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.
  • VW-sourced sideshaft gears
    Clearly visible VW-sourced sideshaft gears.
  • Switch-breed
    Sideshaft, rocker arm and exhaust lock-out on the 'Switch-breed.'
  • Sketch of Switch-breed
    A sketch of Vernon's 'Switch-breed' highlight's the governor and exhaust lockout that he fabricated for the conversion.

  • Switch-breed compressor engine
  • VW-sourced sideshaft gears
  • Switch-breed
  • Sketch of Switch-breed

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.