Movement No. 169 is a refinement of Movement No. 168, replacing the slotted crank with a short link to connect the pitman to the main crank. In No. 168, a pin on the pitman slides in a slot on the main crank — introducing sliding friction and wear. Here, a rigid link replaces the slot, pivotally connecting the pitman to the main crank pin. The intermediate shaft still carries a second fixed-radius crank connected to the same pitman. The two cranks and the link together constrain the pitman’s motion so that its connection point still traces a near-elliptical orbit, preserving the power-transmission advantage of the original mechanism. By eliminating the slotted joint, this modification reduces friction, wear, and backlash — resulting in smoother, more efficient operation at higher speeds. This linkage approach is mechanically cleaner and more durable, representing a practical engineering improvement over the slotted-crank version for steam engine applications.
169. A modification of 168, in which a link is used to connect the pitman with the main crank, thereby dispensing with the slot in the said crank.