Komatsu GD621A-1(S/N 10001-UP)

The GD621A-1's S6D105-1 diesel runs mechanical injection with no engine controller, so trend data comes from fluid sampling, not fault logs. Pull engine oil, transmission/torque-converter oil, and tandem final-drive oil samples on a set interval to track wear metals and coolant contamination before a bearing or clutch pack fails. Watch the monitor panel's individual warning lamps at every start and warm-up cycle: oil pressure, charge, and coolant-temperature lamps are the only onboard alert this grader gives.

Expect wear at the articulation joint bushings, circle-drawbar ball-and-socket, and wheel lean cylinder seals from sustained grading loads. Blade lift cylinder seals and hydraulic fittings around the circle drive are common leak points on high-hour units. On the S6D105-1, mechanical injection pump and injector service is the usual fix for hard starting or smoky exhaust, since there is no electronic fuel trim to mask a worn pump. Tandem final-drive seal leaks show up as oil weeping at the drive wheels.

At high hours, the torque-converter transmission clutch packs and tandem final-drive bearings and gears are the major rebuild items on the GD621A-1's driveline. Measure circle gear teeth and drawbar ball-stud wear before they cause blade chatter, and plan to replace wear plates as a set. Engine top-end overhaul on the S6D105-1, injectors, valves, cylinder liners, follows once oil-sample trends or a compression check flag it. Frame articulation pins and bushings also need periodic play checks and replacement on this articulated-frame model.

Cold-climate starts on the mechanically injected S6D105-1 benefit from a block heater or starting aid, since this generation predates electronic cold-start assist. Drain the fuel tank water and sediment trap more often in wet or humid grading conditions, and check coolant antifreeze concentration before winter. In dry, dusty grading work, service the air cleaner and pre-cleaner more frequently to protect the mechanical injection pump from abrasive ingestion. Grease circle and articulation points more often after wash-downs or wet-season operation to purge trapped moisture.