Compressor Engine
(Page 2 of 3)
February/March 2004
Robert Best
Moving Ahead
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The head ended up presenting the biggest headache, and at one
point I thought I might have to cast a new one to make the engine
work. The head was originally equipped with a -inch pipe outlet and
-inch pipe inlet that protruded about 1- inches above the top. I
ended up plugging these with cast iron pipe plugs, which I then
drilled out to act as valve guides. I fabricated the valves from
5/16-inch stainless steel rod that I welded to 1--inch-diameter
stainless steel heads. I then ground the valves to a 45-degree
angle so they would seat properly. I ground the valve seats into
the head, and I determined final valve length when I fabricated the
exhaust rocker arm.
The big problem came when I was trying to add material to make
ports for the exhaust and inlet. I had the valves set into the
vertical pipe, but I then needed to port the vertical pipes
horizontally, which required a creative solution.
I decided to weld in horizontal ports, but as many of you know
welding heavy cast iron can be problematic, to say the least. After
adding material to port the valves, I had small pin-holes in the
ports that I couldn't close. To get around this I reamed the
ports out. I then pressed in a -inch piece of threaded pipe for the
exhaust, but I used smooth pipe on the inlet side so I could
install a slip joint for the carburetor. I fabricated the
carburetor from a piece of 1--inch brass with a venturi of
approximately -inch, which I bored for the needle valve and seat.
Next, I fabricated a 25-ounce-capacity brass fuel tank that I
installed directly below the fuel mixer seat. This gives me enough
gas to run the engine all day.
I then fabricated the exhaust rocker arm and cam, and with some
trial and error to get the right lift on the valve, it worked out
fine. I also fabricated brackets to support the cam gear and shaft.
The trick here was to attach the top bracket on the head before
finally drilling it for permanent location so I could adjust the
alignment of the shaft. It wouldn't take too much misalignment
to wipe out the gears.
Ignition is by buzz coil with an adjustable wipe system mounted
on the cam. The wipe is adjustable to regulate timing. I also added
a spark saver since the engine coasts so long between ignition
cycles. I made the flyballs for my governor from 1 -1/4-inch brass.
I was anxious to fire it up, so before I made the fuel tank I shot
some fuel into the carburetor. The engine fired, but the fly-ball
shafts were so long the engine wouldn't fire again so I
shortened the shaft lengths. I ended up changing the length of the
flyball shafts three times before I found the correct speed.
Springs can be added to the bottom of the flyballs to increase
engine speed, but to keep the engine running slow, I've left
the springs off. Now fully functional, this engine runs between 100
rpm and 150 rpm, and after it hits it coasts 12 to 15 revolutions
before firing again.