Editor in Chief Tom Haines owns — and sometimes gets to fly — a 1972 Beechcraft A36 Bonanza.
Myths and old wives' tales abound in general aviation. In " Wx Watch: Proverbial Weather" on page 125, Editor at Large Tom Horne devotes several pages to weather lore. And there are operational folk tales: Never run the engine lean of peak or, before your very eyes, it will disintegrate into some steaming heap of molten steel and aluminum. Associate Editor Steve Ells put a bullet in that myth in " Airframe & Powerplant: Lean-of-Peak Lessons" (September Pilot).
Another subject rife with conflicting information is engine overhaul. If Billy Bob at Joe's Engine Shop tells you he can "zero time" your engine, run — fast — in the other direction while your wallet is still intact.
I've been involved in numerous engine overhaul decisions and even flown several airplanes with brand-new or just-overhauled engines in them. The type of engine overhaul is never an easy decision.
Last month I described in woeful detail how the engine in my airplane had turned itself into a bunch of expensive paperweights. No, seriously, the damaged tappets make great paperweights and conversation starters. The engine is back from overhaul now. Along with it came a box of damaged parts. One lobe on the camshaft is more than a quarter of an inch shallower than the others. The camshaft with its red tag will make a nice lamp stand.
I had my engine sent off to Penn Yan Aero Service for an overhaul to new limits. I could have had it overhauled to service limits. Other choices include a factory-new engine or a factory-rebuilt engine.
A factory-new engine is just that — brand-new never-seen-an-airplane parts throughout. For obvious reasons, it's the most expensive option and probably isn't necessary for most owners, unless you want to take advantage of some special deal from the manufacturer. Continental, for example, offers its Platinum series of new engines, which come from the factory with a number of enhancements, including balanced fuel injectors and other components and an extended warranty.
A factory-rebuilt engine is a less expensive option. A factory-rebuilt engine often runs down the same assembly line as new engines and includes many new parts. Every part will be to new limits, meaning any used parts will meet the same tolerance criteria as new parts. A factory-rebuilt engine also gets a new logbook, serial number, and dataplate, making it a "zero time" engine. Only the engine manufacturer can zero time an engine, thus the warning about Billy Bob's claims. A factory rebuild assures that you're essentially starting with a new engine, which brings a certain peace of mind and some additional value at resale — especially if the resale happens within the first few hundred hours of use.
The next option is an overhaul to new limits. In addition to new engines and factory rebuilds, Lycoming offers its customers a factory-overhaul option, which doesn't necessarily contain as many new parts as a factory rebuild — although it may. But a factory-overhauled engine doesn't come zero timed. Continental doesn't offer a factory-overhaul option, but Teledyne Mattituck Services, a subsidiary of the engine manufacturer, does overhauls. Mattituck's signature overhaul is the RedGold option, which includes a number of enhancements. Ironically, Mattituck, owned by Continental, is also one of the largest overhaulers of Lycoming engines.
Penn Yan is another large overhaul shop. On a typical day 35 to 40 engines will be in various stages of overhaul. It has its own test cell where each engine is run and tested before it's shipped for installation. That run in the test cell eases the burden somewhat on the aircraft owner because that critical first hour or so is run under highly controlled conditions.
Penn Yan's typical overhaul is to new limits. If you want new cylinders, it can provide them from a variety of sources — the factory, Superior Air Parts, Engine Components Inc., among others. Otherwise, you can elect to have your existing cylinders overhauled if they can be brought into tolerance.
The least expensive option is an overhaul to service limits. Usually this is one of those throwing-good-money-after-bad situations. Service limits are the minimum specifications that a new part may wear to before it has to be junked at overhaul. In other words, when the engine is opened for overhaul, a part may be at the ragged edge of service limits, yet it's perfectly legal to reinstall that part. During the first hour of service as an "overhauled" engine, the part could wear beyond the service limits. A part worn beyond service limits isn't necessarily unsafe, but it narrows the safety margin. This is the sort of overhaul that someone might perform on an airplane that is for sale. "Zero time since major overhaul" may sound attractive in an ad, but caveat emptor. If the seller can't verify that the overhaul was to new limits, it's probably not a good deal.
I chose an overhaul to new limits because I wanted assurance that the parts had as much service life as possible without paying for a lot of new nonmoving or noncritical parts. I chose new cylinders because they are the hardest-working parts in the engine and the ones most likely to fail. Plus, competition from the likes of Superior Air Parts and ECI has driven down the prices for all new cylinders to the point that new sets are not a lot more expensive than overhauled ones, especially if you factor in the greater warranty that comes with new parts.
How about that propeller? As with engines, propellers are not required to be overhauled at the manufacturer's recommended time-between-overhauls interval when used under FAR Part 91. Many props live a hard life with little attention. Mine hadn't been off the airplane in 12 years and 1,200 hours. At an average of 2,400 rpm, that's almost 173 million revolutions. With the engine out, it's a good time to overhaul the prop and the governor that controls it. Other accessories also deserve a look. A typical overhaul often includes the replacement or overhaul of the starter, magnetos, and ignition harness. Vacuum pumps, alternators, and exhaust systems are accessories not usually included in an engine overhaul. With the engine apart, it's a good time to overhaul or replace those components as well.
I had gotten used to the stiff throttle cable in my airplane, but others balked at using two hands to push it in for priming. I had the shop install a new one. Mixture and propeller control cables, hoses, and engine mounts are other items that should be looked at and probably replaced during an engine overhaul.
A major overhaul on a big engine can set you back the price of a very nice car (trust me on this). You can ruin the whole thing by leaving in place your busted-up, bent, torn, and worn-out engine baffles. Baffles are misleading. They look so simple and dopey. Yet, they are critical to delivering the proper cooling air throughout the cowl — to both the engine and accessories. Even a small hole can have a dramatic effect on cooling a particular cylinder. Spring for replacement baffles if yours are at all questionable. I replaced all of the baffling along the inlets on each side of the propeller.
Once you've made all these decisions, sit back and wait for your engine to return. The wait will seem interminable. My wait is over. I should be flying in a couple of days. But then there's the break-in period, which is, literally, another story.
E-mail the author at [email protected].
