G3304 and G3306 Engines Caterpillar

Air for the starting system comes from an air compressor or an air tank. Pressurized gas can also be used. The duration for rotation of the flywheel is determined by the volume, air pressure, and air restriction.

For starting engines which do not have heavy loads, use an air pressure of approximately 690 kPa (100 psi). This pressure provides a good relationship between the duration of the flywheel's rotation and the cranking speed.

If the engine has a load which cannot be disconnected during starting, the air pressure regulator must be adjusted in order to provide enough speed for starting.

The maximum pressure for use in the air starting motor is 1030 kPa (150 psi).

For good life of the air starting motor, ensure that the air supply is free of dirt and water. Use a lubricator with "SAE 10W" nondetergent oil for temperature above 0 °C (32 °F). Use air tool oil for temperatures below 0 °C (32 °F).

Illustration 1	g00737979
(1) Start valve (2) Lubricator (3) Starting motor (4) Relay valve

Illustration 2	g00811855
Air starting motor (typical example) (5) Air inlet (6) Vanes (7) Rotor (8) Pinion (9) Spring (10) Piston (11) Reduction gears

The air from the supply goes to relay valve (4). The air flow is stopped by the relay valve until start valve (1) is activated. When the start valve is activated, pressurized air is supplied to piston (10). The air pressure behind the piston compresses spring (9). The spring moves the drive shaft and pinion (8) in order to engage the flywheel ring gear.

The air flow goes through lubricator (2). A tube in the body of the lubricator provides a vacuum above the oil in the bowl. Oil from the bowl enters the body's chamber that is attached to the air line. The lubricated pressurized air flows through air inlet (5).

The air pressure against vanes (6) turns rotor (7). The rotor turns the drive shaft and pinion (8) through reduction gears (11). The pinion rotates the flywheel ring gear and the crankshaft. The pressurized air is exhausted through the air outlet at the bottom of the starting motor.

When the engine starts to run, the flywheel will begin to turn faster than pinion (8). The design of the drive shaft for the pinion allows the pinion to move away from the flywheel in order to disengage from the flywheel ring gear. This prevents damage to the starting motor and the flywheel ring gear.

When start valve (1) is released, relay valve (4) stops the air flow to the starting motor. The air pressure to piston (10) stops. Spring (9) retracts the piston, the drive shaft, and pinion (8).