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LYCOMING ENGINE OVERHAUL CONSIDERATIONS
ShopTalk - July 1999


I would like to take this opportunity to share some of my experiences with overhauled aircraft engines and how the overhaul industry has changed over the past twenty years. I will discuss the Lycoming 0-360, IO-360, and TIO-540 engines in this article. In my next article, I will discuss TCM TSIO-360, TSIO520, and IO-550 engines.


Let's begin by discussing what your options are when TBO arrives. Almost everyone first thinks of replacing their worn out engine with a factory-new one. Both factories (Lycoming and Continental) offer new engines and these are exactly that - new. These engines are built with all newly manufactured parts and have zero time, but they are expensive and are not without their faults.


I can give you a good example of how buying a new engine resulted in unexpected headaches. In January 1997, the FAA issued airworthiness directive #97-01-03 requiring replacement of piston pins in TIO-540 engines manufactured within a certain time frame. If you bought a new TLS or a new engine or a new cylinder assembly for it, you may have had to disassemble your new engine to comply with the AD.


The next consideration for replacing your run-out engine is a factory remanufactured engine. These engines may have been remanufactured using crankshafts, crankcases, and drive gears all within new limits, but not necessarily new parts. The rest of the parts in these engines will be new. These engines are considered "zero timed", but only the engine manufacturer can make this statement.


Next offered by the factories is a factory overhaul. It's almost the same as a factory reman, except the new logbook has the total time of that engine they overhauled that you must carry forward in the engine logbook.


The last options are 1) a rebuilt engine by an authorized aircraft engine overhaul shop or 2) an engine overhauled by an FAA powerplant-rated mechanic. These two options vary widely as to what new or used parts may be in them and if these parts meet new or serviceable limits when installed in that engine. Serviceable limits mean the part in question was serviceable only when installed. However, keep in mind that the part could be worn out within one hour of running the engine. The FAA considers any part within serviceable limits to meet overhaul requirements. As you can see, you must be careful when shopping for an engine replacement.


Another item to consider is the resale value of your new engine. If you buy a factory-new, reman, or overhaul, just about everyone agrees that you got one of the best since you went directly to the people who manufacture them. But some nationally recognized engine overhaul shops also provide good resale value if and when you decide to sell your airplane. On the other hand, it is rare to find an FAA powerplant mechanic that is recognized in the field for overhauls. Even though you can get some excellent overhauls done by experienced and knowledgeable powerplant mechanics, this option rarely provides any type of resale value.


On Lycoming engines, I always insist on all new cylinders including pistons, valves, valve springs, valve guides, valve keepers, and valve rotators. Twenty years ago (1980s) it was a different story concerning cylinders. There were a few cylinder options, such as exchange overhaul, channel chrome, and rebarreled cylinders. More cylinder options have been added in the last ten years like cermichrome, satin chrome, new chrome, boring oversize, new Superior cylinders, and cerminil. Even though some of these options work well, you often cannot determine how many times any cylinder has been overhauled or welded and overhauled. Every time the aluminum head on the cylinder assembly goes through another cycle (heat-up and cool-down), it's just one more cycle closer to cracking. Since no one records the total time on cylinders, you may get a first-overhaul or a seventh-overhaul cylinder.


Another problem with overhauled cylinders is if the overhauler grinds and seats the valves instead of replacing them. If ground and seated, the rocker arm ratio changes, causing stress on the camshaft. If the crankcases are lapped and line-bored, this places the rocker arm pivots closer to the camshaft, reducing dry valve tappet clearances. Lycoming engines have different length pushrods so you can maintain the correct valve clearances, but they also have a camshaft mounted high in the crankcase that sees very little oil during start-up and tends to wear down the cam lobes pre-maturely.


A classic example of Lycoming camshaft wear is a customer who can't believe how much faster his IO-360 powered M20J 201 is after installing a new engine. He also cannot understand why his airplane just sails along at 12000 feet when the last engine would barely get him there. It is a simple fact that a new (unworn) camshaft is allowing the valves to open farther and stay open longer. The engine is therefore developing its correct rated power.


Most people think that compression is what makes horsepower and torque in an engine, but camshaft duration and lift are what allows the engine to breathe properly. If your engine can't breathe, compression means nothing. Always get a new camshaft. Reground camshafts are okay in your car but camshaft data (ramp and lobe lift) are proprietary info that Lycoming does not give out. This makes it difficult for a regrinder to get the job perfect every time.


Many parts are mandatory replacement items during overhaul as per the Lycoming direct drive overhaul manual. Some other parts just make common sense to replace. Items such as rod bolts, gaskets, oil seals, oil pump gears, main and rod bearing, needle bearings, hydraulic lifters, oil pump drive gear shaft, rod bolt cotter pins, all safety wire, all bushings, spark plugs, fuel injection nozzles, alternator belt, and oil filter should be changed. Drive gears and some hardware can be reused if they are magnafluxed for cracks and inspected for wear and pitting. Rods can be resized and rebushed. Counterweights can be rebushed and reused but pins and clips must be replaced.


