Fuel Valve By-pass.—Each fuel line has a by-pass, or relief valve, mounted on a block at the camshaft cover. Before the engine is turned over under air pressure, these valves should be opened and left in this position until a solid stream of oil issues from each valve, thus indicating that all air in the pump or oil lines has escaped. When running, frequently one or more cylin ders skip in firing, or.fail to fire at all; this, in most cases, is due to an air-bound fuel line.
McIntosh & Seymour fuel valve of this engine, appearing in Figs. 117 and 118, is contained in a cast-iron housing or cage. The valve, the needle end of which has a 60-degree included angle, seats on the cage itself. The upper end of the cage carries the spring housing. This end of the valve stem is screwed and locked into a dashpot, against which the spring bears. The valve is opened by the movement of the rocker arm shown. The atomizer is the detail of the valve that differen tiates it from other American fuel valves. This is a gun metal barrel, the diameters of which are of irregular dimensions. The interior is bored taper, fitting the valve stem at the upper end, while a number of passages connect this taper bore with the outside surface. In operation the charge of oil is forced, by the fuel pump, through the passage 0 and surrounds the atomizer at the space J, issuing through the serrated fins at K and L until the fuel reaches the level P, Fig: 119. The injection air fills the cavity above the atomizer, and, when the needle valve opens, this air flows through the ports B and along the valve stem into the cylinder. The air pressure on the surface of the oil at J remains constant while the velocity of the air current along the valve stem reduces the pressure at the inner end of the oil ports E. The consequence is a flow of oil through the oil ports E under the influence of the unbalanced air pressure. This oil, as it enters the stream of high-velocity air, is broken up and thoroughly atomized by the time it reaches the cylinder through the atomizer cap M. . The flow of oil continues until the oil level falls below the ports E. If the fuel valve is properly timed, the valve should then close, preventing an excessive amount of air blowing into the cylinder. Although this excess air may actually
increase the m.e.p. of the engine as figured .from an indicator card, it represents a loss of power since it has been compressed to 900 lbs. per sq. inch and is allowed to expand through the nozzle to 500 lbs. per sq. inch without doing any work.
On full load the closure of the needle valve should trap a small amount of oil immediately above the valve seat. This oil, on the next valve opening, is blown in ahead of the air charge, providing an initial ignition to balance the chilling action of the expanding air charge. It is variously claimed that an injector effect is set up by the air current. In reality, the action is merely that of unbalanced forces, and the oil below the ports E remains in the atomizer. The oil, if it contains dirt or a tarry base, gums badly until the fuel chamber is filled, forcing the oil to deposit around the valve stem. When this occurs, the oil enters the cylinder in a slug. This is indicated by loss of power and a smoky exhaust. The remedy is, of course, the cleansing of the atomizer.
It is claimed that this valve design permits operation with a lower injection air pressure than with other types of atomizers. In practice it would appear that this advantage does not exist as at full load a pressure of about 900 lbs. gage is necessary.
Adjustments—Valve Stem.—The valve stem, which is steel, corrodes with a sulphurized oil and must be burnished at each re moval. The stuffing-box is best packed with shredded babbitt, athough vulcanbestos is very serviceable. After the valve has been ground, it becomes necessary to bring the distance from the valve tip to the rocker lock washer back to the original length. This is accomplished by running both the washer and lock-nut up until there is the proper clearance between the fuel cam and rocker roller. The spring tension can be made normal by the insertion of a washer between the spring and the dashpot, or spring cap. The valve can be reground until the lock-nut is against the dash pot at which time a new valve must be secured.
Valve Cage.—The valve cage is held by two studs and rests on a taper seat in the cylinder head casting. This taper joint should be cleaned of soot before the cage is replaced or the joint will leak.