Stuffing-box.—The stuffing-box has a screw gland and is best packed with lead or babbitt shavings or strings. This packing conforms to the valve sufficiently to. prevent the loss of air and does not become hard as does all composition packing.
Valve Spring.—The valve spring is of a length that allows the needle valve to be reground before the initial compression of the spring is lost. An iron washer placed above the spring will give the effect of a lengthened stem. However, the valve cannot be used after it is worn short enough to cause the spring plunger g to drop below its housing.
Fuel Line Check Valve.—The fuel line has a ball check valve immediately at the valve cage. This ball, in time, wears, allow ing the high-pressure air to back through the oil line to the pump. This causes the line to become air bound.
Fuel Valve Rocker Arm.—The rocker arm is of two-piece con struction and fulcrums on an eccentric bushing, which carries the air-starting rocker. The valve end of the rocker has an adjusting screw that can be manipulated to provide the required clearance between the roller and the fuel cam.
Fuel Cam.—The fuel cam is fitted with an adjustable steel nose. The nose is slotted and is held by two countersunk screws. This allows a considerable shifting of the nose. After the nose is set in position, it is locked by end shims. These shims are best made of wrought iron and should be hammered until the entire recess is filled; the surface should then be smoothed with a file to conform to the curvature of the cam.
Eccentric Rocker Bushing.—As has been mentioned, the fuel rocker arm is fulcrumed on an eccentric bushing, which also carries the starting rocker. On a four-cylinder engine the two inside cyl inders are fitted with starting valves. When the engine is to be started, the eccentric lever o of these two cylinders is thrown into the starting position, Fig. 82. This revolves the eccentric bush ing until the fuel rocker fails to engage its cam while the starting rocker comes into contact its cam. The levers of the outside cylinders (1 and 4) are set to "neutral," which disengages the fuel rocker and cam. As soon as the air line valve is opened, the two starting cylinders turn the engine over. After one or two revolutions of the flywheel, the levers of 1 and 4 are moved to the running position, admitting fuel to the fuel valves. When
these cylinders start firing, the levers on No. 2 and No. 3 cyl inders are moved from the starting to the running position, cutting out the air-valve mechanism and engaging the fuel rockers.
Servomotor.—On the larger Busch-Sulzer engines the timing of the fuel injection is altered at load changes. This is accom plished through the agency of a cylinder placed in front of the engine, containing a spring and piston. This cylinder is in com munication with the low-pressure cylinder of the air compressor. The air-compressor suction is provided with a damper arrange ment actuated by the engine governor. On low loads the air to the compressor is throttled. This results in a lower discharge pressure in the low-pressure cylinder; this, in turn, lowers the pressure existing in the servomotor. The spring then forces the piston downward. The piston rod moves a system of levers that actuates an auxiliary roller which is linked to the fuel valve rocker. This layout appears in Fig. 116. It will be noted that as the air pressure in the servomotor becomes lower, 'due to a lighter load, the auxiliary roller a moves upward, thereby allow ing the cam nose to strike it slightly earlier in the engine cycle. The auxiliary roller is in contact with the fuel rocker roller b at all times, being held by the links c. The auxiliary roller is set in such a position that if the injection opening is early, as on low load, this roller remains in contact with the cam nose for a smaller interval. Consequently, on full load the period of injection be gins later and extends over a greater crank angle than it does on low loads. This is shown in Fig. 116 where the dotted lines indicate the roller positions on low load and the full lines are the full-load positions.
On starting the engine, the of the servomotor is raised to the half-load position while the air from the air compres sor to the servomotor is cut off. This latter action is for the purpose of preventing the servomotor from moving the injection roller to the full-load position. Frequently, when the engine is using heavy oil, it is necessary to adjust the servomotor hand wheel to provide for earlier admission than the air pressure would give, or vice versa with heavy oil on light loads.