The PC-60 Military Surplus Engine in a Volksplane VP-2
by Dirk D. Kretschman
Dirk Kretschman in his VP-2 at the end of his runway (27XS). The converted PC-60 is spinning the 62-inch Hegy prop.
The Continental PC-60 is a four-cylinder, horizontally opposed, air-cooled, 201 cubic-inch industrial gasoline engine, rated at 70 hp (at 2400 rpm). It was used mostly by the U.S. Air Force as a stationary power source and also as a forklift engine. For the most part, it’s a spinoff of the Continental C-90 aero engine.
The five major ways a PC-60 differs from a C-90:
- It is skid-mounted rather than firewall-mounted.
- The intake ports are on the top of the cylinders like on a Rolls-Royce O-200 cylinder.
- The carburetor is mounted on top of the engine.
- One hole in the crankshaft flange is offset to match a flywheel, not a prop.
- It uses a single spark plug per cylinder with a single Slick 47-1 magneto.
Otherwise it is mostly an early C-90.
A CHANCE MEETING
How did I get involved with a PC-60? Well, in 1993 I went to the EAA’s Southwest Regional Fly-In (SWRFI) with my neighbor and future hangar mate, Captain Rick. While there, we ran into an old friend of Rick’s who also built an Evans Volksplane VP-1. (Captain Rick had built a VP-1 and but was then building a KR-2). When Rick and I told his old friend that I was building a VP-2 (the two-place version of the original Volksplane), he said he had the perfect engine for a VP-2, the PC-60. In fact he had two of them for sale.
The price was right so Captain Rick and I each bought one. We were lucky because Rick’s friend also had the U.S. Air Force -3 and -4 manuals to go with the engines. Let the fun begin! Not long after this chance meeting I found another PC-60, which at one time had been used on an airboat, in the corner of a friend’s hangar. So I bought it for $100 to play with and use as a mold when it came time to make the engine mount and a cowling.
After reading the manual several times and investigating other avenues, I found out that the United Kingdom’s Popular Flying Association (PFA, now the Light Aircraft Association) had conversion instructions for adapting the PC-60 to aviation use. The PFA sent me the instructions, and they were very good. On the surplus market in the United Kingdom, the PC-60 was a popular engine for homebuilders. I also had a C series overhaul manual to compare the two engines and as an aid in the overhaul of my PC-60.
First I had to set up an engine overhaul shop next to my project in the family garage. You know—things such as a 6-inch micrometer set, dial calipers, dial indicator set, and the other special tools needed. Some tools, like the magneto wire nut spanner and impulse-coupling spring tool, I had to make. I dropped off the crankshaft, camshaft, and connecting rods to be magnafluxed at an approved shop. I dropped off the cylinders at Engine Components Inc. (ECI) of San Antonio, Texas, to be honed and re-chromed back to “standard”, as some pitting of the cylinder walls had occurred. I found a source for 47-1 magneto parts in Chicago and overhauled the magneto. I built a magneto test stand using an old electric drill to drive the magneto and test the impulse coupling. If I was going to fly on a single magneto, I wanted it to be as close to perfect as possible. The test stand magneto was set up with four 3/8-inch air gaps; one for each plug. With the garage lights shut off, it was impressive to watch the sparks when it was running. I had full faith in the old 47-1 to carry me around, and it did so without fail, for 225 hours. Then I added a second set of plugs and two new Slick 2350 magnetos. I did not use shielded spark plugs or wires at first and made my own harness using the old AC-type aircraft plugs with the slide-down locking type of connector.
PUTTING IT ALL TOGETHER
The whole engine measured out to “new” limits, from the table of limits. The crankshaft, camshaft, and connecting rods came back with yellow tags. The cylinders were now like new, and it was time to follow all the conversion instructions the PFA sent me. The first major step was to have the crankshaft propeller flange re-drilled to open up the holes to fit a standard propeller bolt threaded bushing. I found a machine shop locally that could do that for me. By re-indexing the bolt circle slightly off center, one can do away with the single offset hole and have a standard propeller flange.
I used some propeller bolt bushings from an old O-200 crankshaft I had laying around. One can also just drill the propeller to fit the offset flange after clocking the propeller appropriately for hand propping. Another solution is to make an adapter to go between the crankshaft flange and the standard propeller. There are several advantages with having a standard propeller bolt pattern, though; one being that borrowing and testing other propellers is simple.
The next step was to blank off some unused oil galleries and the oil cooler ports if not used. Some of the unused oil galleries were blocked by drilling and tapping them in order to insert a threaded cap plug, and others were blocked with an external cover plate. Following this, I had to work on an oil sump. The stock PC-60 oil sump is a heavy, 12-quart, cast aluminum box structure. The standard C-90 sump is adaptable, but the VP-2 has a flat belly, causing the C-90 sump to stick way down and the filler neck to get in the way of the engine mount. I would have to modify too many things to use one, but I may still do it in the future. Instead I opted to use the original cast sump and modified it to hold only 4 quarts (231 cubic inches) by cutting it down and adding an aluminum plate welded to the bottom with a drain plug fitting in the back. The stock sump also has the oil temperature probe boss cast into it. The PC-60 now weighs in at 178 pounds.
