Surrendering your engine to an overhaul shop has a bit of a dice roll to it. Shops quote prices for the overhauls, but they’re based on a “repairable or serviceable core.” That means a good crankshaft and a crankcase and either or both could be junk, propelling the overhaul into blank-check territory in the blink of an eye.
Even though they’re just a lump of cast aluminum, crankcases do wear out and before that, they sometimes crack. Is it better to replace a knackered case with a new one, fix what you’ve got or let the shop draw an overhauled case from the repaired inventory pool? That last option is by far the real-world solution of choice, but there may be circumstances where a new case is justifiable.
The good news for Lycoming owners is that the company has recently, and quietly, dramatically reduced prices on new crankcases and we’re not talking a measly 15 percent, but more like 60 percent. That doesn’t automatically argue for a new case, but it makes it more palatable if yours is irredeemable scrap.
Core In, Engine Out
Most overhauls these days take at least six weeks and some take longer than that. The bottleneck, shops tell us, is sending crankcases out for rework and getting certain parts from suppliers, either the two major manufacturers or the PMA houses that ply the overhaul trade. When turned in for overhaul, all crankcases need some work, ranging from minor cleanup and dressing of mating surfaces to more major work, like weld repairing major cracks, line boring for the bearing webs and reworking the tappet bores. Most overhaul buyers don’t see this on the invoice because it’s included in the price of the overhaul.
“Our pricing is conditional that the case be serviceable,” says Allen Weiss of Certified Engines, which was in the midst of moving from Opa-locka to North Perry Airport when we called. “Same thing with a crankshaft. But a lot of times, a case rejects and you have to hit them with a core charge,” he adds. So what does serviceable mean? The exact definition probably varies by shop, but it universally means that at least the case meets the specifications described in the approved overhaul manual.
It specifies specific dimensions for main bearing and tappet bores, the condition of the mating surfaces and accessory case bores, deck height and so forth. Most cases coming in for overhaul require at least some work, but perhaps 20 percent get by with just cleanup and inspection, says Tim Hansen, at Penn Yan Aero in Penn Yan, New York. There’s some variability in what constitutes a serviceable or repairable case. Hansen says Penn Yan promises an overhaul to new dimensional limits, not service limits, as some shops offer. The shop also backs that up with a long warranty—five years or TBO, whichever comes first.
At the other end of the spectrum are crankcases that arrive beaten down to the limits of reparability, with worn bores, fretted mating surfaces and cracks that may or may not be weldable.
A cracked crankcase might not have to be taken out of service if it’s discovered on the mount. In fact, Continental has a service bulletin describing continued service with minor cracks. But during overhaul, cracks must be repaired or the case replaced; no overhaul manuals allow cracks.
AC 33-6 describes in detail the repair processes used for crankcases and cylinders. Weld repairs are allowed in crankcase bores, in supports, webs and fillets of the bearing bores and around stud holes, cylinder decks and mating flanges. Cracks up to 3.5 inches are considered repairable, but anything longer is not.
Not all crankcase repairs require welding. In fact, many don’t. Things like worn tappet bores can be bored and fitted with oversize sleeves and main bearing bores, which wear out-of-spec due to fretting between the case halves, are routinely line bored to restore an aligned bed for the crankshaft. Where crack welding is required, all evidence of the crack must be removed, welded and the entire case heat treated. It sounds like a complex process and it is.
That’s why most engine overhaul shops send their crankcase work to one of two major vendors in the industry—DivCo or Crankcase Services, both in the Tulsa, Oklahoma, area. Turnaround time is typically six weeks and shops tell us this is almost always the bottleneck in turning around engine overhauls, although obtaining some parts can also slow things down.
For this reason, many shops maintain a pool of repaired and serviceable cases. If a core has a cracked but repairable case, the shop will draw one from its pool and send the cracked case to Oklahoma for repair. Owners also have the option of buying a new crankcase and some choose to do that.
“The problem we’re running into currently is that the customer doesn’t want to pay the upgrade charge for that new product because it’s really not reasonable,” says Stephen Boggess of RAM Aircraft in Waco, Texas. They’re a Continental specialty shop with a focus on the 520/550 series, but they also overhaul some Lycoming engines.
When we spoke to Boggess in late February, the shop had 67 serviceable cases in stock covering just about all of the large-displacement Continental engines. These typically sell for less than half of the cost of a new case, which can top $10,000. Since shops must stand behind their engines with increasingly competitive warranties, it’s fair to ask if a repaired case really is as good as a new one.
“The key thing is was the repair done right, ” Boggess explains. “Honestly, the biggest reason we find for cracking is maintenance. These engines don’t get to TBO without some cylinder work. We found that a lot of engines with cracking have had some kind of cylinder work done in the recent past. And maybe they didn’t get it torqued properly or to the right amount. That has proven itself in the logbooks,” he adds.
Certified’s Allen Weiss agrees that properly repaired cases are no more likely to have cracking or other issues than new ones. Certified builds about 300 engines a year and Weiss says the shop might see a return on a case once a year, if that. Although vendors like DivCo will stand behind their repairs, they don’t reimburse the engine shop to break the engine down and redo the overhaul. Certified stocks more cases than any other shop and had about 150 when we interviewed Weiss in February. They often sell to other shops that don’t keep a repair pool on hand or who can’t wait for a turnaround repair from DivCo or Crankcase Services.
A handful of shops are approved to do their own repairs. Penn Yan Aero is one and Central Cylinder Service in Omaha, Nebraska, is another. They work to the same standards observed by the specialty crankcase vendors, but can offer faster turnaround for customers.
