The Donkey Engine

Curtis air compressor

This is a picture of a Curtis air compressor that I, George, converted to a gasoline hit and miss engine. In the background is a picture of the rest of our engines, along with our hauler. I started on this winter project around the first of November, 1989

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111591 Hartness Road Statesville, North Carolina 28677

Now, here is a brief history of what it is made of and the problems I encountered. I first made the camshaft. I used a cam out of a 230 cubic inch Chevrolet that I cut down to 9 inches long. All the camshaft lobes were cut off except the one that I used to operate the exhaust valve. The distributor drive gear was left to drive the magneto that came off of a Wisconsin engine and to drive the hit and miss governor. I cut the end off a 302 c.i. Ford. I then drilled the end of the crankshaft and fitted the stub and gear off the end of a 350 c.i. Chevrolet crankshaft to it. The timing chain is off of a big block Chevrolet. I then took the compressor cylinder head and modified it for gasoline. I next proceeded to adapt the cam to the compressor. I took a 4-inch piece of channel iron and butted another piece to it and welded. I knocked out one piece of channel where it would slide back over the edge where the crankcase bolts together. It is fastened to the block by four existing bolts. I made the cam pillars out of one-half inch steel and cam bearings out of aluminum and brass. There are oil holes drilled in the pillars to keep the cam oiled.

I next proceeded to make the governor, which is constructed mainly of aluminum. The arms that the flyballs are fastened to are made out of one-fourth inch key stock. The balls are chromed gearshift balls. The governor slide sleeve is made of aluminum, and is loaded with the solenoid spring out of a Delco starter.

I next proceeded to make the shaft to drive the governor, which is made out of solid brass. I attached a distributor gear to it to drive the governor. I then used a hole saw to cut a hole in the channel to line up with the gear on the cam. It took three trys before I got it right.

I next made the mounting plate for the rocker arm and stand which came off a 216 c.i. Chevrolet. I next cut holes in the plate to accommodate the governor shaft and pushrods. The valve push-rod is made out of three-eighths inch cold rolled steel. The governor control is made out of one-fourth inch cold rolled steel. The latch is made of one-fourth inch steel. The braces that support the rocker arm mounting plate are one-fourth inch cold rolled steel.

Next I proceeded to mount the magneto. The drive is made of solid brass with a distributor drive gear attached to the end. A one-half inch stud slides in the end of the gear and is fastened to a plate that supports the driveshaft. I had to remove the impulse on the mag because of too much strain on the small gears, resulting to the use of battery power. The carburetion consists of three-eighths inch brass fittings and the flapper valve is made of a three-eighths inch cast iron union and a flat freeze plug. The gas tank is made of a two quart orange juice can.

Now is the time to see if it will run. I worked about two hours before I got it to hit a lick, and when it did, it blew the head gasket. I had too much compression, so to remedy that I had to make a new cylinder head. The head is made out of a four and one-half inch by three inch piece of solid steel. I cut the combustion chamber one-half inch deep by three inch diameter, and the valves came from a Toyota with the heads cut down to three-fourths inch diameter. I used a Briggs & Stratton valve spring and keeper for the exhaust valve. When I tried cranking it again, it would hit, but would not crank. I needed a little more weight to get it over, so I attached another flywheel to the other side of the compressor, which was what it needed, as I got it running with a little help from another engine. After I got it running, I got other carburetor adjusted to where it would crank with about one to two turns by hand. After about fifteen minutes running time, the governor gear wore out, and I had to make a change in the lineup of the gear, which worked out alright.

I also made a lifter which screws on the end of the exhaust valve pushrod. This is the history of my homemade hit & miss engine.

The rest of our collection consists of the following: Fairbanks Morse Z A 6 HP; ZA 3 HP; ZD 2 HP; Stover Economy 2 HP; IH 11/2-21/2 HP LA; IH 3-5 HP, LB; Delco light model 850; Delco light 4 B-12; Wisconsin AHH 9 HP; Maytag Model 92; and a Briggs & Stratton Model 9.