Steam locomotive drivers are "quartered". The crank pins are set 90 degrees apart.
The process of aligning the pins is called quartering. This is usually done in a jig. All the drivers must be quartered in the same manner to avoid binding, caused by one driver not being in phase with the others. All must be done at the same time, using the same jig, as no two jigs are alike.
When working on a steam locomotive, it is very important, since if the drive train binds or jams, the decoder could be damaged or destroyed. Older brass may need this checked and adjusted to obtain smooth operation before conversion to DCC.
Quartering is a big job, requiring a lot of time and patience. The entire drivetrain must be adjusted and any corrections made so that the wheels will rotate freely. For more info and tools, see the NorthWest Shortline Website at:
As a rule, if the engine runs fine, do not mess with it. The process of aligning, adjusting and quartering should only be done if there are problems. Tolerances are in the range of a few thousands of an inch.
In real life, a locomotive could not start if the drivers were not quartered. They also spent a lot of time adjusting and shimming bearing blocks to line up the wheels correctly with respect to the rest of the rotating assembly.
NWSL makes a number of specialized tools for maintaining locomotives, such as pullers for removing wheels from the axle.. They also sell gearboxes, motors and wheel sets.