While there are a lot of old crankcases out there that have been beating around for 30 or more years, shops we contacted don’t establish any limits for maximum hours on a case they’ll put back into the field. “We believe in having them repaired if they meet standards,” says Certified’s Weiss. “For us, it has more to do with how many overhauls the case has had, not total hours. Two or three overhauls is the limit for us,” he adds.
Crankcases have only so much metal to work with and when the mating surfaces are re-machined and the bores line bored, the dimension between the crank journal centerlines and the top of the cylinders—the so-called deck height—necessarily gets smaller. If it gets small enough, the piston won’t have enough clearance on the compression stroke and the case is ready for the scrap yard.
As the field overhaul shop universe has contracted, so too has the range of parts suppliers shrunk and become more competitive. Until recently, for instance, Lycoming and Continental cases were supplied by the original manufacturers, ECI and Superior, plus the aftermarket repair pool. But ECI was bought by Continental in 2015 and that rearranged the market. ECI no longer competes with Continental on its own cases, although it does compete with Lycoming for Lycoming cases.
Furthermore, Continental has shifted its distribution predominately to Aviall and prices have escalated, according to shops we spoke to.
Lycoming did some rearranging of its own in response to this. Quietly at the end of last year, it drastically reduced prices on crankcases and crankshafts and not by a little. Heretofore, the company sold crankcases only as kits, which included such accessories as through bolts and spacers.
“A lot of shops don’t want those parts,” says Lycoming’s Steve Palmatier, so the company broke the package into discrete parts. Furthermore, he says, Lycoming did a reset on costs and margins and routinely reviews everything in its parts catalog. “We looked at costs on components and the selling price and sales volume and realized we aren’t selling any of these,” Palmatier adds. Just as a for instance, the price on one case—an IO-360 with flat tappets—was dropped from $17,501.63 to $4979.65, a decrease of a whopping 72 percent. Palmatier told us some products are a little more than others, but this range of price reduction is typical.
The industry noticed. “Just overnight, the industry lost about a million dollars on that deal,” says L.J. Warren, president of Zephyr Aircraft Engines in Zephyr Hills, Florida. He’s referring to the investment some shops have in inventory of repaired cases. What used to be a breathtaking upcharge for a new crankcase is now far more affordable.
“When they’re already spending that much money on an overhaul, $900 extra to get something new rather than something used and rebuilt, they’ll almost always buy the new one,” says Central Cylinder’s Dan Czarnecki. Other shops report similar responses from customers. Lycoming’s move upended the crankcase market but, unfortunately, only for Lycoming cases. Continental crankcase prices remain relatively high. “We really need Superior to step up in this market,” says Weiss of Certified Engines.
With Lycoming cases priced so reasonably, we think any owner who needs one because the core case is junk should tilt toward new. Shops say new Lycoming production is less likely to crack because of product improvements so saving $1000 on a repaired pool crankcase hardly makes sense. If the submitted core needs a repair, that’s already baked into the overhaul quote so it probably doesn’t make sense to upgrade to new.
For Continental owners it’s more complicated. New cases are still expensive, perhaps adding a third to the cost of the basic overhaul. A repaired case will cost half that, if not a little less. The good news is that repaired Continental cases seem relatively abundant so for most popular engines, there shouldn’t be a delay in getting one to keep the overhaul perking along.
CAMSHAFTS: STILL A PROBLEM
Our interviews with engine shops revealed a troubling trend that may be getting worse. “The number of camshafts and tappets we see with spalling is epidemic,” says Allen Weiss at Certified Engines. While other shops see the same thing, they don’t necessarily agree on the cause or the frequency.
While spalling turns up when engines are broken down for overhaul, it’s also common on engines sent in after a prop strike—even low-time engines. While some shops say it has to do with low utilization, Weiss told us Certified sees it in frequently flown flight school aircraft.
So what’s going on? Greg Merrill and Ed Kollin think they’ve found a smoking gun. Merrill is general manager of Aircraft Specialties Services, which does cam and tappet overhaul, and Ed Kollin developed the Camguard oil additive marketed by Aircraft Specialties.
Independently, Merrill and Kollin picked up a pattern in aircraft logs related to cam spalling. They noticed that engines that had spalled cams and tappets were frequently topped within 100 hours of the cam going south. Kollin’s theory is that before the cylinder is broken in, it has about 10 times the combustion blowby that a fully broken in cylinder would have. Blowby gasses get past the rings and load the oil up with undesirable combustion byproducts, including lead salts, water and unburned fuel.
Kollin also believes that the oil gets contaminated with a family of chemicals called hydroperoxides, also a combustion byproduct. He says hydroperoxides have a unique—and damaging—ability to prevent lubricating oils from forming a protective film on the surface of wear parts. Cams are especially vulnerable because the contact surfaces between the cam lobes and the tappets are under as much as 100,000 PSI of pressure.
The lack of an oil film, Kollin says, causes microwelding or microscuffing that begins with minor pitting. The pits create stress risers and eventually cause the surfaces of cam lobes or tappet faces, or both, to progressively degrade.
When new cylinders are installed on an engine, the recommendation is to operate it on straight-weight mineral oil for 25 hours. But Kollin says that’s too long and should be limited to an hour, after which the oil should be changed and the engine run for another 10 hours on mineral oil before switching to an AD type.
Kollin also believes subtle changes in oil formulation contribute to the process. Aeroshell, for instance, used to contain more sulphur than it does now. Sulphur is a natural lubricant and is antagonistic toward hydroperoxides. Lower flying activity contributes by adding potential corrosion into the mix. Kollin and Merrill say the solution is to simply change the break-in oil much sooner than is usually recommended.