Airframe and Powerplant

Learning Your Lycoming

May 1, 2001

'I've been doing it wrong for 24 years — and now I know why!'

Outside it was a typical January day in Williamsport, Pennsylvania — gray, mid-30s, and spitting snow. Inside the warm, new classroom at the Pennsylvania College of Technology Aviation Center, 12 men introduced themselves and settled in. They were the members of the January 29 Lycoming engine service school class. As a group they would spend four days together learning about Lycoming engines. They were a mixed group — four were employed by various aviation companies, three were retired, one was a teacher in an aviation high school, one leased airplanes, one worked for the FAA, and one claimed to be completely nonmechanical, just a pilot who loved flying his Citabria and wanted to learn more about his trusty Lycoming engine.

Instructor Jim Doebler told the class right off what the purpose of the course was: "Basically, what we're going to do in the next few days is build this engine up in theory."

After teaching a little Lycoming history (the company moved from making the Demerest sewing machine to bicycles in the 1890s; it wasn't until 1938, with the 55-horsepower O-145, that its first light-airplane engine was built), Doebler smoothly worked his way through the parts, pieces, and operation of Lycoming engines. He covered crankshafts, camshafts, valve trains, nitriding and carborizing, and the difference between a wide-deck and a narrow-deck engine. Doebler boiled down these nuts-and-bolts subjects until everyone understood them. Probably the most important lesson the more experienced members of the group learned was how Lycoming communicates with users through its publications to keep everyone abreast of all its company, industry, and product changes.

The classroom would fill with the flutter of flipping pages as the 12 men (no women had enrolled in this class) turned page after page, gathering information from Lycoming service letters, service instructions, and service bulletins.

One thing that soon became obvious was that anyone working on a Lycoming engine with only an overhaul manual would be way out of the critical information loop — all the critical information, including changes in torque values and parts upgrades, is in the latest service publications. This conclusion was further reinforced when Doebler acknowledged that the direct-drive engine overhaul manual hadn't been revised since 1974.

After three and a half days of flipping pages and passing around various engine hardware (camshafts, connecting rods, pistons, valves, and the like), the gang grouped up and caravaned seven miles into Williamsport for a tour of the Textron Lycoming reciprocating engine factory. A couple of hours later the class members started drifting toward home. Another week, and 12 more airplane people, from places such as Spokane, Washington; Sturgis, North Dakota; New York City; and Everett, Washington, would know where to find the latest information on their Lycoming engines.

Everyone received a certificate of completion (it's impossible to fail unless you can't complete all 28 hours), a shiny new Lycoming coffee cup, and a complete set of service letters, bulletins, and instructions, plus a year's subscription to the updates. Since the flying weather was pretty crummy over most of the country that week, everyone agreed that the school was not only a good place to get through another week of winter, but had turned out to be worth the trip for anyone wanting to know more about Lycoming engines. As one experienced airframe and powerplant mechanic said, "I learned that I've been doing it wrong for 24 years — and now I know why!"

Textron Lycoming service schools

The school day really started around 7 a.m. as most of the class met in the motel breakfast room (Lycoming has arranged for a good rate at the local Holiday Inn) over coffee, bagels, juice, and cereal to get better acquainted and share airplane stories. The service school will hold 16 sessions this year. There's also a disassembly and reassembly course, but it's only offered a few times each year. More class information can be obtained on the Web site ( or by telephoning 570/327-4775 or faxing 570/321-5546.

Classroom work starts at 8 a.m. on Monday and goes each day until 4 p.m., with an hour for lunch. During the Thursday-afternoon Lycoming factory tour, Doebler led everyone through the old building to stations where they watched the experts tear down, inspect, repair, and rebuild customers' engines. This factory also remanufactures cores that have been exchanged for factory remanufactured engines, and assembles new engines. Each engine is shuttled through one of the test cells and run for at least one hour before it's moved onto the trim line and readied for shipping.

The book

In the classroom, each two-man desk held an upright book of Textron Lycoming service bulletins, service letters, and service instructions. A good percentage of the class time would be spent thumbing through these books to dig out the latest factory information on topics such as silk thread, approved engine case halve sealers, new torque values, and before-torque lubricants. So what is the difference between a service letter, a service instruction, and a service bulletin?

A service letter is printed in black and does three things. It can announce new products. For instance, Service Letter L114AJ (January 15, 1999) announced the latest editions of reciprocating engine and accessory maintenance publications. A service letter can also announce a change in Lycoming company policy — Service Letter L220B (November 4, 1998) is titled "Non-Availability of New Standard Cylinder Flange Engines." This letter announces that standard (narrow deck) cylinders for O-235 series engines are no longer being made and will be replaced by a wide-deck version of the same cylinders. A service letter can also provide a way to notify the industry of more mundane subjects, such as a telephone area code change (Service Letter L237, December 30, 1998).

Service instructions are also printed in black and tell how to perform a change or operation. Service Instruction 1489 (November 20, 1998) announced that a 4-psi fuel manifold (spider) spring change is recommended for all IO-360-L2A engines up through serial number L-27982-51A installed on the new Cessna 172R aircraft. The time of compliance is at the owner's discretion when rough idling occurs. Service Instruction 1492A (December 30, 1998) is titled "Piston Pin Plug Wear Inspection" and suggests methods of detecting abnormal piston pin plug wear.

