To dampen the action of the governor, which is inherently very sensitive, some kind of drag is used. In the Fairbanks Morse engine the drag is introduced by the action of a small plunger A, Fig. 293, placed in a recess in one of the weights. The outer end of the plunger bears against a wrought-iron angle bolted to the inner face of the flywheel rim. The plunger is kept in contact with the angle iron by the coil spring B. It is necessary to give this plunger considerable side clearance to allow it to move freely. The drag of the governor tends to cause the plunger to bind on one side of the cavity at the top and on the other side at the bottom of the plunger. This wears the cavity out of true and causes the plunger to wedge, resulting in the governor hunting. If the wear becomes pronounced, the proper method of adjustment is to drill the recess to a larger bore and turn up a new plunger to fit it. Since it is easier to make a new plunger than to enlarge the recess, the plunger should be made of mild steel; it will then receive all the wear while the recess will keep its shape.
The Rites governor, also, advances the point of injection, or "admission," and increases the eccentricity, or the pump plunger travel, as the load increases; see Figs. 294 and 295. The full lines in Fig. 294 show the positions of the crank, eccentric and weight arm at low load. The eccentricity is OA, and the crank is a degrees from dead-center when the eccentric begins to move the push-plunger B. It should be understood that an eccentric strap is used on this governor, and the pump plunger receives .its motion from the action of the eccentric strap and push-rod. The point B, which represents the end of the pump plunger, is for clearness and simplicity shown as being in contact with the eccentric. The weight arm and eccentric swing on the pivot C. The positions under full-load conditions are shown in Fig. 295, as well as by the dotted lines in Fig. 294. In changing from low load to full load, the eccentric center moves from A to A', and the eccentricity increases from OA to OA'. The beginning of fuel injection, or admission, is made earlier since the crank is now a e degrees from rear dead-center when the eccentric begins to act on the push-rod. As with the Muncie governor, the throw of the eccentric exceeds the pump plunger stroke, the travel of the eccentric, until the operating rod strikes the pump plunger or push-rod, being the "lap." As mentioned before, early injection is advantageous when using heavy oil, as it allows more time for the oil to vaporize; consequently, a given size of engine will carry a greater load than it would if the governor did not advance the injection admission.
It should be borne in mind that the position of the weight arm pivot, relative to the position of the crank and the center of the eccentric, largely determines the actual action of the governor. While the governor should be designed to allow the speed at no load to be above the full-load speed, it is possible, by proper distri bution of the weights and the spring tension, to cause the engine to speed up on full load.
The relative positions shown in Figs. 294 and 295 closely ap proximate those on the governors in use. The eccentric is made in one piece with the weight arm, and no means are present to change the angle of advance. The pump, however, has a stop whereby some adjustment can be made as outlined in the dis cussion on page 387.
Fairbanks-Morse Fuel Pump.—The fuel pump used with this governor is shown in Fig. 296. It consists of a bracket pump body into which are fitted the valves and plunger. The plunger is hardened and ground, and no packing is used. The plunger is forced to the rear on the suction stroke by the spring shown. Its suction travel is limited by the plunger stop "99." This is pro vided with a fibre tip, which wears and must be renewed at in tervals. The plunger stop is bored out, allowing the eccentric push-rod to work through it against the end of the pump plunger. The stop can be screwed in or out, thereby adjusting the suction travel. This alters the speed and provides a means of manipu lating the injection timing, as will be discussed later in the chapter. Since the Fairbanks-Morse engine does not use water injection, the adjusting of this stop allows the engineer to deaden preigni tion pounds. If the engine pounds, the screwing-in of the stop will cause the preignition to cease. If the engine slows down due to overload or slow-burning oil, the screwing-out of the stop will cause the oil to be injected earlier and in slightly greater amounts.
The suction and discharge valves are of steel and are of the spring-loaded poppet type. The seats are at an angle of 45 degrees, while the lift should not exceed inch. In regrinding these valves nothing but the finest of emery flour or rotten stone mixed with vaseline should be used. Care should be taken that all the parts are thoroughly clean on reassembling. In tightening up the cap lock-nuts, if the operator is not cautious, the brazed joint between the sleeve and the oil pipe will break.