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I always wanted to build a 4 cycle gasoline engine since I was a kid. In the
past, I have built several steam engines. I was looking on the internet and found
plans to build a hit-n-miss engine. This sounded like a great retirement project.

I bought the plans. The engine was designed by Harold Despenbusch from
Kansas. When I looked over the plans, the project was a lot bigger than I had imagined. ( ) This is not a beginners project to say the least.

The engine is one quarter scale horizontal cylinder water cooled engine similar to a Faribanks Morse Farm engine of the 1920's.

The specs on the engine are:
Bore and stroke 1 1/8" by 1 ½" The compression ratio is about 7 to 1.

The engine is a 4 cycle overhead valve type. The intake valve opens automatically on the intake down stroke of the piston. Exhaust valve opens with a push rod to the cam.

Ignition is spark and is produced with a magneto coil stolen from a lawn mower engine. The engine magneto coil is operated as a spark coil with a 6 volt battery. Points on the valve push rod fires the coil and spark plug.

The valves are machined from a piece of ½ inch drill rod and are set into steel valve guides pressed into the aluminum head. The valve seats are aluminum. They are ground to a 41degree angle.

The bottom end of the cylinder is open and the crankshaft and connecting rod are obviously seen in the photos. The cylinder is lubricated by a drip oilier. The main bearings and rod bearings are lubricated with grease cups and zerk fittings.
The main bearings are of bronze oilite material.

The engine is water cooled. As can be seen a water hopper surrounds the cylinder. There are ports drilled into the aluminum head for additional cooling.

Carburetion is achieved by a needle valve and jet off of a McCoy 35 model airplane engine and a simple venturi tube.

There are 2 keyed flywheels whose diameter is 5 ½". Mounted on one flywheel is the flyweights for the hit and miss governor.

There are about 90 individual parts that have to be made for this engine. I have
a lathe and mill and a lot of accessories, which allowed me to do all the work on
making the parts. I did purchase the timing gear, pinion and cam from Mr.
Despenbusch. Those were the only parts that I purchased with the exception of
a donated model airplane engine spark plug. The remainder of the parts were
made from raw metal stock.

The crankshaft was fabricated using ½" drill rod and some cold rolled steel for
the crank cheeks. This assembly was silver soldered to form the crank.

The engine base was fabricated with individual pieces of 3/8" thick steel plate
and welded together.

It took about 2 ½ months of time to finish the engine. I'd estimate about 100
hours of time spent on it, although I didn't keep a real good track of the time.

The toughest part of the job was making the flywheels. I got some ¾" steel plate
and cut out the blanks for the flywheels with a portable band saw. I then
machined the counter bores on both sides to form the hub and rims.

Then I milled the spokes which was a tough job. Last but not least I found it necessary
to cut keyways in the crankshaft and flywheels. Set screws wouldn't hold the
flywheels on. You can see my "poor man's broach" pictures.

This is by far the most time consuming project that I have ever undertaken except
for the restoration of some antique cars in the past.

The engine runs quite well but I did have some difficulty with seating the piston
rings. Which required a break in by driving the engine with an electric motor in
the seating process.

When you play the video of the slow speed retarded operation you can see the
valves working and hear the timing gears, valve tappet and the delightful chuff of
the exhaust.

Click here to view engine running

Close your wmv player to return to this page.


Dan Smith 11/22/06