The valves are manufactured from a high grade tungsten or carbon steel, and are designed to withstand the intense heat which the heads located in the combustion chambers are subjected to, without warping. A perfect seat is required to prevent leaking, which will cause low compression and a weak power impulse, thus reducing the power and harmony of successful operation.
The poppet valve is used by about ninety-five per cent. of motor manufacturers. This type of valve is mechanically operated from the cam shaft at one-half the crank shaft speed, as a valve is lifted only once in every four strokes, or two revolutions of the crank shaft. The reduction in speed is accomplished by using a gear on the cam shaft, twice the size of that on the crank shaft.
The heads and chambers must be kept free from carbon which forms and bakes into a shale and has a tendency to crack and chip as the temperature changes in the combustion chambers. These chips are blown about in the cylinders until they lodge or are trapped by the descending valves. It then forms a pit on the seat and prevents the valves from seating properly. This leaves an open space which attracts more carbon, and the entire functional action of the valve is soon impaired, necessitating regrinding in order that it may properly seat again.
Carbon is generated from a poor gas mixture or from excessive use of lubricating oil and may be considered the chief cause of improper functional action of the valves.
VALVE CONSTRUCTION, TYPES, AND OPERATION 8-CYLINDERED V-TYPE ENGINE
| Valve Head | Removable Plates | Cam Shaft | Valve Head |
| Valve Seat | Valve Seat | ||
| Tappet for Adjusting Valves | Tappet for Adjusting Valves | ||
Fig. 11. 8-Cylinder Valve Arrangement
[Fig. 11] shows the location of the cam shaft, valves, and tappet adjustment, on a V-shaped engine. The cylinders of this type of engine are arranged in two blocks, consisting of four cylinders in each, set directly opposite each other on an angle of 90°. The connecting rods from opposite cylinders are yoked and take their bearing on the same crank pin. This arrangement allows the intake and exhaust valves of each opposite cylinder to operate from a single cam shaft, or in other words the entire sixteen valves are operated by a single cam shaft carrying eight cams. Consequently an eight or twelve cylindered engine is identical in regard to valve timing to either a four or six cylindered engine.
