Fuel layshaft is provided with a hub disk which is held by a nose-key. This hub is fitted with an extension upon which is keyed the air-starting cam. The hub flange, as will be observed in Fig. 127, is slotted. Into these slots are placed the fuel cam bolts. The fuel cam also appears in Fig. 126, where it can be seen that it has an adjustable nose. In set ting the fuel valve timing, the fuel cam can be moved several degrees around the hub disks and held in place by the bolts. This provides the easiest method of adjusting the fuel valve timing.
The National Transit Diesel Fuel Valve.—The National Transit Co. equip their Diesels with an open-nozzle fuel valve, Fig. 128. The needle valve is placed vertically in the valve block and has the closing spring located in the top of the valve body. This spring is enclosed in a sleeve which is in contact with the needle 'vallie and is tnoved Vertically, 'compress. ing the spring, as the valve is opened by the rocker.' The oil enters the valve passage of the atomizer through the check valve a. The oil reservoir extends the depth of the cylinder head. This causes the oil charge to spread out in a thin sheet; consequently, the'air does not pick up the oil in Owing to this passage length; no atomizer disks are necessary: The valve body has no cooling water passages since it rests in a thin bushing pressed into the cylinder head; the cooling effect through the bushing is quite satisfactory.
The fuel valve of the National Transit Diesel manufactured prior to 1918 was opened by a push-rod carried in the hollow housing of the camshaft end bearing. This push-rod is in con tact with the fuel cam, Fig. 13, Chapter II.
On later Diesels the fuel valves are driven from the camshaft in front of the cylinder, as appears in Fig. 128. The fuel valve and starting valve rocker are here mounted on an eccentric which is machined on the fulcrum shaft. In starting, a lever gives an angular displacement to the fulcrum shaft; this shifts the eccen tric, throwing the fuel valve rocker away from the valve stem and moving the air starter rocker into position.
Fuel Valve timing the valve opening and closure the adjusting nut on the valve stem is set to contact with the fuel cam at the desired piston angle for valve opening, as with practically all engines. The cam nose can be shifted to give the required closure. The spring cap must be in contact with the needle valve body at all times. After the valve is reground a few times the cap, or bushing, fails to touch the valve. To overcome this trouble the bushing should be ground off at the surface where it seats on the valve body at B. This has the effect of lowering the cap, causing it to again touch the valve.
Standard Fuel Oil Engine Fuel fuel valve of this engine is of the open-nozzle type. The valve is housed in a cast-iron bracket block and consists, in the main, of the steel valve body, atomizer, needle valve, fuel check valve, and valve actu ating spring and rocker, Fig. 129.
The operation is as follows: The charge of fuel, flowing through the pipe a and the check valve, enters the atomizer through the small port holes B. The air enters at the side of the valve block, passing around the valve stem above the seat at C. As the needle valve is raised, this air enters the atomizer passage D; to do this, the air must pass through the atomizer cone shown in the section B–B. This effectually breaks up the air stream, preventing the air from "slugging" the oil into the cylinder. As the high-velocity air passes over the oil, the latter is picked up and swept into the cylinder. As a means of giving sensitive control of the fuel supply on low loads and of eliminating " hunting " by the governor, a by-pass fuel valve is placed in the fuel line. When low loads are carried, the governor, which is of the Rites Interia type, is at the extreme limit of its travel.
In this condition this type of governor is unstable and will hunt excessively. By cracking the overflow valve to allow part of the fuel pumped to by-pass back to the tank, the governor is compelled to handle more than the engine's require ments. The governor then moves outward to a more stable position, giving a closer regulation to the engine speed.
Fuel Valve Actuating Mechanism.— The fuel valve is operated by a unique cam arrangement radically different from that used on all other Diesels. The device appears in Fig. 130 where a, the fuel valve, is moved by the dog b; this dog, in turn, receives its motion from the cam lever d. On ro Drag Crank the lower end of this lever is mounted a roller which is in con tact with the cam e. It will be observed that, as the engine turns over, the drag crank, being connected to the reach-rod and crank f, will raise the needle valve through this system of levers. The cam nose comes under the roller twice in each revolution of the engine, and, since the engine is a two-stroke-cycle, it then becomes necessary to pro vide some means whereby the roller is raised only once per revolution of the engine shaft. This is accomplished by equip ping the cam roller with two flanges, as more fully illustrated in Fig. 131. The can is milled with curved sides, and the nose extends over only one-half of the cam width. As the reach-rod moves to the left, Fig. 131, the right-hand roller flange bears against the earn edge; the cam nose then passes between the flange and the roller. At the extreme travel of the reach-rod, the curved side of the cam throws the roller to the left, pulling it into the position a, Fig. 131. When the drag crank reverses the travel of the reach-rod f, the cam nose strikes the roller, raising the needle valve; the cam at the end of its travel then shifts the roller to the right to the position b, which allows the roller on the return stroke to slide over the cam, untouched by the nose.