Operation and maintenance manual

Starting Motor QSB4.5 and QSB6.7
Page A-20 Section A - Adjustment, Repair, and Replacement
If the crankshaft does not rotate or requires more than the
normal effort to bar, check for an internal malfunction or a
problem with the drive unit and/or accessories.
If the engine cranking speed is too slow/will not crank at
all, and the engine rotates freely:
Make sure the wiring connections are clean, tight, and not
damaged.
Check the battery voltage. Refer to the OEM service
manual.
Check the voltage at the starting motor during cranking. If
the voltage drops more than 2.4-VDC on a 12 volt system
and 4.8-VDC on a 24 volt system, check that all
connections are clean and tight.
If the cables are correct and the voltage drop exceeds the
limit, replace the starting motor.