In event the pump refuses to deliver oil to the cylinder, the pump cam should be inspected. It is split, being held by a clamp bolt, and is liable to slip. The hammer blow due to the sudden movement of the pump plunger causes the plunger roller to chatter against the cam face, leaving a series of ridges. To eliminate this, the builders have tried an inlay of tool steel at the nose or high point; and have used an all tool-steel cam. It would appear that, in cam construction, the cam nose only should be of oil-treated, high-carbon steel, while the body of the _cam should be of cast steel or machinery steel to absorb the shocks.
Adjustments of the Fuel is called to the starting lever M, Fig. 298, which is fulcrumed on the pump housing and, in starting, is used to pump the fuel by hand to one cylinder. A few strokes usually fill the discharge pipe. When this is accomplished, the handle is set to the neutral position until the air starter is cut out. In stopping a multi-cylinder engine the by-passes on all except this one cylinder is opened, preventing any explosions in these cylinders. The pump handle is then slowly drawn back so that the fuel to this one cylinder is gradually reduced. If the fuel is shut off instantaneously, the engine will pound very violently.
Another important detail is the by-pass valve N. Usually, in starting, the engine has a tendency to take too heavy fuel charges because the governor arms are at their innermost position and the movable cam at its most advanced point so that all the fuel entering the pump chamber must pass through the discharge valve into the cylinder. To overcome this objection, the by-pass valve N is provided. In starting, the operator opens the valve a slight amount, thus allowing part of the charge to flow back into the suction line. Under ordinary conditions, when the engine runs only partially loaded, it is advisable to " crack " the valve and by-pass part of the fuel. This causes the governor to advance the suction valve cam so that the charge is forced into the cylinder earlier than when the by-pass is not used on low loads. The result is a greater time interval for the fuel to vaporize and burn, and better combustion is obtained. Where the engine is a multi cylinder one, adjusting the by-pass valve serves to equalize the fuel charges to the different cylinders. It is impossible to secure exact distribution by adjustment of the suction valve tappet rods.
The suction valve and discharge valve are of the spring-loaded, poppet type, and in regrinding the utmost care must be exercised. It is unnecessary to grind the valve so that the entire seat is in perfect contact. A line contact inch in width is very satis factory and will usually be better than a poor job of grinding the entire seat into contact. While the erecting engineer may in
struct the operator to use powdered glass as the grinding medium, a fine grade of emery flour and oil has made an excellent job on numerous occasions.
When heavy fuel or boiler oil is used unfiltered, the grit carried with the oil will cut the pump valves rather rapidly, even though the engine, at all times, employs a small oil filter, which is located immediately above the pump. Ordinarily, such oil is thick enough to be sluggish about leaking past the valves. However, if a change is made to an oil of lighter gravity, such as distillate oil, the valves will leak badly, since this oil will seep by a valve showing the slightest ridge or rough spot on its face. If, after making a change in the oil, the engine seems to lose power, the. new oil should not be the subject of censure, but the condition of the pump valves should be investigated. This, of course, applies to any and all makes of fuel pumps.
If the engine is of fair size—above 100 h.p.—and the lower cost of the unfiltered fuel oil is attractive, the operator should prepare to meet these valve leaks. It is a good plan to procure a valve-seat reamer so that the seat may be brought back to its proper shape when badly scored. Since the valve seat is of brass, a reamer of ordinary tool steel, hardened, will do good work. The reamer should be in the shape of a cone with a number of cutting edges or notches, and the sides of the cone should have a 45 degree slope to conform to the angle of the valve seat.
After regrinding or reaming a valve seat, it is imperative that the outer end of the valve plunger or tappet rod be adjusted to give the proper clearance between valve stem and tappet rod.
Mietz and Weiss 301 outlines the governor of the single- and two-cylinder horizontal Mietz and Weiss oil engines. The governor consists of a weight arm A, which is pivoted to the flywheel by the pin B. This arm, by means of a pin connection D, moves the eccentric along the governor slide, which is fastened to the crankshaft. As the engine speeds up, the weight arm tends to fly outward, moving the eccentric along the governor block. This shortens the throw of the eccentric, which in turn reduces the pump plunger stroke. In order to secure stability of the arm, the centrifugal force is opposed by the tension in the governor spring. This method of changing the eccentricity by means of the sliding governor block is somewhat similar to the Muncie governor, and the same results are achieved— variations in both pump stroke and injection angle, or angle of advance.