BODY GP-TRUCK 2773201 - Caterpillar

Testing And Adjusting
The air pressure gauge will show low air pressure in the system when air system checks or tests are needed. Air system checks are needed if the needle in the air pressure gauge keeps moving when the components in the air system are not being used.
AIR SYSTEM SCHEMATIC
1. Air line between tank and air compressor. 2. Head for air compressor. 3. Inlet air line from engine manifold. 4. Air governor. 5. Air tank.The complete air system, including the components in the air system, must be checked for any air leaks. The air lines must have no breaks and all of the air line connections must be tight and have no air leaks. If all of the air leaks have been stopped and the air pressure gauge still has indications of low air pressure further tests are needed.
TYPICAL AIR COMPRESSOR INSTALLATION
1. Air line between tank and air compressor. 2. Head on air compressor. 3. Inlet air line from engine manifold. 4. Air governor. 6. Cover over unloader valve. 7. Adjustment screw.Stop the engine and let all of the air out of the tank (5) and the air system. Disconnect line (1) from the cylinder head (2) to the air tank.Start the engine and let it run for a minute. With the engine running hold a white card approximately 2 in. (50.8 mm) from the opening in the head (2), where air line (1) was disconnected but for no more than 10 seconds. A large area of oil on the card is an indication of wear either in the bore of the liner or the piston rings (and piston). A little oil in fine drops is an indication of correct lubrication. If the card test shows no wear, connect air line (1) and let the air compressor fill the air tank until the air pressure gauge will not indicate any more pressure.Run the engine at low idle speed and disconnect air inlet line (3) from the cylinder head (2). With the engine still running slow, hold your hand close to the opening in head (2) where air line (3) was disconnected. If air can be felt coming from the opening when the piston of the air compressor is on the compression stroke, the inlet valve is not closing. Either the unloader valve under cover (6) is holding the inlet valve open or there is dirt on the inlet valve holding it open. A broken spring under the inlet valve will also keep the valve open.The unloader valve can be cleaned by removing cover (6), spring (8) and unloader valve (9). Clean the unloader valve and the passage in the head where the unloader valve fits.Install the unloader valve, the spring and the cover. Torque for cover (6) is 60 lb.ft. (8.3 mkg). Start the engine and feel for air coming from the opening where air line (3) was disconnected, if air can be felt the inlet valve is not closing and the head assembly must be removed to