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Flying a 360

 

December 2010

 

No, not flying a 360° turn. This month's ShopTalk will delve into the expensive world of owning, operating and maintaining a 500 hour to mid-time TCM TSIO-360 series engine. TCM, of course, stands for Teledyne Continental Motors, located in Mobile, Alabama. TCM was formed when Teledyne Inc. purchased Continental Motors in 1969.

The TSIO-360 engine, first certified in 1966, has been used by many airframe manufacturers. The Cessna T337 Sky Master, Piper TurboArrow and Seneca II - V, as well as the Mooney M20K, all used some version of TSIO-360 engine. Over the years this engine has been refined to have an automatic wastegate system, turbo intercooler, a second alternator or a Freon air conditioning compressor (belt driven).

History: The original TSIO-360 engine was a 1400 hour TBO engine with light crank cases and light connecting rods. By now most have been converted to 1800 hour TBO engines or come from the factory that way. The higher TBO is identified by a “B” added to the variant letter, i.e. a TSIO-360-F (Turbo Arrow) would be a 1400 hour engine; a TSIO-360-FB would be an 1800 hour engine.

The Mooney M20K started life in November of 1978 as a 231 with the TSIO-360-GB engine. Later versions had the TSIO-360-LB engine which ran cooler cylinder head temperatures (CHT) due to fuel injection and induction system changes. It also added Slick pressurized magnetos. The lower temperatures improved the -LB engine longevity so much so that TCM, when overhauling a -GB engine, would upgrade it to a -LB. In 1986, the M20K evolved into the 252 adding completely enclosed landing gear, continuously adjustable cowl flap and the TSIO-360-MB engine.

The -MB engine was a big improvement from previous TSIO-360s because it came with an advanced air induction system which alleviated most of the fuel injection and high CHT problems. An intercooler with a Garrett AiResearch turbocharger and automatic wastegate made this engine completely different from most other TSIO-360 engines. The -MB engine developed the same amount of horsepower as the -LB but did so at 36˝ of manifold pressure instead of 39.9˝.

The final Mooney evolution of the TSIO-360 was the SB version in the Encore. Not many of these aircraft were produced but TCM upped the takeoff horsepower (time limited) by increasing the manifold pressure. The maximum rpm was reduced to retain the 1800 hour TBO.

Turbocharged TCM engines are typically boosted above 29.92˝ of manifold pressure to obtain 100% rated horsepower. Turbochargers compress engine inlet air raising its temperature. This in itself leads to higher cylinder head temperatures (CHT) and oil temperatures. The back pressure in the exhaust system required to spin the turbocharger up to speeds to get higher manifold pressures also raises temperature and traps heat in the exhaust system leading to even higher CHTs. An intercooler helps to lower the compressor discharge temperatures as will an automatic wastegate which allows exhaust gases to bypass the turbocharger turbine. The wastegate automatically modulates to run the turbocharger at maximum efficiency, resulting in lower turbocharger RPM and exhaust back pressure. Maximum efficiency means increased critical altitude, the maximum altitude where the engine will still develop 100% rated horsepower at full throttle.

Mooney, like other aircraft manufacturers publishes in the POH maximum never-exceed oil temperature, CHT and TIT numbers. However, in reality the airplane owner wants to go fast without adversely affecting the longevity and reliability the engine. If you operate your engine one needle width from red-line on oil temperature, CHT or TIT, do not be surprised when your mechanic gives you a bill for a complete top overhaul at 300 hours or less. Another consideration with any (older) aircraft is that gauges, especially analog gauges, may be highly inaccurate. So what are real-world operating procedures for a TSIO-360 to make it to mid-life before needing a top overhaul while not flying around at Mooney 201 speeds? A good rule-of-thumb is to stay about 1/8” below red line on CHT, TIT and oil temperature. For longevity, the lower the better.

Cylinders: Unlike most Lycoming cylinders, the TSIO-360 cylinders are not nitride surface hardened. Comparing nitrided Lycoming cylinders to TCM cylinders is like comparing apples to oranges, they are both cylinders and both round but their use in an engine is subject to differing operational constraints (orange pie ala mode?). Manufacturers set ring tension and cylinder hardness of the piston ring-cylinder assembly to achieve the desired horsepower with least amount of blow-by and minimal oil consumption while providing long service life (hopefully)..

