ENGINE AR 3N1129 - Caterpillar

Unloader
A new cylinder head maintenance kit should be used when rebuilding. The entire contents of this kit must be used. Failure to do so may result in compressor failure.The unloader pistons in the kit are prelubricated with a special lubricant and need no additional lubrication. Install the springs and unloader pistons in their bores being careful not to cut the O-rings. Install the unloader cover gasket and unloader cover and secure the cover cap screws. Tighten the cap screws to 20 to 25 N m (175 to 225 lb in) in a crossing pattern after first snugging all screws.Discharge Valves, Valve Stops And Seats
If the discharge valve seats merely show signs of slight wear, they can be dressed by using a lapping stone, grinding compound and grinding tool however it is recommended that a cylinder head maintenance kit be used. Install new discharge valve springs and valves. Screw in the discharge valve seats, and tighten to 52 to 66 N m (70 to 90 lb ft). Discharge valve travel should be between 0.75 mm (.030 in) to 1.17 mm (.046 in). To test for leakage by the discharge valves, apply 700 kPa (100 psi) to the cylinder head discharge port and apply a soap solution to the discharge valve and seats. Leakage in the form of soap bubbles is permissible. If excessive leakage is found, leave the air pressure applied and with the use of a fiber or hardwood dowel and a hammer, tap the discharge valves off their seats several times. This will help the valves to seat and should reduce the leakage. With the air pressure still applied at the discharge port of the cylinder head, check for leakage around the discharge valve stop on the top of the cylinder head casting. No leakage is permitted.Inlet Valves And Seats
Inlet valves and springs should be replaced. However, if the inlet valve seats show signs of slight nicks or scratches, they can be redressed with a fine piece of emery cloth or by lapping with a lapping stone, grinding compound and grinding tool. If the seats are damaged to the extent that they cannot be reclaimed, they must be replaced.