the cost of ownership is not worth the benefit (just my opinion). Hartzel props are in my opinion a bit more expensive to operate then a McCauley prop and in general have more ADs against them.

Both Hartzel and McCauley make a quality product. My experience over the last 33 years is that the McCauley prop needs less maintenance and is more affordable over the long haul.

PROP GOVENORS: In the early 1960s Mooneys came with a Woodward prop governor. Later Mooneys had a Hartzel prop governor. It is difficult to find any new affordable parts for them and generally I have found it frustrating to get them overhauled to provide any kind of leak free operation. A typical prop governor should go to the ehgine's TBO. At overhaul, replace the governor with a new PCU 5000.

The Woodward and Hartzel prop governors were a good product in their day (1950s) but like most airplane engine parts, they are old and have been overhauled too many times. Like cylinders, no total time is kept on these items and new parts are scarce at best. A typical overhaul on these items: the best old parts put together with a new gasket kit and run on a test stand.

McCauley also makes prop governors which have proven to be very reliable. A McCauley prop governor can be overhauled with good results and provide many years and hours of trouble-free operation.

FUEL SYSTEM – Pumps, injectors/carburetors: Lycoming engines came with two different types of fuel pumps and both were very reliable. The 360 series has a diaphragm type pump and the TIO 540, a rotary pump. There have been manufacturing problems with both over the years but it is not uncommon for either pump to go to TBO. Just watch for fuel stains on the pump as this is a sign of impending failure.

Until the M20E came along in 1964, Mooneys were carbureted. The original Marvel-Schebler carburetor was reliable but is now showing its age like the Woodward prop governor. A number of companies have come and gone including Marvel-Schebler. In 2005, Marvel-Schebler improved their design and now produces rebuilds, overhauls and new carburetors.

The M20E model introduced fuel injection utilizing a Bendix RSA 5 series injector servo. This system allowed for individual injectors at each intake port. These systems have undergone some product improvement over the last 50 years and are reliable. A typical RSA 5 servo will go 15 years or to TBO. The fuel injection nozzles need to be cleaned every 100 hours to insure proper operation. The only adjustment on this system is the idle mixture and speed.

TCM: Mooneys with TCM engines are fuel injected. TCM has its own fuel injection system that also has individual injectors at each intake port. Unlike the Bendix system, the TCM system is very adjustable and different injectors can be used on most TCM engines to provide more or less fuel to an individual cylinder.

TCM publishes a list of engines and the nozzles and flow dividers that may be installed on them. It is not uncommon to find a mix of different size nozzle on an engine. Like the Bendix system, the TCM nozzles should be cleaned every 100 hours. Always be sure to reinstall each nozzle back to the cylinder it came out of.

Early M20K aircraft came with a TSIO 360 GB engine. TCM has been slowly converting all of these engines to an LB series engine. The fuel injection on the LB is a better system. It is becoming difficult to find some GB series engine parts for the fuel injection system.

On TCM engines the unmetered fuel pressure is field adjustable. TCM SID 97-3 shows all the engines and their respective fuel pressures. If you have not had this checked for accuracy it might be a good idea to get it done. As the fuel pump wears the pressure will drop. Also when the engine is replaced or overhauled, the fuel pressure must be reset correctly.

EXHAUST SYSTEM/MUFFLERS; All non-turbocharged Mooney aircraft came with a central muffler and four header pipes with a tail pipe exit for the exhaust system. Over the years the manufacture has changed and so have the systems.

The muffler needs to be inspected at each annual to verify the integrity of the flame tubes inside the muffler and to look for cracks and bulges. The only way to do this is to remove the shroud that covers the muffler and the tail pipe. Like the Woodward governor these exhaust systems are getting old and most have been rebuilt many times in the last 50 or so years. Most new mufflers will go to engine TBO but it's anyone’s guess how long an old muffler will last.

Any leak in the muffler system such as a cracked muffler or a torn outlet hose to the heater box can lead to carbon monoxide entering the cockpit. Another problem is flame tubes coming apart inside the muffler and blocking the tail pipe outlet of the muffler resulting in a loss of horsepower. Either scenario is dangerous, so track the time since last overhaul on the muffler and don’t let it go more than TBO on the engine.

An excellent time to get the muffler overhauled is when the engine is out for overhaul. The header pipes used to crack at the base of the cylinder flange, but most have been updated by welding reinforcement in this area thus resolving the problem. The mufflers are still susceptible to cracking where the header pipes fit to the muffler. On pre-201 Mooneys the ball joints in this area wear out and break. When this happens the hot exhaust goes right in to the engine compartment and could cause a fire. Inspect your exhaust system carefully every annual.

