Section III. PRINCIPLES OF OPERATION
General, Principles of Operation
Power Train Assembly
The theory behind the operation of the forklift is described in the following paragraphs. Each system is dependent upon the
other for efficient operation of the forklift. The information contained herein will assist maintenance personnel in
understanding how the forklift functions. This knowledge will assist in isolating components which have failed.
The powertrain assembly supplies the power required to move the forklift and operate the hydraulic system
pump. It converts the energy from burning fuel to rotary motion to drive both the transmission and hydraulic pump. The
powertrain assembly consists of the following components:
Four-cylinder, diesel fueled, water cooled engine
Six speed transmission (3 forward speeds, 3 reverse)
Front and rear driveshafts
Front and rear axles
Speed range and direction selector
Service brake and inching pedal
Differential lock system
Oil pressure gauge
Coolant temperature gauge
Transmission oil temperature gauge
Engine Fuel System. The function of the engine fuel system (Figure 1-6 and 1-7) is to inject clean, atomized
fuel into engine cylinders at a precise time near the end of the compression stroke of each piston. Components of the
system contribute to the delivery of fuel to the cylinders.
The engine is equipped with a cam-actuated lift transfer pump. Fuel flow begins as the lift pump pulls fuel
from the supply tank. The pump supplies low-pressure fuel (21-35 kPa, (3-5 psi)) to the fuel filter head, through the fuel
water filter/separator and fuel filter, and to the injection pump.
The injection pump builds the high injection pressure required for combustion, and routes fuel through
individual high-pressure fuel lines to each of the four fuel injectors. When high-pressure fuel reaches an injector, pressure
lifts an injector needle valve against spring tension to let fuel enter the combustion chamber.