With the stock oil pan holding 12 quarts being overkill,
Dirk opted to cut it down to 4 quarts. The lower engine
mount attach points were fabricated by Dirk and bolted
to the case. Larger view
Another little thing I did was to install an external engine oil filter that I picked up at a truck stop. The PC-60 already had the external oil filter housing installed where the old brass oil screen housing would have gone. I made the engine cooling baffles and inter cylinder baffles out of aluminum with a fiberglass eyebrow, which has worked out just fine. I put the crankcase breather in the same place as the C-90 and later added a homemade oil/air separator to the line. I blocked off the unused pads on the gear case and oil cooler pads. Remember to remove the oil cooler bypass ball and spring.
Dirk crafted a sturdy and ergonomic jig for holding
everything in place while a professional welder did
his thing. Larger view
I wanted to use stock C-90 engine mount rubbers so I turned (on a lathe) some steel bushings that would accept the C-90 parts. Next I fabricated and welded to the bushings fixtures that allowed me to bolt the bushings to the engine, in the correct location. This particular engine was originally skid-mounted, with the hard points underneath, and I wanted to use a more traditional style mount. I used the heavy carburetor mounting bolt holes on top of the case for lateral support as well as the generator pad through bolts in the accessory case. I used the lower aft skid-mounting points for the lower attach. One could opt to make a skid (or bed) mount, but again, I went with a more traditional method. Now that the engine was converted with the new bushings in the right place, the next hurdle was the engine mount itself. I built a jig to keep the four holes on the engine in the correct relationship to the four holes in the firewall, allowing the welder full access to all the joints. I spent a lot of time getting it just right, and it paid off the first time I mounted the engine to the firewall, as it just slid into place.
Although the lower engine mount attach points are
pretty straightforward, the upper points are a little
more elaborate, as this trial fit photo shows. Larger view
INDUCTION and EXHAUST
The next step was to make some welding jigs for the intake tubes and exhaust stacks. I used the flanged ends of the original intake tubes but fish-mouthed them for a cross tube that went aft to be connected to a “Y” and a vertical tube that would go down to the carb. I did about the same with the exhaust stacks (seen in the photo) but had the tubes bent in a muffler shop. I used the PC-60 carburetor heat muff, but I had to add some baffles and brass wool pads to get a good enough heat source. Later when I put on Champ exhaust stacks I used a real heat muff but still added a small internal baffle to it. I painted the engine and cylinders and assembled them as per the overhaul manual. I mounted it to the firewall and connected the instruments, controls, and fuel line.
Zenith Model 267 updraft forklift carburetor.
Now I was ready for a carburetor. I selected a Zenith Model 267 updraft forklift carburetor that would handle the CFM of the 201 cubic inch engine turning 2400 rpm. I changed out the main jet for the next smaller one at about 25 hours as I felt it was too rich in the mid to high range.
The carburetor has two float bowls for unlevel, multi-attitude work—like a skidder running up and down ramps at a warehouse might experience. It also has an equalizer or altitude compensation built in. I wanted a gravity-feed fuel system from my 16 gallon header tank, so I mounted the carburetor low on the firewall. The intake runners have three rubber joints between the carburetor and engine itself, so I was not worried about the vibration issue. The bottom of the carburetor bowl had a brass plug in it that I removed; in its place I installed a push-type fuel drain to drain the carburetor bowl, along with the gascolator, on preflight. I ran the choke control out to the back of the cooling baffle for easy access while hand propping. I use the choke only on very cold days.
To save space in the cowling, I used a flat K&N air filter just like the one on my 1989 Dodge Caravan. It worked perfectly. It’s mounted in the normal place in the cowling. I made the carb heat box and selector out of thin sheet brass and soldered it together. It, too, is mounted on the firewall.
After my Hegy prop (62/60) arrived, I bolted it on, took some pictures, and gave it a whirl. BANG-POP-VROOM! It started! I was not that surprised it actually ran (well, okay, maybe a little). It was almost overwhelming to see an engine running on my nine year long, almost finished project, tied down in my driveway while filling the back yard with smoke. My wife, who thought (or hoped) it would never fly, came to the window, and I think for a minute she was surprised it ran, too.
With the Volksplane finished, covered, and painted, Captain Rick and I moved it out to the airport. We moved Captain Rick’s KR-2 out to the hangar the same day. My son and I spent two months putting all those parts together. Funny thing, some of them I made so long ago I had trouble remembering how they went (but that’s okay, I’m over 60). That is one problem you don’t hear very much about on a long-term project like this, but it’s true. With the weight and balance, FAA inspection, and paperwork out of the way, I was out of excuses not to fly it.
