Figure 313 outlines the timing and the crank and eccentric posi tion. The flat surface of the cam M, which is keyed to the shaft, covers from 12 to 15 degrees, dependent on the engine size. When the crank C is in' he position shown, 3712 degrees from dead-center, the roller P moves the distance shown. The eccentric is now 8 degrees from mid-stroke. The eccentric is set at full load 60 degrees behind the crank. It will be clear from this diagram that the pump eccentric R begins its return or discharge stroke at a slight angle ahead of the front dead-center S, namely 22 degrees. The discharge stroke continues, regardless of the length of the stroke, throughout 180 degrees of revolution. The suction stroke continues for the other 180 degrees. It naturally follows, then, that the quantity of fuel entering and leaving the pump is in direct proportion to the eccentricity. On light loads the throw is small, and the pump stroke is also a minimum, resulting in a mini mum quantity of fuel, entering and leaving the pump; on heavy loads the amount is a maximum. Then the amount of fuel per degree of revolution of the engine varies with the eccentricity. Consequently, taking any small segment, such as the length of the flat on the cam, de, the amount of fuel that is pumped while the angle is being covered depends on the throw of the governor eccentric. The eccentric is so placed that the speed of the pump is at its maximum vahie when the cam flat 0 closes the suction valve F. It is apparent that, with this design of governor and fuel pump, the commencement and completion of the fuel in jection into the cylinder are constant at all loads. The only variables are the rate of travel of the fuel pump plunger per degree of engine revolution and the consequent rate of oil flow per de gree of revolution.
From this discussion it is obvious that the velocity of the oil jet issuing from the injection nozzle varies with the load. This probably accounts for the better full-load combustion, since the oil atomization is nearer perfect at a high jet velocity. The op erator is seldom called upon to alter the setting of the cam. While it is keyed to the engine shaft, if an adjustment is decided upon, an offset key can be used to hold the cam in its new posi tion. A slight alteration in the timing of the suction valve may be obtained by adjustment of the tappet f. This is a rather delicate procedure as a matter of two turns of the screw will cause the valve to remain open during the entire cycle. If the tappet is adjusted very closely to the plunger, the suction valve opens early and closes late, resulting in an excessive fuel charge, which will be indicated by a smoky exhaust and, at times, by blowing of the relief valve. When the roller is in the center of the flat surface on the cam, the clearance between the valve plunger f and the tappet should equal the thickness of a piece of writing paper. Having this clearance, at its maximum upward travel, the suction valve opens considerably before the end of the flat has been reached by the roller and closes some degrees after the roller strikes the flat. As already stated, the actual valve closure covers from 2 to 3 degrees although the cam flat is from 12 to 15 degrees in extent.
Reverting to the pump, the suction valve demands a certain amount of attention. The valve is closed by the action' of a strong spring, and a heavy blow is occasioned to the flat valve seat. This in time will wear. To correct this a light cut should be taken from the valve and the valve seat. The adjustment should be finished up by regrinding with emery flour and vaseline: In later built Bessemer engines the suction valve is equipped with a small auxiliary valve. This is opened a trifle ahead of the main valve, thus relieving the pressure and making it easy to open the main suction valve. In the closing action this small valve seats first, avoiding any wire-drawing effect.
With double-cylinder engines two of these pumps are used, both suction valves being driven by the one cam rod while the two plungers are controlled by the single eccentric rod. To give the proper timing to the two suction valves, the fixed or suction cam has two flat spots. Both valves are opened and closed twice during each revolution. With each valve, one of the closures occurs when the pump plunger is on the suction stroke, and so no oil is injected during this particular valve closure.
Primm Oil Engine governor is of the con stant injection-angle type and is possessed of certain unique details. The assembly is shown in Fig. 314. The governor con sists of a governor hub F, which has a flange G forming the back side plate. About this hub is fitted the eccentric bushing H. The eccentric I has guides milled on its inner surface as a support for this bushing. To the eccentric is fitted a pin J which acts as a crank in moving the eccentric. The enlarged end of this crank pin, which is recessed into the front coverplate, is provided with a governor weight arm A. An additional weight arm is pivoted to a dummy pin K, which does not come into action. The sec ond weight merely balances the active weight. The crank pin D is equipped with a small pinion which engages a gear mounted on the governor hub.
In operation, the action is as follows: Any increase of speed causes both the weight arms to move outward. Since one weight arm is fastened to the pinion D which is part of the eccentric crank, already mentioned, the weight arm and crank may be regarded as one lever fulcrumed at the pinion tooth which is in mesh. Then the outward motion of the weight causes the crank to move inward, carrying the eccentric with it, thereby reducing the eccentricity. This change in eccentric throw reduces the fuel pump stroke. With the usual governor, the change in ec centricity would alter the injection point. To maintain this in jection point at a fixed value, the governor crank is set so that the eccentric receives an angular motion as well as a movement across the shaft. The angular motion corrects the defect of changing injection point, keeping it at a fixed value. The movement of the crank produces a rolling or angular motion at the fulcrum tooth. This is taken care of by the pinion. The pinion teeth remain in mesh at all points of the governor crank's displacement.