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Chuck Fellows,     Cave Creek, AZ

Two Cylinder Engine Project                1/7/2006

This is a two cylinder engine project I have under way.  The bore is ¾” and the stroke will be about 7/8”.  The flywheels are 3.56” diameter and weigh about 13 oz each.  The entire engine, thus far, is made from steel.  The bottom plate is ½” thick cold rolled steel, and the upper part of the engine is made from 1.25” x ¼” angle iron.  The crank was turned from 3/8” x 1.25” cold rolled steel.  The journals are all 5/16” in diameter.  The cylinder block  is 2 ¼” wide, 2” long, and 1 ¼” thick.  The head is 2 ¼” x 1 ¼” x 5/8”

The engine will be powered by compressed air and will be 4 stroke in operation.  Timing gears of 2:1 reduction ration, one on each side of the engine, will drive a camshaft at half the RPM of the crankshaft.  The cams will operate push rods which pass under the cylinder block and open the overhead valves  through rocker arms.  There will be one push rod and one overhead valve per cylinder.  I have designed a unique valve structure which will divert air from the cylinder through an exhaust port in the cylinder head when the intake valve is closed.   The intake can remain closed for as many cycles as desired and the exhaust port will remain open the entire time.  This is particularly useful for hit n miss operation.  When the intake valve is opened by the rocker arm, compressed air entering the cylinder head activates a secondary valve which seals off the exhaust port, applying all the pressure to the cylinder and the piston therein.

 With the two crank lobes at 180 degrees and the 4 stroke operation, I hope to attain an operating sound similar to the old 2 cylinder John Deere’s and 2 cylinder Lister’s. 

11/27/2006  The engine is finally finished. I had actually finished it about 3 months ago, but had to redo the head and the valves since I wasn’t happy with the operation.


The engine is a two cylinder, with the crank throws 180 degrees apart. Bore is ¾” and the stroke is about 5/8”. It runs on compressed air which is controlled by one overhead valve per cylinder. The engine is 4 stroke in operation, with the camshaft driven at one half the speed of the crank. This is accomplished through gears as in a normal 4 stroke. The valves are normal, automotive style poppet valves but the air is not admitted directly into the cylinder. Instead, a spring loaded sliding valve is inserted between the poppet valve and the cylinder. When the poppet valve is opened by the cam, air pressure forces the sliding valve to move about ¼”, closing off the exhaust port and channeling the incoming air into the cylinder. When the poppet valve closes at the bottom of the stroke, spring pressure returns the sliding valve to its normal position, opening up the exhaust port and allowing air from the cylinder to exhaust. Since springs hold the sliding valves in the “exhaust” position, the engine will freewheel with no compression.

I have the valve timing set slow so that the engine will “idle” at about 300 rpm and it’s top RPM is limited to about 1000 rpm. At both idle and wide open, the engine sounds very much like an old John Deere 2 cylinder tractor, which, of course, was my intent since I’ve always been captivated by the sound of an old John Deere Tractor. The combination of the poppet valves and the clicking of the sliding valves create a pop very much like an internal combustion engine.

All that’s left is to disassemble the engine, clean it up and paint. Of course, I plan to use John Deere green as the main color!



Copyright 2006,  Florida Association of Model Engineers and engine builder as noted above, All rights reserved.