There’s a lot going on in this photo, but if you look closely,
you can see the carb heat box, dual magnetos, and
choke knob, to name just a few details. Larger view
The dream of flying my own homebuilt actually started in February 1972 when I purchased the little info booklet Mr. Evans offered after reading about the Volksplane in the January 1972 issue of Sport Aviation. In 1975 I bought the plans for the VP-2, but in 1979 I took an overseas assignment that lasted 10 years, so the actual construction of my dream plane began in February 1993.
The first flight was August 25, 2002. There were a few issues to iron out during the test phase. One was that the propeller was way over-pitched. That made for fun when on climb-out; I was seeing about 100 feet per minute and only 2100 rpm. The airspeed indicator was 20 mph slow. I sent the propeller back and had it repitched, twice. The valve lifters do not like W100 aviation oil. Sometimes a lifter would stay pumped up, and on climb-out, that was not a fun feeling. Like the manuals for the A and C series Continentals say, use 30 weight oil for most temperature ranges. I started using 10W30 and now all is well.
I needed more carburetor heat. I have been told that Zenith carburetors are efficient atomizers of fuel; therefore, they are good icemakers. Here along the humid Gulf Cost, that’s a problem. It took me a while to catch on, but it is not a problem now. I added a small indoor/outdoor thermometer to the plane. I ran the outdoor probe up to the carburetor venturi body and made a clip to hold it and some silicon paste in place. Now I can monitor the carb body temperature while the thermometer is in the outdoor position. Monitoring the body temperature to a tenth of a degree while flying is relative. If it starts to get colder than when I first level off, I add carburetor heat and continue on my way. By switching it to the indoor position, I can read OAT for calculations. It works so well I can use it as a backup airspeed indicator. Speed up a little and it cools off a degree or two; slow down a little and it goes up a degree or two.
I have used both avgas and auto fuel and do not see any real difference. I read that using a blend of 75 percent 87 octane auto fuel and 25 percent 100LL avgas is close to 80/87 leaded avgas, so that is what I do most of the time. The PC-60 does not care.
With 225 hours on the engine, I removed the engine from the plane and dissembled it. I machined a second hole, installed a Heli-Coil, and added a second spark plug to each cylinder. While I had it apart I did another complete overhaul. All the parts except for one exhaust and one intake valve guide still measured out to new tolerances. I replaced the worn guides and some valve springs just because I had some new ones on hand. I went to shielded spark plugs and harness with the new magnetos.
When I put the engine back on and flew it I picked up 75 rpm. I now have 2500 rpm max with the second magneto, and it felt a lot stronger. Climb-out is better, too. At max gross weight (1,100 pounds) on a hot day I get a 375 fpm climb rate. Not an RV-like climb, I know, but certainly a 65-hp Cub/Champ climb rate. I still cruse at 2250 rpm (4.7 gph*), and that gives me a blistering 75 mph of open cockpit wind in the hair fun. *With an estimated brake specific fuel consumption (BSFC) of 0.5, 4.7 gph is roughly 56 hp.
SUMMING THINGS UP
As of the end of 2006, I had 300 hours’ total time on the plane, 75 hours since the modifications/overhaul, and it’s flying very well. I am looking forward to many more flying seasons with lots of blissful Volkspatroling in the Texas sky behind my PC-60 military surplus engine.
To answer your question of how much I have tied up in my PC-60, my official answer is, with everything I have done, about one-half of what one would pay today for a zero-time C-65 or C-85. And for your next question, how come it took nine years, well…the answer is simple; I never let the project get in the way of family activities. All that time, rain or shine, my poor wife was without a garage for her car. Just one of the little things she had to put up with during the project.
I am sure your last question is, where can I get a PC-60 engine? I used to see them in Trade-A-Plane a lot, along with the surplus O-290G, but now I see them on the airboat websites. Look around hangars, too. Parts are still around from surplus outlets like Alamo Military Surplus (505-325-2339) in Farmington, New Mexico, as well as others. Most repair parts can be purchased as Continental C-90 parts; I get mine from El Reno Aviation (800-521-0333). Neither Alamo Military Surplus nor El Reno Aviation seem to have websites. The pistons, valves, main bearings, and gasket kit, for example, are the same as a C-90.
I tried to drop a C-90 camshaft in, but the C-90 camshaft had a fuel pump or vacuum pump lobe on it and would not fit, so I set up my dial indicators and found out the C-90 and PC-60 camshafts had almost the same lift and duration. There are a few other PC engines out there, too. The PC-90 and PE-120. I think there is a smaller one also.
The glider pilot in Dirk came out when he adapted a handmade
Schweizer style tow hook to his tail wheel. It’s used to secure
the airframe before hand propping the engine. Larger view
The guys on the Volksplane e-mail list call Dirk “da Baron”
because of the German markings on his plane. This photo of
Dirk I found on the net certainly doesn’t help any.