Compressor Engine

Missouri Collector Breathes New Life into Au - To Air Compressor

| February/March 2004

  • Vintage stationary engine
    Looking at the finished product, it's easy to see why some old iron collectors mistake Robert Best's converted Au-To compressor for an original, vintage stationary engine.
  • Mixer
    Robert welded in horizontal intake and exhaust ports after fitting valves to the original suction and discharge pipes. The mixer (at right) is hand-made.
  • Vertical fly-ball governor
    Robert's converted compressor features a vertical fly-ball governor. Note the linkage for exhaust lockout on overrun, plus the integrated spark-saver. Very nice work.
  • Gear set
    A distributor gear set from a Volkswagen drives the vertical flyball governor and camshaft. Robert also cut out material from the base of the cylinder to expose the crankshaft.
  • Compressor engine
    Looking very much like a factory-built engine, Robert's converted Au-To compressor engine is an attractive and certainly unique engine.

  • Vintage stationary engine
  • Mixer
  • Vertical fly-ball governor
  • Gear set
  • Compressor engine

I wonder how many collectors have ever seen -much less owned - an Au-To flywheel air compressor? Better yet, how many collectors have seen an Au-To air compressor converted to an engine?

After seeing a few engines made from air compressors some 15 years ago, I decided to make my own. I attended numerous auctions looking for a compressor that would make a good engine, and for $5 I picked up an Au-To compressor. The old compressor sat around my shop for a while, and then I moved it to my storage building, where I forgot about it until 2002.

Getting Started

Picking the project back up, and not sure exactly how to proceed, I worked on my engine by trial and error. Using some drawings of other engines as a guide, I finally adapted a concept I thought would work.

I wanted the finished engine to have dual flywheels, but the compressor was only fitted with a 14-inch flywheel on one side and a ring gear of equal size on the other, which, I assume, was geared to an engine that supplied power to the compressor. For the second flywheel, I used one from a Cushman Binder engine. It's a little larger, but at some point I'll turn it down on a lathe to the same size as the original. The Cushman flywheel had a tapered center hole, so I reamed it straight and installed a steel bushing to size it to the Au-To's 1-1/8-inch crankshaft.

I sourced a 2-to-1 distributor gear set from a Volkswagen, which I decided would work well to drive the vertical flyball governor and camshaft I planned on fabricating. Not surprisingly, the Volkswagen distributor gear set also had to be sized to fit. Fixing the larger drive gear was no problem, as all I had to do was machine a bushing to reduce its inside diameter to 1-1/8-inch. I knew I'd have to machine the smaller driven gear, but it was so hard I had to anneal it before it could be machined. I did this by heating it cherry red and slowly cooling it in a bucket of sand. Then I turned it on a lathe to match bushings that I had available.

The compressor's original crankcase was completely enclosed, but I thought the finished engine would look nicer if I removed some of the non-essential cast iron housing at the base so people could see the crankshaft.


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