In the accessory department, I always insist on new Slick magnetos and harness. Bendix mags are okay to be rebuilt. The fuel servo and flow divider or the carburetor must be rebuilt or replaced. Always install a new fuel pump (gear driven pumps can be rebuilt). Prop governors are getting like rebuilt cylinders, so make sure the flyweight assembly in your overhauled prop governor is new if you cannot verify the total time on it. A new permanent magnet starter is worth every penny on Lycoming engines (not Continental engines) - this is a good opportunity to get rid of your old field coil type starter.


You can overhaul the alternator but always buy a new dry air vacuum pump. Wet pumps can be overhauled. Don't waste your time on dry vacuum pump kits. They don't last very long and your vacuum pump is pretty important in IMC conditions. Always have your oil cooler flushed out and at least resealed (or overhauled) before installing it on the engine. Don't allow any of the old oil from the hoses, oil cooler, or prop to get into your new engine. At engine replacement time you should replace all fuel and oil hoses and install fire sleeve on the new hoses before installing them in the engine compartment.


I'm going to take a moment to talk about porting and flow balancing cylinders and balancing the engine. Some rebuilders want you to believe these things will make your engine better. Flow matching or balancing cylinders won't hurt, but don't let anyone remove any material from your cylinders so they will all flow the same amount of air. When an automotive race engine is ported, it requires the removal of cylinder head material in an attempt to allow air to flow in and out of the intake and exhaust ports. This practice creates an engine that will rev higher and faster, but aircraft engines don't run faster than 2700 or 2800 RPM and are operated typically at a constant 2400 RPM for long periods of time. Porting is a waste of money and will only cause premature cracked cylinders and worn-out valve guides.


Balancing an airplane engine is a good thing if done properly. The problem is that to balance a rod properly, you must first balance each end of the rod and then mass balance that rod to match the others. Most shops won't take the time to do it right. Your crankshaft will already be balanced when overhauled and your overhauler can install balanced piston sets. Counterweights are always matched and installed as pairs so they will be okay. Try to remember that we are dealing with an engine that turns only 2700 RPM- not 7000 RPM like an automotive race engine. You can do more good by dynamic balancing your prop and engine at normal cruising RPM after the engine is broken in.


Oil is one of the most misunderstood options an aircraft owner must deal with, but it's one of the most important items you must understand if you want your engine to get to TBO. Aircraft engines were designed long before synthetic or semi-synthetic oils. Let's take a look at what works and what is a waste of money. As I said before, airplane engines run at a constant RPM for the majority of the time, so you need an oil that won't change viscosity and will maintain good flow through the engine at 200 degrees oil temperature. This is a job for straight-weight ashless dispersant (think detergent) oil, not a multi-viscosity oil. Your car is operated in a variable RPM range and has much tighter tolerances than your airplane engine. Your car can use a multi-viscosity oil. Your airplane usually doesn't need it.


The only reason to run multi-viscosity oil in your airplane is for cold-weather starting (below freezing). Here in Wyoming, I service my customers with Aeroshell 100W in the summer and Aeroshell 15/50 in the winter. IF you live in the southeast or southwest, you can use Aeroshell 100W in the summer and 8OW in the winter, assuming you don't live where it snows. And don't mix brands of oil - if you prefer Phillips oil, stay with it.


On the Lycoming IO-360 engine and TIO-540, I recommend changing the oil at 25 hours. As the oil starts to get black or dirty, its viscosity gets thinner and the engine will tend to use oil faster. By keeping clean oil in the engine, it will tend to use less of it, and provide better lubrication because the viscosity remains close to the original weight. Dirty oil also loses its ability to carry contaminants to the filter. Just because one quart of oil is five dollars and another is only two dollars doesn't always mean the five-dollar oil is better.


During engine overhaul time, the flame tubes in your muffler, and the ball sockets in the exhaust systems should be inspected and overhauled as necessary. Turbo models should always get new V-band clamps if the time on the clamps cannot be verified. V-band clamps are very important. If they are old, throw them away and put new ones on. Remember that a little preventive maintenance now will give you more quality flying time later and some of these items are just a drop in the bucket compared to the cost of the engine overhaul.


I hope I have brought to light the dos and donts of Lycoming engine overhaul in your Mooney. In my next article, I will address the same for Continental engine overhauls. If you have questions about this or any other ShopTalk article, please e-mail me at shoptalk@knr-inc.com or call me at my aircraft repair shop, 307-789-6866. All ShopTalk articles can be read here at www.knr‑inc.com. Until next time, enjoy flying your Mooney.

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