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March 13, 2008
By Ian J. Twombly
By Ian J. Twombly
The business end. The work horse. The powerplant. All are colloquialisms for one key part that defines an airplane—the engine. In the context of AOPA’s “Get Your Glass Sweepstakes” Archer, that engine is a Lycoming O-360-A4M, one of the most popular light aircraft engines ever built. For this year’s sweepstakes, we wanted the engine to be the best it could possibly be, so we turned to one of the country’s most reputable shops to help.
Penn Yan Aero has been overhauling aircraft engines for more than half a century, so it was natural for us to turn to the small, central New York-based company to help us get the O-360 back to top form.
Although saying top form may be a bit unfair. After all, the engine only had a little more than 600 hours on it since it was remanufactured at Lycoming. Factory remans, as they’re called, allow owners to start an engine’s time clock back at zero, just one reason they are popular options when it comes time for an overhaul. But since the Archer’s engine was scoring in the high 70s on compression tests, was burning very little oil, and showed no other signs of slowing down, a good, reliable overhaul was in order to give the sweepstakes winner the best airplane possible.
Overhauling an engine is not entirely unlike refurbishing an airplane. The object in question is stripped to the core, and then cleaned, repaired, and serviced before being reassembled again. In the case of an engine overhaul, owners have many options. Other than dedicated overhaul facilities such as Penn Yan Aero, one can get a factory-remanufactured engine, a new engine, or have the engine overhauled in the field by a certified airframe and powerplant mechanic. But for the overhaul that best balances value, efficiency, and quality of work, a Penn Yan Aero overhaul is hard to beat.
The process began when Oxford Aviation, the Maine company doing the paint, airframe, and interior work, crated up the Archer’s engine and sent it to Penn Yan’s facility. Because Penn Yan only needed the engine and not the airplane, the time apart is a great opportunity to get an engine overhaul while redoing a panel, or getting new paint or a new interior. After Penn Yan completes an inventory of all parts, the engine is stripped and completely taken apart. All the pieces are placed on a cart that will be that engine’s resting place for the entire process.
A very complete and thorough cleaning comes next. “Think of it like a big dishwasher,” said Bill Middlebrook, Penn Yan’s owner. A hot water and detergent solution ensures years of grime are flushed down the drain. This is now the opportune time for an inspection. A variety of techniques are involved to make sure every piece that isn’t in proper working order is addressed. These run from a simple visual inspection to sophisticated instruments that measure bore diameters with air. Afterwards, necessary replacement parts are ordered to ensure they arrive in time for the reassembly.
Next is a critical phase in the process. Penn Yan Aero quotes engine overhauls as a flat rate. Need new valves? They’re included. So are seals, rods, and almost every other part. The two exceptions are the crankcase and crankshaft, both of which are very expensive. In fact, a bad crankcase is one reason an owner might opt to forgo the overhaul process and go straight to a factory reman, knowing the savings of an overhaul may have been erased. But for those who do go the overhaul route, help is available. Penn Yan has the authority to make three repairs on a case. If more are needed, it doesn’t matter if the area is non-critical, the case must be replaced. And that means money and delays.
Assuming the crankcase is in good shape and can be repaired, the cylinders are addressed. Options abound at this stage. Penn Yan Aero can overhaul an owner’s cylinders in many cases, but more will select factory new, like we did for the Archer. Aftermarket options are also available.
Concurrent with cylinder work is the accessories. As part of the quote, Penn Yan will overhaul or replace the carburetor or fuel injectors, provide a new wiring harness, new spark plugs, and a lightweight starter from Sky-Tec (more on that next week).
Now in the final stages, the crankshaft is dynamically balanced. Middlebrook said his shop does it best because instead of just balancing the shaft, the flywheel is attached. Too often, he said, a shop will just balance the shaft and then the entire engine will be out of balance when the flywheel is eventually attached.
Finally, the entire thing is reassembled. Here, technicians with experience measured in decades carefully and methodically piece together every nut, bolt, and fitting. Attention to detail is paramount, and even little touches like zip ties are placed on the wiring harness.
Owners can opt for one nice extra step, something that we think will make the engine a true standout. The Archer’s new engine has “chrome” valve covers and a beautiful dark gray metallic paint to match the exterior. It is a striking thing to behold when you first see it.
As a key safety feature, a good reliable engine is something not to be overlooked. We think we added considerable value in these terms with Penn Yan’s overhaul. Now the winner will not only have an airplane that looks good and has significant utility, he or she can feel safe while flying it.
Next week: Engine accessories
E-mail the author at firstname.lastname@example.org
Flight Training Editor Ian J. Twombly joined AOPA in 2003 and is an instrument flight instructor.
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