Reviving an inactive engine
"OK, Christmas is over, I survived the launch of another new year, and I'm ready to get back in the air. It's been a long winter and I haven't logged one hour since that last big storm in mid-December."
"Gosh, the avionics installation and instrument-panel rebuild took a lot longer than we thought. It's been three and a half months since the propeller has turned."
"Oh boy, I finally got the seller to come down to my price. We've been locked in this bidding struggle for four months — and I'm rarin' to fly my new bird."
These three stories pose different versions of the same problem. Do engines need special attention after being inactive? What if the period of inactivity is less than a month? If engines deteriorate during inactivity, what's the best way to lessen the damage? What should I do before the first flight after the airplane has been sitting for a while? Let's look at some answers to these and other questions about returning an aircraft engine to service.
Inactivity, or merely a short rest?
Airplane engines thrive with use. Commercial operators have proven that long hours of daily flying won't hurt an engine — provided that regular inspections and preventive maintenance are administered (see " Airframe and Powerplant: Fleet Fliers Run Rich — With Good Results," August 2002 Pilot).
Yet many owners complain about their engines. Dive into any online engine chat room and you'll see comments like this one: "I have owned my first airplane for three years. I don't fly it a lot, but it seems to be very expensive to maintain." The difference in satisfaction between the fleet flier and the private flier is based on how often they fly their airplanes. And the reason that frequency of flight is so important is because of one thing — moisture.
Rust, corrosion, oxidation — they're all stripes of the same cat. To stave off the effects of moisture, pilots must fly often enough to raise the temperature of the engine and oil to levels that cause the moisture to evaporate.
Right now let's look at what the two major engine manufacturers — Continental and Lycoming — say about periods of engine inactivity. Common terms for inactivity are flyable storage, temporary storage, and indefinite storage.
Flyable storage
Lycoming Service Letter L180A is titled "Engine preservation for active and stored aircraft." This letter says that the maximum limit of inactivity is 30 days — if there has been no activity in 30 days then the engine should be flown for at least 30 minutes. The two-page Lycoming letter is short and to the point.
Continental Service Bulletin M91-5, which is also titled "Engine preservation for active and stored aircraft," covers five pages. This bulletin says, "The best method of preventing corrosion of the cylinders and other internal parts of the engine is to fly the aircraft at least once a week."
Continental's flyable storage plan is split into two parts. The first part applies to engines with 50 or fewer operating hours (Continental calls this Program I) since overhaul or since one or more cylinders have been changed. These engines should be flown every 15 days. Engines with more than 50 operating hours (Program II) should be flown every 30 days for at least an hour. The more frequent action for Program I engines is because new engines (and cylinders) are particularly susceptible to rust. The semiprotective varnishlike coating that slowly builds up inside gasoline-fueled internal combustion engines hasn't had time to form.
Both Lycoming and Continental written service information recommends that owners pull the prop through by hand — every five days for Program I engines and every seven days for Program II engines. In the years since the bulletins were written (M91-5 was written in March 1991, and L180A was written in December 1978) virtually all engine experts have come to the conclusion that pulling a propeller through by hand during nonoperational periods creates more problems than it solves. Current thought holds that if the engine is inactive, you shouldn't do anything until the next flight.
Most emphatically, all engine experts agree that ground running, which is also mentioned in the manufacturers' bulletins, is very bad for inactive (nonflying) engines. Ground running results in uneven (or nonexistent) cylinder cooling and very rarely raises the engine oil temperature enough for the moisture evaporation process to take place. In addition, most ground running is done at extremely rich fuel-air mixtures. These rich mixtures dilute the engine lubricating oil and contribute to the formation of metal-eating acids that are then circulated throughout the engine in the oil. The experts now say to fly it or leave it alone.
The written service information says that the engine is probably OK if it sits for 30 days. Engine shop experts tell a different story, especially concerning newly rebuilt engines or cylinders.
Bill Middlebrook of Penn Yan Aero Services in Penn Yan, New York, builds up new engines with rust-inhibiting preservatives and won't put an engine through a test-cell acceptance run until shortly before its shipping date. "If we run a brand-new engine for an hour, we've introduced acids and moisture to that engine," says Middlebrook.
Cylinder-wall rust is a big enough concern that Continental started covering the walls of new cylinders with a manganese phosphate coating immediately after the cylinder walls are ground to a ring finish. This protective coating wears off during the first 20 to 30 hours of use.
Temporary storage
The Lycoming bulletin doesn't address temporary storage. It says that inactive storage applies to periods longer than 00 days and requires a full engine preservation procedure. More on this later.
The Continental bulletin designates periods from 30 days to 90 days as temporary storage. If the engine is going to be inactive longer than 90 days, then indefinite storage procedures are spelled out.
Continental's plan for temporary storage involves protecting the cylinder bores from rust by removing a spark plug and spraying a liquid preservative in each cylinder. Preservative is also sprayed down the oil filler port. Each engine opening, such as the exhaust pipe, breather tube, and oil filler port, is sealed with tape, and the spark plugs are reinstalled.
The Lycoming plan for inactive storage and the Continental plan for indefinite storage are very similar. In addition to the procedures detailed above for cylinder preservation, each engine is flown with preservative oil (Shell Aeroshell 2F is specified by Continental, while Lycoming recommends one part of MIL-C-6529C type I concentrated corrosion-preventive oil to three parts of mineral oil) in place of normal lubricating oil.