There is one more option besides rebuild: Power Flow makes new modern tuned exhaust systems for Mooneys. These systems will typically give you 1-2 inches of manifold pressure over a stock system. If you are looking at replacing your existing system it might be worth the extra money to get the extra performance.

Turbo exhaust systems do not usually have a muffler (some Rajay kits did) as this would create the improper back pressure for the turbo to work correctly. They do have one or more shrouds like the muffler to collect heat for the cabin heater. These areas must be inspected for cracks and bulges. Turbo exhaust systems unlike non- turbocharged systems run cherry red hot in cruise and any failure will cause not only a loss in power but a fire. Always pressure check these systems for cracks at each annual with soap bubbles.

If you run your Mooney turbocharged engine at or above 75% constantly and set the fuel flow to the book numbers for that power setting you will be changing exhaust components and cylinders on a regular basis. When operated at a normal 65-70% with a TIT lower than 1600 degrees, one can expect the turbocharger and waste-gate to go 1300 hours or more. I have seen some make it all the way to TBO. Proper leaning of a turbocharged engine will make it less expensive to own, it is just that simple.

TURBO SCAVENGE PUMP/CHECK VALVES: All Mooney turbocharged engines have some form of scavenge pump. This pump draws excess oil out of the turbocharger bearing/bushing so the turbo will not flood with oil and pump oil into the tail pipe or intake system. The pump is located above the turbocharger and therefore must have a good suction capability to draw oil up out of the turbo and return it to the oil sump (usually into the accessory case). If this pump is not overhauled properly there will be overflow oil burning in the tailpipe and the pump will not make it to TBO. This is one place where the factory remanufactured or overhauled engine is a bargain compared to a field overhaul.

Parts for these pumps are expensive and the Rajay pump parts are almost impossible to find. A lot of times the overhaul shop will just measure and test the pump instead of installing new parts. The T drive on the 252 is a classic example of expensive parts to replace: New TCM gears for this puppy will run you over three-thousand dollars!

Turbocharger oil check valves are often overlooked for inspection. Most turbo systems have an inlet and an outlet check valve. When the engine is running these valves are full open allowing oil to flow into and out of the turbo. The inlet valve closes at a higher pressure than the outlet valve. That way, when the engine is shut down, the inlet valve closes first shutting off oil to the turbo. The outlet valve remains open for a while allowing the scavenge pump to draw oil out of the turbocharger. Then it closes preventing oil from draining back into the turbo. These items are engine parts but are typically installed on the airframe. When the engine is out for overhaul they should be replaced. Like the alternator shock drive on the TSIO 360 engine these valves are typically not included in your engine overhaul price. Two new check valves will set you back $1,200. New check valves will usually go to TBO.

FLAMABLE FLUID HOSES: On non-turbocharged aircraft these hoses should be inspected at each annual for flexibility and to make sure they are not heat soaked. The 200 HP Mooneys are notorious for the fuel line from the fuel servo to the firewall becoming heat soaked and ready to leak fuel onto the exhaust system. Fire-sleeved fuel lines will last 10-15 years. Turbocharged engines are another issue, these lines can be subjected to extreme temperatures and should be replaced on condition; if the fire sleeve is cracked or chaffed. Only the best lines should be used on the turbocharged aircraft. I am not a big believer in changing these lines just because of age. I think flight hours are a better way of determining the condition along with a good old grab and bend test for flexibility. Whenever the engine is overhauled this is the best time to replace all the hoses no matter what their condition is.

ENGINE CONDITION: One thing to consider when looking up the times on all the above components is what is the general condition of the engine? If you have a high time engine near or beyond TBO it may not be realistic to invest a lot of money fixing the accessories. You may be better off getting the entire engine overhauled. Use this article as a guide to address the items that aren't provided with an overhauled engine.

When it comes to the engine and the question of field overhaul vs. factory overhaul/remanufactured, I am now of the opinion that a factory engine is the only way to get all the new parts installed that are needed to get to that next TBO with minimal maintenance. It did not used to be that way. Years ago, when Superior Air Parts were making engine parts for TCM and Lycoming engines, the engine overhaul shops could compete with the factory price and quality because Superior Parts were more affordable and of the same quality as the factory parts. Now the engine shops have to purchase parts from the factories or ECI or use overhauled parts. That makes it difficult for them to make any money unless they use more used parts or reuse your used parts. The trade-off with the higher cost of a factory engine is less maintenance, therefore more flying.

As always if you have a question about this article or another ShopTalk, feel free to contact me at my aircraft repair shop at 307-789-6866 or via e-mail. Until the next ShopTalk, enjoy flying your Mooney.