The connecting rods are made up of several components all working together to transfer linear motion from the pistons into rotational motion on the crankshaft.

The rods are steel with bronze split bearings at the bottom or “big end”. The upper crosshead bearings utilize bronze bushings.

I began by stacking both rod blanks in the mill to shape the upper ends and drill the hole for the cross head bolt.

 

I used an aluminum jig to set up the rod for profiling the side tapers.

 

The main rod bearings are milled blocks of bronze that were split and surfaced.

 

After splitting the bearing block, machining the mating surfaces, and fitting the halves together with superglue, I used four pieces of scrap aluminum held tightly against the sides with a rubber band to precisely indicate and center the bearing block in a four jaw chuck.

 

Boring the center hole prior to reaming to final size.

 

Test fitting a crank journal pin after reaming.

 

Profiling the outer rings of the bearings.

 

Back over to the mill to profile the exterior of the split bearings. These outside grooves are for securing the bearings in place within the rod straps below.

 

Both rod straps were machined out a single piece of steel and then split apart.

 

After drilling the mounting holes and rod bearing wedge adjustment slots.

 

Rod bearing adjustment wedges.

 

I fabricated a simple jig to position the main rod bearing at a precise distance from the cross head bearing in order to drill the through holes for the rod bearing strap. This assured that both rods were built to the exact same length (6.250″ between centers).

 

Fully assembled connecting rods.

 

Cross Heads

The bronze cross heads are attached to the tops of the connecting rods and the piston rod. The cross heads move up and down in the cross head guides on which the cylinders are mounted.

Bearing bronze blanks were turned in the lathe to match the inside diameter of the cross head guides.

 

The sides were milled down and various features were machined such as drilling and tapping the cross head bolt hole and creating oiling ports for the cross head bolt bearing.

 

Finished cross heads fit nicely into the cross head guides.

 

The cross head bolts are machined from steel hex stock, turned and threaded to size.