The lost motion in all parts of an engine should be taken up frequently, to keep it running smoothly, but care must be taken not to tighten bearings or keys too tight.
A. Lap is the position of the valve which extends or laps over the edge of the ports when the valve is in its central position. That on the inside of the D is the inside or exhaust lap, while that at the ends of the valve is the outside lap and affects the admission and cut-off.
Lead is the amount of opening which is given to the port by the valve when the engine is on the center.
Lead on a valve is the admission of steam into the cylinder before the piston completes its stroke.
A. There is no general rule for the amount of lead that would be best suited for all makes of engines. It must be determined by the design or construction, speed and work required, to produce the best results for economy and quietness in running.
A. A throttle engine is one in which the speed is controlled by throttling the steam with a governor, as opposed to an automatic engine in which the speed is regulated by varying the point of cut-off at the valve.
Q. What is the difference between a stroke and a revolution?
A. A stroke is the movement of the piston, from one end to the other of cylinder. A revolution takes two strokes of piston.
Q. How are steam packing rings put on the piston head?
A. Remove the back cylinder head and take the piston and rod out of the cylinder, and stand it “head up.” Then place the inside of the ring, opposite to the opening, against the side of the piston head next to you; gradually press the ring open with your hands, and it can be easily slipped over the head and put in place.
A. It is always entered from the back end in horizontal engines. The rings (if steam packing) should be carefully placed in position and compressed by the hand if piston is small, but if large, curved blocks of wood or a band of sheet iron can be used to support them until they enter cylinder. When the piston rod passes through the stuffing box, it should be supported at outer end to prevent cutting.
The frame of this engine is very heavy, with longitudinal and cross ribs securely bracing it. It forms the lower guide for cross-head, and contains the pillow block bearings at the front end. It also forms the front cylinder head, to which the cylinder is bolted. The working parts are placed as low in the frame as is possible, so that the strain is brought in line with the line of greatest resistance.