Lightning crank

The lightning crank is a special design of the drive pin in which the drive rod does not engage directly on the original drive pin but on a crank. The purpose of this arrangement was to subsequently change the crank offset on a three-cylinder locomotive, in which both outer crank pins were 90 ° ahead of the inner crank pin.

The lightning crank was only used on the Altona 561 and Altona 562 steam locomotives of the Prussian State Railways . These locomotives had a three-cylinder compound engine, with the outer low-pressure cranks running 90 ° ahead of the inner high-pressure crank. This arrangement was made on a trial basis with these locomotives in order to counteract rotational movements around the vertical axis, which occur in locomotives with 120 ° crank offset.

Since the new arrangement resulted in strong twitching movements of the locomotive in a certain speed range, this idea had to be abandoned, and the locomotives were rebuilt in 1904 or 1905 using lightning cranks in such a way that the lightning crank now lagged the drive pin on the left side by 45 °, while it ran 45 ° ahead of the drive pin on the right, so that there was a total offset of 45 ° / 225 ° / 90 °. Since the high-pressure cylinder acted on the front drive axle, the rear drive axle was offset by 90 °, as is common with two-cylinder locomotives.