Then the engine is sealed up, only this time small bags of moisture-absorbing desiccant material and special desiccant spark plugs are installed before the final sealing. These materials are available from aircraft supply houses such as Aircraft Spruce and Specialty ( www.aircraftspruce.com) and Chief Aircraft ( www.chiefaircraft.com). Tanis Aircraft ( www.tanair.com) sells engine preservation kits that include all the products needed to follow both the Lycoming and Continental procedures. The kits also include copies of the appropriate service information.
For most of us, thoughts about preserving an engine get lost in the shuffle of getting home and hearth ready for winter, or planning an avionics installation. Whatever the reason, airplanes invariably sit for 30 days or more. When we're finally ready to fly, we hope to fly a lot without any maintenance upsets. If you have preserved your engine, remove all the seals and any preservative 'araphernalia, and give it a good once-over. Here's what I did to the 2001 AOPA Sweepstakes Bonanza's sleeping engine after idle periods.
Clean oil
I completely removed the cowling and inspected for bird nests and any obvious damage. Birds think the top of an inactive engine is a fine place to build a nest.
I drained the oil and took off the oil filter. I cut open the filter and checked for contamination. It didn't matter that the oil only had 17 hours. What was important was that the engine had been inactive, and the recommended four-month oil change interval had passed. Changing the oil was the only sure way to remove the accumulated acids and moisture before I started the engine.
While I had the spark plugs out for cleaning, gapping, and testing as part of the annual, I pre-oiled the engine by charging the airplane battery and spinning the engine with the starter until I got an oil pressure indication on the cockpit pressure gauge.
I also cleaned the outer surface of the battery, shined the battery connection and terminals with a stainless-steel wire brush, and charged the battery. The correct way to charge aircraft batteries is to trickle-charge them at a rate that is no greater than 4 amps. It may take up to eight hours to get a full charge at this slow rate.
Fuel system water
I drained at least a quart of fuel from each fuel sump. This is an especially important step for airplanes that have been parked outside. Fuel caps leak. If your airplane has been tied down outside during inclement weather, I'd take extra steps, such as a rock 'n roll-style preflight, to make sure that every bit of water gets to the sumps.
This process varies with each airplane but generally consists of doing all that's physically possible to ensure that any water in the fuel system can flow to the sump area of the tank. Airworthiness Directive 84-10-01, which addresses water issues in the bladder-type fuel tanks of various Cessna airplanes, requires the owner to lower the tail to within five inches of the ground and then move a wing tip up 10 inches and down 10 inches 12 times (hence the name rock 'n roll) any time the airplane is exposed to "rain, sleet, snow, or after fueling from an unfiltered source."
This procedure works for Cessnas because of the flexibility of their spring-steel landing gear, but it won't work on most other airplane models. Since most fuel-tank sump drains are at the aft inboard location of the tanks, airplanes with tricycle landing gear move water toward the sumps when the owner lowers the tail to the ground while a helper rock 'n rolls the wings. Since airframe damage can occur if this isn't done right, ask your mechanic to show you the correct way. Continue with these procedures until three or four (or five) sump samples are free of water.
The first flight — take it easy
The first flight after an extended period of pilot and airplane inactivity, or the first flight after any maintenance procedure involving engine repairs or major repairs or alterations, should always be undertaken with a Harry Trumanlike personal attitude. (A sign on President Truman's desk read, "The buck stops here.") Don't assume that the mechanic took care of everything. In other words, this flight requires the pilot to take control of, and responsibility for, doing a thorough preflight and assuring that every factor that might affect the safety of the flight is checked and determined to be safe.
If the fuel tanks are partially full, Take sure there's enough fuel for a safe flight with plenty of reserves. Cycle fuel selector valves through all positions, checking for distinct detents and smoothness of motion.
Manually test the control surfaces for travel and freedom of movement without any binding or unusual noises. The nests of opportunistic birds can bind up controls. Inspect the inlet air filter. Inspect the main fuel filter — if there's any evidence of contamination or blockage inspect the carburetor or fuel-injection finger screen.
Pick a day with good enough weather that you aren't concerned with low ceilings or gnarly crosswinds. The purpose of the first flight is to responsibly return yourself and your airplane to the sky. Devote a whole day to this process if you're going to do it yourself. (Owners are allowed to do all the listed procedures under the FAA definition of preventive maintenance.) The point is to ensure that the pressure of a ticking clock doesn't short-circuit the steps required to safely return to flying. Use a preflight checklist and check every item — perhaps both the pilot and the airplane have been out of service for a while. This slow and thorough approach also applies after the engine is started. Do a thorough runup and work through the pretakeoff checklist. Ask the tower to confirm that your radios are (both) providing loud and clear communications. If the tower asks you to expedite your takeoff because of traffic on short final, tell them you'll wait. You don't want to put yourself in a position where you can't abort the takeoff if everything isn't perfect.
During takeoff apply throttle gradually and check the engine gauges. Monitor the fuel flow gauge to make sure that fuel-injected engines are getting full fuel flow. Climb out gradually and spend the first 15 minutes within gliding distance of the airport. If everything looks good, feels good, and smells good at the end of 15 minutes, set a course for your first $100 hamburger of 2003.
E-mail the author at [email protected].
