Compressor Engine
Missouri Collector Breathes New Life into Au - To Air Compressor
February/March 2004
Robert Best
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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.
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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?
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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.
The compressor has a 3-inch bore and a 5-inch stroke, and at
top-dead-center there was only the slightest clearance between the
top of the piston and the head. But the Au-To also had a 1-inch
spacer housing the compressor's check valves, and by removing 3
inches from the center of the spacer 1 opened up a nice area for
combustion. The piston originally had four rings, but I took out a
ring as I figured three would be sufficient. Sure enough, the
engine has more than enough compression.
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