Gas Engine Magazine

The Donkey Engine

By Staff

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.

  • Published on Aug 1, 1990
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