The higher continuous (such as during climbout to altitude) power settings concentrate heat in the exhaust valve area of the cylinder wall; over time, this causes the cylinder wall to wear into the shape of a football instead of a round cylinder. Then the piston rings migrate (they are free rotating) so that the ring gaps line up at this worn section near the exhaust valve. The allows the compressed and combusted air mixture to blow-by into the crankcase. This pressurizes the crankcase, pumping the oil out the breather tube and onto the belly of the aircraft. Compression is continuously lost out the breather instead of at the proper time out the exhaust valve where it would have made horsepower.

With Continental engines you will see this on an oil analysis. It shows up as high iron and it's indicating wear of the cylinder wall. I have seen TSIO-360 engines with as little as 200 hours with this condition that now need to have cylinders changed, yet in this same paragraph I can say one of my customers has an -MB engine that has over 1100 hours with the original cylinders on it. It’s all in the power you chose to use, the TIT and CHT temps that you chose to use. Lower power settings, lower temperatures. Of course your plane would be slower and most Mooney owners want to go fast! You can see it’s a trade off, speed or engine longevity, the choice is yours as the operator.

What are my options when a top overhaul is needed?

Option one: Buy six new TCM cylinder kits (which it’s the best way to go) and you must budget $8,000 to $9,000.00 for parts and $2,500 to $3,500 in labor with about one week of down time.

Option two: Have your mechanic pull all your cylinders and send them out to be bored 0.015”oversize and to overhaul the heads. Budget $7,000 to $8,000 for parts and again $2,500 to $3,500 labor; three to four weeks of down time.

Option three: Exchange your cylinders for chrome, Cerminil or steel and replace the pistons and rings. Any more, I don’t really consider this a viable option because the cylinders you may be getting in exchange may have been overhauled five or more times. No one keeps total time of these parts. This option is only used on high time engines that you don’t want to put a lot of money into. And don't waste your money doing a complete top overhaul on a worn-out engine even when it's near TBO!

Alternator: All M20Ks came with a gear-driven Prestolite alternator with a rubber shock drive. This alternator tends to run hot as it is located at the bottom of the accessory case on the back of the engine so a cooling shroud is desired. Most K models came with one. These alternators reliably last about 500 hours. The 231 has only one alternator so be sure to complete its 500 hour service on schedule. A new shock drive for this alternator is over $1,800; a rebuilt, around $800. A new one will typically last 1,000 to 1500 hours. If your engine is involved in a prop strike, make sure this shock drive is replaced. The alternator itself will cost around $300 to $500 to service plus the labor to remove and reinstall if the shock drive passes the torque test.

The 252 and Encore came with a second belt-driven alternator along with the standard gear-driven alternator that the 231 has. The pulley in the back of the engine comes off of a T-drive starter drive assembly. The second Prestolite alternator that the T-drive pulley turns via a belt-drive has very good reliability and should easily go 800 hours before needing any repair. The 252 and Encore both came with cooling shrouds on the back of the second alternator. The cost for this belt-driven alternator for 500 hour service is around $300 plus the labor to remove and replace (R & R) it. No shock drive to worry about.

T-Drive: The next accessory on the back of -MB engines is the starter drive scavenge pump T-drive assembly; a very expensive part to repair or overhaul. The 231 did not have the T-drive on the end of the scavenge pump and was much more reliable. The vacuum pump comes directly off the back. The starter drive and scavenge pump on the 231 would typically go to TBO, but that may not be the case on the 252 or the Encore. With the T-drive, it’s not uncommon to see the vacuum pump drive seal leaking at 700 to 800 hours, making a mess in the back of the engine compartment, spraying oil on everything.

