Steam Engine Build/Piston Connector Rod

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Steam Engine Build Instructions


The connector rod connects the piston stem to the crank on the crankshaft. One end is fixed to the piston stem and travels in a reciprocal, linear motion. The other end is attached to a crank on the crankshaft and travels in a circular motion. The crankshaft end contains a bearing case and ball bearings to reduce wear on the crankshaft.

The connector rod is built up from three elements:

  • Coupler
  • Bearing Case
  • Rod




Bearing Case

Connector Rod Assembly






Using a piece of high quality steel:

  1. Cut a 1.5" length from 1.0" square bar stock
  2. Drill a 0.5" dia hole in one end to a depth of 0.75"
  3. From the top face, drill a 0.25" hole at 0.5" from the left end.
  4. Cut a slot 0.25" wide to meet the hole just drilled.
  5. Bevel the piece at a 45 degree angle as shown
  6. Drill a 0.25" hole 0.25" from the end into the side face

Bearing Case

The bearing case can either be milled from high quality steel, or the circular portion turned on a lathe and bolt tabs welded on.

  1. Drill bolt holes 0.25" dia.
  2. Inside bore is 1.2" dia to hold a bearing unit with a 1.0" bore (shaft size)
  3. A cylindrical channel is cut inside 0.5" wide and 0.647" deep


  1. Cut a length of 0.5" rod 5.0" long
  2. Insert the rod into the coupler and weld it
  3. Insert the rod into the bearing case and weld it.