Fig. 16. Knight Valve-Timing Marks—8-Cylinder
VALVE CONSTRUCTION
If the sleeve rods are removed for some reason, the bearings should be fitted very loosely to the eccentric shaft when they are put back. A looseness of about .008 of an inch is permissible.
CHAPTER III
THE OPERATION OF A 4-CYCLE, 4-CYLINDERED ENGINE
The four-cycle or Otto stroke type of gasoline engine should rightly be called the four-stroke-cycle engine, as it requires four strokes and two revolutions of the crank shaft to complete one cycle of operation.
This type of motor is used almost universally by the manufacturers of pleasure cars due to its reliability, and to the ability it has to furnish continuous power at all speeds with the minimum amount of vibration.
| Firing Stroke | Exhaust Stroke | Intake Stroke | Compression Stroke |
| 1 | 2 | 3 | 4 |
Fig. 17. 4-Stroke Cycle. 1—Cylinder in Action
[Fig. 17] shows a diagram of one cylinder in the four strokes of the cycle, and the distance traveled by the crank shaft during each stroke. No. 1 begins with a charge of compressed vapor gas in the cylinder and is called the firing or power stroke. The ignition system (explained in a later chapter) furnishes a spark at from five to fifteen degrees early or before the piston reaches top dead center. Although the stroke theoretically starts before the piston reaches its highest point of ascent, the actual pressure or force of the explosion is not exerted until the piston has crossed dead center. This is due to the fact that the piston travels very rapidly, and that it requires a small fraction of a second for spark to ignite the compressed charge of gas. It may, therefore, be easily seen that, if the spark did not occur until the piston is on or has crossed dead center, the piston would have traveled part of the distance of the stroke, and as it is moving away from the highest point of compression the pressure is reduced by allowing more volume space which causes a weak explosion and a short power stroke. The intake and exhaust valves are closed through the duration of the power stroke.