Occasionally disassemble and overhaul the air compressor. Remove the compressor coupling
from the shaft to prevent damaging the bearings. Before disassembly, clean the compressor and mark
the parts so that they can be reassembled in the same positions.
Maintain the oil in the compressor crankcase at proper levels according to maintenance
schedules. Clean out the crankcase when the oil is changed, but do not use any flammable cleaning
materials. If the oil pressure is too high or too low, check the oil relief valve and pump and the filters.
Remove and inspect cylinder liners and pistons. Hone all cylinders retained in service. After
honing, check the clearance between each piston and cylinder with piston rings removed. Also make
certain that the cylinder flange face is perpendicular to the cylinder bore. Replace the crankshaft if it is
bent or cracked, or if the bearing seats are worn excessively. Check valves for lift and for wear limit.
Examine main bearings for general condition and proper end clearance. Disassemble the compressor
governor; clean and oil it approximately once a year. Clean or replace strainer element.
2.15.
TEST OF REPAIRED ENGINES
Each repaired diesel engine should be operated and checked before it is released for service.
Time, fuel, and labor spent breaking in the engine will result in greater longevity and efficiency of the
unit. A check is made of compression pressures in each cylinder; exhaust gas temperature for each
cylinder at various engine speeds; lubricating oil pressures and temperatures; cooling water
temperatures; supercharger or blower pressures; horsepower output under varying conditions of current
and voltage, as indicated by the main generator characteristic curve; individual throttle position speeds
and loading; color and quality of exhaust gases; and general sound and action of the engine under load
and acceleration.
Action of the engine under conditions simulating the engine under load can be tested by sending
the current from the main generator through an electric dynamometer that measures the generator's
output. A "liquid rheostat" or "water box" also enables an engine to operate at different speeds, as
though it were installed in a locomotive pulling different loads. A water box is seldom used, however,
because of the danger of electrocution. Other facilities for testing an engine include a cylinder pressure
indicator, either the maximum instantaneous pressure type or the curve drawing type; pyrometer
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