Curtis Switch-breed

The Story of an Engine that Never Was - Until Now


| April/May 2004



Switch-breed compressor engine

Vernon Achord's Curtis 'Switch-breed' compressor engine looks for all the world like an original stationary engine.

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.

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.