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Having grown up in an automotive machine shop, as well as with an aviation background, Chris Collum was well-prepared when he went into the Marine Corps as a crew chief on CH-53 Echo Super Stallion helicopters. Having served from 1989-1993, Chris picked up new skills and honed some existing ones when it came to his aircraft engine knowledge.
He got out of the Marine Corps in 1993, and started doing cylinder work for people as a side gig, while also working at some other aircraft shops, flight schools and things of that nature. In 2009, he began working three days a week at Airworx Aviation, an aircraft engine machine shop located in Brewton, AL. The shop opened its doors that same year. At the time, Chris was also working four days a week at another shop – until 2015.
“In 2015, I had a snow skiing accident, and that other shop decided they didn’t need me anymore, so I started working four days a week at Airworx and I’ve been doing it ever since,” Collum says.
Today, Chris is COO of Airworx Aviation, which has five employees. He’s also the accountable manager, which handles communication with the Federal Aviation Administration (FAA) since Airworx is an FAA-certified repair station. The aircraft engine machine shop is 3,200 sq.-ft. and also includes a 500 sq.-ft. clean room for assembling the engines
“We’re one of the only aircraft engine shops in the country that does all of our own machine shop work, the assembly as well as the test runs afterwards all in-house,” Collum says. “Our focus is strictly on machining engines, running them and then shipping them back out to the customers. We don’t work on any full airplanes or anything like that. It’s strictly the heartbeat of the plane.
“We do Franklin air-cooled engines, which we’re one of the only shops in the world that actually has a Part 145 Repair Station to build those engines. We also do Lycoming engines and Continental engines as well. These engines are what you would call opposed cylinder reciprocating engines, and they can be built up to about 550 cubic inches.”
Airworx customers are a mix of individuals with airplanes and contract work from companies. Collum says most of the engines his shop works on are akin to big, glorified Volkswagen engines. He says there’s some differences in the engine models themselves, but they aren’t too dissimilar from automotive engines.
“The clearances are close to the same,” he says. “The biggest thing is the certification process. The paperwork and the requirements you have to meet on certifying aircraft engine parts is a lot. You have to keep up with a lot of tags and certificates when you do an airplane engine versus a Volkswagen or a 350 Chevrolet.”
While all the machine work is done in-house, Airworx will send out a special process called cadmium plating and heat treating. They also send out any overhaul work that needs to be done on accessory components such as magnetos or carburetors. For testing, the shop does have an engine dyno, but it isn’t completely set up yet, so Collum uses a run stand and what they call club props, which utilizes the same instrumentation that the aircraft itself would have in it.
“The three engines we work on are all so similar,” he says. “The tolerances on the Franklins are much, much closer than Lycoming or Continental engines are. And that’s the engine that’s probably the least supported as far as parts go. We have to do a lot of different things on those engines. Continental and Lycoming, both of those companies are still in business, so parts availability, tech support and things of that nature are pretty good on those. Those two engines are more common to see in the shop.
“These engines go into general aviation airplanes – everything from old Piper Cubs, all the way up to Piper Navajos or Beech Dukes or Cessnas.”
Recently, as part of a 10-year contract Airworx Aviation has with one of its company clients, the shop needed to overhaul a Lycoming O-360-C4P engine out of a Piper Super Cub that had 2,000 hours on it.
“The Lycoming O-360-C4P engine is a four cylinder, 360 cubic inch, roller cam engine,” Collum says. “This engine showed up for an overhaul based on the amount of time it had on it, which was right at 2,000 hours. When the engine comes in, we completely disassemble the engine, clean it, do a visual inspection, and we do a dimension check on everything. Then, we do all of our non-destructive testing (NDT) work.
“Once that’s done, we’ll go in and line hone the cases and grind the crankshaft and have it nitrided. We’ll also grind the camshaft and grind the lifters. We overhaul the connecting rods by putting bushings in the small end and resizing the big ends, as well as new rod bolts and new nuts. We also overhaul the rocker arms.
“Typically, we install new cylinders, but new cylinders have been hard to come by, so we’ll take and overhaul the old cylinders and put in new valves. We don’t do any performance mods. All of our work is in accordance with federal regulation. We use aftermarket parts from companies that have manufacturing approval. We use Superior Parts a lot for things like bearings, cylinder kits, and the majority of the internals.”
With the machine work done, Airworx then uses a chemical coating on the aluminum parts called Alodine, which allows paint adhesion to the aluminum.
“We mask and paint all of our detail parts piece by piece separately instead of after assembly,” he says. “Then, once everything is final inspected, it all comes to the assembly room and the assembly guys jump on it.”
Accessories such as magnetos and carburetors get sent out for overhaul to a repair station called QAA. Once those parts come back, they’ll go on the engine and Airworx will put in a new ignition harness from a manufacturer in California, and new Champion aircraft spark plugs before the engine is ready for the run stand.
“The engine will get run for about four hours,” he says. “You must run the engines for a certain amount of time at a certain rpm, so we go through all of those rpms and time and make sure everything falls within the scope of the overhaul manuals.”
Back in tip-top shape, this Lycoming O-360-C4P engine is capable of 200 hp at 2,700 rpm, and it will help power a Piper Super Cub aircraft that pulls tow planes off the ground and up to altitude before releasing them.
Engine of the Week is sponsored by PennGrade Motor Oil, Elring – Das Original and Scat Crankshafts. If you have an engine you’d like to highlight in this series, please email Engine Builder Editor Greg Jones at [email protected].