Service bulletins

Service bulletins are printed in red and address safety of flight issues. An example would be Service Bulletin 480B (June 29, 1998), which is an update on an earlier service bulletin related to oil and filter changes and cleaning. A sentence has been added that says that an oil change and filter replacement is recommended at 50-hour intervals for all engines using a full-flow filtration system (except for TIO-540-AF1A and -AF1B engines used on Mooney TLS M20M models; 25-hour intervals are recommended for these engines). With the exception of the Mooney M20M information there's nothing especially new there for most Lycoming engine users, yet a sentence at the bottom of the page reveals hard-to-find and vital service information. It says: "All turbocharged engines must be broken in and operated with ashless dispersant oil." The reason for this is that straight mineral oil, which is generally the break-in oil of choice, is likely to carborize or coke up because of the extremely high temperatures at the center bearing of a turbocharger (or turbonormalizer). Because of this coking tendency, only ashless dispersant oil (sometimes called compounded or detergent, although these terms aren't correct) should be used in turbocharged or turbonormalized engines.

One of the most important reasons for obtaining a service information subscription is because it's the only way owners can get maintenance information that has a bearing on the correct operation of their airplanes. Since Lycoming didn't print engine maintenance manuals until it introduced the 580 series, there's simply no other place to obtain the latest factory data on maintaining these valuable engines.

Is a private aircraft owner required to comply with service bulletins that arrive periodically from Lycoming (and other manufacturers)? It would seem so, especially since the word mandatory is printed in bright red letters at the top of Lycoming's bulletins. But the answer is no. There is no regulatory requirement that private airplane owners (operating under Part 91) comply with these bulletins. That doesn't mean they should be ignored, however.

LW-16702 oil additive

Occasionally a service bulletin will update a service instruction, especially if it seems that users are missing the message. This happened in early 1999 with the issuance of Service Bulletin 471A. This bulletin relates to the use of Lycoming antiscuffing additive LW-16702 in the oil of TIO-541 and TIGO-541 engines that are most commonly installed on Beech Dukes, pressurized Beech Barons, and pressurized Piper Navajos. The language in the service bulletin, with words such as must and essential, is unmistakable — use this additive at every oil change or suffer the consequences. Again, with current data available only from service bulletins, letters, and instructions, this vital information would be missed without the subscription.

Service Instruction 1409B also mentions LW-16702. If owners and/or their mechanics haven't read this instruction, they won't know that Lycoming recommends that this antiscuffing additive be added to all of its engines (except for a few that are equipped with a friction-type clutch) at every oil change. It helps lubricate the camshaft and hydraulic lifter bodies after engine startup before the oil has completely circulated. If owners are using oils that have this additive (Aeroshell W100 Plus and 15W-50 multigrade oils, and Exxon Aviation Oil Elite 20W-50) then they should not add the LW-16702 to their oil.

Neat to know

Jim Doebler offered hints gleaned from years in the Lycoming engine business. This type of "insider" information is hard to get. According to Doebler, engines equipped with pressure screens (instead of filters) are designed so that the solder joint in the pressure screen acts as the screen bypass should the screen become plugged with metal or carbon. The following are just a few Doeblerisms that popped out during class:

  • "About one-third of the engines that come down the overhaul line have to have new camshafts."
  • "A healthy Lycoming engine will have a 10-to-12-psi difference between the oil pressure readings at the left front of the engine and the right rear of the engine, with the right rear readings being higher."
  • "Props are not indexed [mounted to the crankshaft] with hand-propping in mind."
  • "Exhaust gases are like people — they like to take the path of least resistance."

After-school help

Tony Royal, one of the class members, brought the bottom end (sans cylinders) of his IO-360 engine with him. He was planning to rebuild it himself since the camshaft had quickly worn after the last field overhaul. But he just didn't know how to get the two case halves apart. So after school on Wednesday night the class gathered in the school engine shop (there's an active A&P school on site) and got a hands-on lesson on case splitting.

"No problem," said Doebler as he disappeared into another room. In a moment he was back with a large slide hammer. Splitting the case involved no more than applying a few healthy whacks to various cylinder hold-down studs he had screwed the hammer onto. Within 10 minutes the crankshaft, the camshaft, and the two case halves were lying on the workbench. Unfortunately, one lobe of the camshaft was badly worn and two hydraulic lifter bodies were spalled. After watching theory and application meld together before their very eyes, a few members of the group asked about signing up for the disassembly/reassembly classes.

Disassembly and reassembly classes

Unfortunately there are only three disassembly/reassembly classes scheduled for 2001. And they're already full. It's too bad because the two classes seem to complement each other. Perhaps Lycoming will see the need for more of these classes and add some to the schedule in coming years.

Although the service school costs $500, a portion of this cost is offset because each class member gets $125 worth of bulletins, letters, instructions, and updates. To further help out, a bound copy of Lycoming Flyer key reprints, a couple of special service publications covering engine-mounted oil filter kits, and a reciprocating engine troubleshooting guide were also included. If you'd like to take a look at this troubleshooting guide and other Lycoming printed information, visit the Web site (

For years Lycoming used to print and mail out a newsletter titled the Lycoming Flyer. Eventually the editor retired. Instead of starting the Flyer back up, Lycoming elected to bind and print what they call key reprints from the newsletter. Lycoming gives boxes and boxes of these reprints away at airshows.

It's often been said that not to know is bad, but to not wish to know is worse. For those who want to know all they can about their Lycoming engines, the service school is a great way to get started. Everyone in the February 29 class of 2001 seemed to go away impressed. If you're too busy to make it to a class this year, or want to keep up to date on your Lycoming engine without going to school, a complete set of service bulletins, letters, and instructions can be purchased by contacting Textron Lycoming at 652 Oliver Street, Williamsport, Pennsylvania 17701; telephone 570/323-6181; or visit the Lycoming (the locals call it Ly- come-ing) Web site (

E-mail the author at [email protected].