Inside the T-drive, at midlife, it is not uncommon to find the bevel gears and scavenge pump gears completely worn beyond limits. Sometime around 2002, Teledyne Continental decided to change the Rockwell hardness on the T-drive beveled gears from Rockwell hardness #30 to # 65. These gears are close to $800 each and there are three of them. TCM on the -520 and -550 engines upped the hardness of the scavenge pump gears, but left the gears on the -360 at #30. Coupled to the T-drive beveled gears and under load, they prematurely wear out. The two scavenge pump gears are $700 each! Off the T-drive is also the vacuum pump and the starter motor. The T-drive is a very complicated sub-assembly and very expensive to repair. A new drive may make it to TBO, but an overhauled drive with any used serviceable gear probably won't. Also an overhauled drive may contain some old softer bevel gears.

Starter Motor System: The starter system on the TSIO-360 is typical for TCM but unique compared to Lycoming. The starter motor winds up a spring that acts like a Chinese finger-torture toy which grips a special shaft that looks similar to a commutator on a generator. The starter motor drives a worm-gear reduction to the finger-torture spring. When the starter is cranked, the spring grabs the commutator type shaft which is reduction geared to the crankshaft. When the engine has started and the starter motor torque ceases, the spring loses its grip and the commutator type shaft spins freely inside the expanded spring. This has been a fairly reliable system for Continental. The spring that winds around the shaft is affordable but the reduction gear and worm-gear are very expensive. Therefore, getting a good starter drive is really important on an overhauled engine. Again, overhauled means possibly used parts.

Turbocharger Scavenge Pump: The turbocharger scavenge pump gears we talked about earlier draw oil out of the turbocharger and lift it up to the top of the engine where it is dumped back into the crankcase. If the oil is not scavenged from the turbocharger it will fill up the bearing housing cavities and flood the turbocharger with engine oil. This results in oil entering both the intake and exhaust systems. Worn scavenge pump gears that can't draw a suction, can't scavenge oil from the housing cavity. Also turbocharger check valves that are improperly installed or worn can flood the housing cavity.

All the M20K aircraft have two turbocharger check valves which allow oil to flow through the housing but prevent oil in the scavenge pump line from draining back into the housing after engine shutdown. An air leak below the scavenge pump can also cause an oil-flooded housing. The inlet check valve opens when there is oil pressure and at a higher pressure than the outlet check valve. At idle (low oil pressure) the outlet valve will be open allowing the scavenge pump to draw all the oil from the inlet valve out into the scavenge pump and back into the engine. This is one of the reasons why you should always allow the turbocharger to spin down and cool off at idle for four minutes after landing. This gives the scavenge pump enough time to draw all the oil out of the lines. Assuming the valves are not leaking, the turbocharger will not fill back up with oil. Because the turbocharger is on the low point of the engine, oil will drain back to the turbocharger if the outlet valve is leaking or installed incorrectly. At the next engine start, the oil is sprayed out the tail pipe. The two turbocharger check valves frequently leak as they get hours on them or if they get held open with debris. Two new check valves can cost as much as $1,500 not including the labor to trouble-shoot and R & R.

Magnetos: The TSIO-360-GB series engine in the early 231 came with unpressurized Bendix magnetos. Critical altitude for this engine is only 15,000 feet and as long as you didn't fly regularly above this you would get good reliability from this magneto. Unfortunately the Bendix magneto has an AD against the impulse coupling and must be removed every 500 hours for an inspection. Since the magneto probably won't make it to 1,000 hours you might as well do a complete 500 hour service to the magneto while it is removed for the coupling AD.

Later TSIO 360 engines came with a magneto pressurization kit on them with Slick or Bendix magnetos. Pressurization suppresses high altitude misfires (arcing) in the magneto when flying above 15,000 feet. A Bendix magneto will cost $300 to $500 for 500 hour service if the coil is not cracked (they are prone to this problem). The impulse coupling should pass two, maybe three inspections before needing replacement. Budget for $150 for a coupling.

The Slick magneto is not as robust as the Bendix magneto and for reliability 500 hour service must be accomplished on schedule. I have seen new Slick magnetos fail with less than 500 hours! The Slick magneto will cost $300 to $400 for 500 hour service. It rarely needs a coupling and has no AD against it. An after-market intercooler or an extra alternator and intercooler on the -MB engine adds to the difficulty of working on the magneto. Plan 5 to10 hours for the R&R.

