Jacking Gear

Jacking gear serves a similar function to turning gear but is designed for very slow manual or motor-driven rotation of the engine when no electrical power is available or when extremely precise positioning of the crankshaft is needed for maintenance tasks such as tappet adjustment or timing checks. On smaller vessels or generators the jacking gear may be a simple ratchet and socket arrangement applied to the flywheel; on larger installations it is a separate low-ratio gearbox. Jacking the engine through manually before starting is a standard safety practice after any maintenance that involved opening cylinder head covers or working near the crankshaft, ensuring that no tools or rags have been left inside the engine and that the engine turns freely through at least two full revolutions before the starting air valve is opened. This practice is supported by classification society safety management guidelines and many ship management company procedures. Engineers record jacking operations and pre-start checks in the engine room logbook, and any unusual resistance felt during jacking must be investigated before starting is attempted.