Midwest Steam Motor Rebuild
February 27th, 2003

Take a close look at that crankpin! (photo below) This engine was still running when I decided it was time to do some work on it.  This was a simple and enjoyable process that involved some basic lathe work to create a new piston, connecting rod, crankdisc, crankpin, crankshaft, and cylinder head. I also drilled out the cylinder to 19/64" and then reamed it to 5/16" to create a truly cylindrical bore with a reasonably good finish.  The cylinder head was integral with the cylinder in the original design.  I decided to drill through it (from the opposite end) so that I could run the reamer all the way through to ensure the best possible bore.  There is a third step (smallest diameter) on the new cylinder head that I made to reduce the clearance volume to a minimum.  Clearance volume is the  "dead space" left above the piston when at top dead center.  Steam engines are more efficient when this volume is minimized.  Not shown was the bushing I made of 5/32" OD K&S tubing for the crankshaft.  The original bearings were so worn that there was over .06" "wiggle" at the end of the crankshaft.  ...Yet - it was still running!  The moral of the story is: Don't go overboard on trying to achieve precision fits when building or rebuilding a steam engine.  Sure, some components deserve more attention than others, but in general this is a very forgiving technology.  While I was at it, I drilled and tapped the flywheel for a 4-40 setscrew to allow for future disassembly.  The original Midwest motor was designed to be soldered together.  Last, I carefully refaced the port faces on both the cylinder block and the engine frame by lapping them on 400 grit silicon carbide sandpaper on a hard, flat surface.  I washed everything thoroughly before I reassembled it.  The engine ran well as soon as I applied steam pressure.  It should get even better as the newly machined surfaces "bed in".  All in all, a very rewarding mini-project.