Curtis Switch-breed
The Story of an Engine that Never Was - Until Now
April/May 2004
Vernon Achord Jr.
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Vernon Achord's Curtis 'Switch-breed' compressor engine looks for all the world like an original stationary engine.
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My part of this story starts in June 2003 at the Hill Country
Antique Tractor and Engine Club Show in Stonewall, Texas. I was
talking to Randy Carll, who always has something interesting for
sale, and I told him I was looking for a small compressor from
which to build an engine. He pointed to a small, old air compressor
he was selling. It was stuck, but the price was right so I bought
it, along with a Monitor engine and several other items. He even
threw in another compressor so he wouldn't have to haul it
home.
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After I got the compressor home I dismantled it, and fortunately
it didn't take much to un stick the piston. With the engine
apart, I could take stock in what I had and make my plan of attack.
This compressor has a forged crank and rod, and a 2-1/8-inch bore
by 2-1/4-inch stroke. A dipper for lubrication is mounted on the
crankshaft, and the engine has a hollow base.
One problem with converting compressors to engines is that most
do not have any combustion chamber. They were designed to compress
air, not to fire a charge, so the piston comes very close to the
head on top-dead-center.
About the same time I was working on this project, GEM featured
another Curtis compressor engine in the September 2003 issue. The
fellow who converted that engine used a 1 -inch spacer between the
cylinder and the head to give the engine a combustion chamber. I
figured 1 had three choices: I could build another head with a
combustion chamber (it would also help with the valves and ports),
shorten the connecting rod or use a spacer.
Unfortunately, I don't have the tools or the iron to build a
head. I liked the idea of shortening the rod, but there was nowhere
in the original head to nowhere in the original head to put a
spark plug, so I ended up using a spacer. To use the original head,
I ground a new valve seat and moved one using my dremel tool. I
turned valve guides from rod stock and pressed them in the head,
and used valves from an old Clinton lawn mower engine.
I don't own any sideshaft engines, so I figured this would
be the time to have one. For sideshaft gears, I used the crankshaft
and distributor gears from an air-cooled Volkswagon engine. These
gave me the 2-to-1 ratio I needed for the valve. I took a thick
flat washer, turned it down and pressed it inside the crank gear.
Then I drilled a 1/8-inch offset hole in it and the crankshaft, and
used a 1/8-inch dowel to keep it in time.
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