Q. What is a half stroke?
A. It is the point reached by the piston after traveling exactly one-half its travel.
Q. What is the meaning of “lost motion”?
A. Lost motion is looseness of the connecting rod at crank or wrist-pin, or looseness of the link or link block, cross-head and guides, main crank shaft and pillow block, caused by friction and wearing away of the metals and the neglect to take up the wear.
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.
Q. What is lap and lead?
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.