Don’t cut corners with the magnetos. They keep your engine making horsepower and your propeller turning.

Vacuum Pump: A new dry-vacuum pump is a very reliable part, but it should be replaced every 800 hours if you fly IFR or if your autopilot operates using vacuum. Never use a rebuilt pump or install a rebuilt pump as these are not reliable and may not last even 100 hours. After a pump failure, always remove and blow out the line from the firewall to the pump as it may be contaminated from debris which will be sucked into your brand new vacuum pump when you start the engine. There are now a couple of manufacturers of new vacuum pumps which will cost $300 to $500, plus installation.

Push Rod Tubes: The last item on the TSIO-360 series that can be a nuisance is the push rod tube seal. The push rod tubes are located beneath the cylinders and run between the crankcase and the cylinder head. There is a seal at each end. As the engine heats up, it expands and the push rod tubes must be able to keep the seal as oil drains back through them from the cylinder head. A gap in the seal results in messy oil leaks. Each tube has a seal at each end and a spring on the tube keeps the seals seated on the case and cylinder head. The cylinder head seal is an o-ring that rarely leaks, but the case seal is another story. Some TSIO-360 engines I service never leak at the push rod tubes but others leak fairly often. TCM puts Dow Corning DC-4 on the seals and installs a new spring when they rebuild an engine. This sometimes works. There is no oil pressure at these points so it not a serious leak that needs fixing right away, but having a messy engine is annoying.

Flight operations for Engine Reliability:Most injected engines are set too rich at idle. After start, adjust the mixture for smooth idling. Just be sure to enrichen the mixture for runup and takeoff. During takeoff, smoothly advance the power to about 5” below maximum takeoff (TO) manifold pressure. After a few seconds the engine will stabilize. With the aircraft rolling continue the smooth throttle advancement to maximum TO manifold pressure. Too rapid throttle advancement on the -GB or -LB engine will cause over-boosting. Adjust the mixture for about 1400° TIT. Fuel flow should be 22 to 24 GPH. Initially climb about 110 IAS, then enroute climb at 120 - 130 IAS. Keep the engine at 2700 RPM, maximum TO manifold pressure and mixture set for 1400° TIT (22 – 24 GPH) all during the climb. Of course, once at or above critical altitude, the maximum attainable manifold pressure will require full throttle. For the 231, cowl flaps open. For the 252, close the cowl flaps slightly during cruise climb. If CHT is getting too high, increase speed (252, option - open cowl flaps more). It's best to keep the CHT needle away from maximum (460°) even if you lose some climb performance by going faster. Use 410° as a target maximum. In the summertime, high OAT may necessitate reducing manifold pressure to keep CHT under control. Consider using cruise-climb power settings (see POH performance charts) to assist in temperature control. The cylinder life you save, may be your own.

Once at altitude, let the aircraft accelerate before adjusting power. Make all adjustments to the engine slowly and smoothly. Reduce the power to slightly above the desired manifold pressure and then set the desired RPM. Close the cowl flaps. Adjust the mixture control. In cruise, the TIT should be kept no higher than around 1600˚. The airspeed should be stabilized by now. Readjust the manifold pressure as it changed when the RPM and mixture changed. After a few minutes for stabilization, check (and adjust if necessary) RPM, manifold pressure and mixture (fuel flow/TIT). The CHT should be 375˚ to 410˚ in cruise and oil temperature 180° to 205°. It may be difficult to maintain these numbers when the OAT is much above standard day, especially above 15,000 MSL (231) or FL210 (252). This is due to the reduced efficiency of the engine caused by having to greatly compress intake air to maintain required horsepower. That reduced efficiency means that more heat is being produced at high altitudes to obtain a given IAS, i.e. cooling air. On the 252, cowl flaps may be opened partially to help cool the engine. On the 231, try the TRAIL setting; full OPEN may cause too much drag. On either model, reducing power may be the best option. In cruise, higher rpm (e.g. 2600 vs. 2500) and higher horsepower (e.g. 75% vs. 65%) shortens cylinder life, it’s just that simple. Unfortunately, at higher altitudes, higher RPMs are needed to develop higher power output. Think of the engine as an air pump to supply high pressure exhaust “air” to drive the turbocharger exhaust turbine. Of course, the huge trade-off for going up is higher TAS and, with luck, significant tailwinds..

What are good EGT numbers to use? Neither TCM nor Lycoming publish EGT numbers for their turbocharged engines, so this number is anyone’s best guess. Both manufacturers use TIT numbers and only provide never-exceed numbers, not reliability numbers. For turbocharged engines, use TIT and disregard EGT. Use individual cylinder EGT to troubleshoot erratic running engines.

So far, for piloted vehicles, what goes up must come down. Proper engine operation during descent can go a long way toward good engine health. Two basic rules: keep the engine warm (avoid shock cooling) and keep the propeller pulling (positive torque). If you have the luxury of a long gradual descent, plan for 500 fpm and an increased IAS. If under ATC positive control, coordinate with ATC (request a descent a few minutes early). Adjust for wind and turbulence. The ideal is to remain at near cruise power and use the descent to increase speed. Once started down, if applicable, fully close cowl flaps. Don't allow the manifold pressure to increase. As you descend and once in warmer air, gradually reduce the manifold pressure. A good target is about 20” by pattern/initial approach altitude. At no time (except an emergency), reduce power below 15” until final descent to land. Instrument approaches often require engine power changes, so have the engine temperatures a bit lower than peak to avoid cooling stress when ATC requests an expedited descent and/or slow-down. Gear down at 150 IAS helps to avoid pulling the power back too far. If your aircraft has speed brakes installed, you have an excellent tool (in lieu of the landing gear) to allow power to be kept on the engine and still descend rapidly, at any altitude. Once on the ground and clear of the runway, remember earlier that the idle mixture may be too rich – adjust the mixture control accordingly. Start the clock on providing engine and turbocharger cooling down time. That cooling time will also allow for turbocharger oil scavenging.

Current Outlook: When the M20K was new, these engines were very affordable and leak free. But it you evaluate , for instance, a 1986 252, now 25 years old with an engine that has been overhauled and/or has overhauled parts in it, that affordability has been compromised

When Superior Air Parts was in business, TCM had some competition for part prices. That competition kept prices down. With Superior Air Parts bankrupt for the last three years, the parts inventories have dried up. TCM is now the only game in town for parts like T-drive gears and turbocharger check valves; they can charge whatever they want. Combine this with a shrinking marketplace, fewer pilots and aircraft owners; soon you will find parts are not available out of stock but are being made to order.

This method of making parts piecemeal is very expensive and the affordability equation is badly skewed. The engine overhaul shops are also being squeezed because they are competing with the TCM factory for sales. To offer new parts they must buy from TCM; not all shops can do this and those that can operate with narrow markup. This is why they put overhauled gears in your engine instead of new parts. No scam here; an ethical shop will discuss all available options with you, up front.

Ten years ago I wrote an article for MAPA about engine overhauls and at that time overhauled cylinder assemblies were the parts to be wary of, but now every part in your vintage engine is potentially overhauled. Some parts have been overhauled so many times that they are just no good anymore and have no reliability (such as T-drives). So what is an owner to do when it's engine overhaul time? The surest way to get back the reliability of your 25 or 30 year-old engine is to dump it and buy a new one.

Most of us just can’t afford this option so the next step is a factory re-manufactured engine. Ten years ago, I would not have recommended this but today's reality is that these parts and these accessories have been in service too long and overhauled too many times, it’s not just about cylinder assemblies any more. Don’t get me wrong, there are some good engine overhaul shops in the US. But, to get an engine with new parts in it instead of overhauled parts you’ll probably have to go with the TCM factory for the best price, and that’s the sad truth.

As always, if you have any questions about this article, feel free to contact me at 307-789-6866 or via e-mail. And if you’re running an engine shop and trying to make a living, I won't be surprised if you call and scream at me. I’m just trying to tell it like it is, please don't shoot the messenger. Until the next ShopTalk, enjoy flying your Mooney.

KNR-e-mail