Fig. 9. Cam Shaft
Main bearings run loose for any length of time will be found very hard to adjust as the jar which they are subjected to invariably pounds them off center which makes readjustment a very difficult task to accomplish with lasting effect. New main bearings in a motor should always be scraped to secure a perfect fit. A loose piston or connecting rod bearing will produce a sharp knock which can easily be determined from the dull thud produced by a loose main bearing. ([Fig. 9].) The cam shaft revolves on bearings and is usually located at the base of the cylinders on the left hand side looking toward the radiator and carries a set of cams for each cylinder. The cam pushes the valve open, and holds it in this position, while the piston travels the required number of degrees of the cycle or stroke.
The cam shaft is driven from the crank shaft usually through a set of timing gears, and operated at one-half the speed of the crank shaft in a four cycle motor, as a valve is only lifted once, while the crank shaft makes two revolutions or four strokes. The cam-shaft bearings, and the timing gears are usually self-lubricating and require very little attention. Timing of the cam shaft is a rather difficult matter and will be treated in a following [chapter] under the head of valve timing.
| Start Gear | Key-Seat |
| Shaft-Seat | |
| Cone Clutch Seat | Disc Clutch Small Disc Bolt on Here |
Fig. 10. Flywheel
The oil pan or reservoir forms the lower half or base of the crank case. The lubricating oil is carried here at a level which will allow the piston rods to dip into it at each revolution of the crank shaft. The timing gears receive their lubrication from the supply carried in the reservoir by means of a plunger or piston pump which is operated from the cam shaft. The balance of the motor is usually lubricated by a splash system taken up in a later [chapter] on lubrication. The oil is carried at a level between two points marked, high and low, on a glass or float gauge which is located on the crank case. A gasket made of paper or fiber is used between the union or connection of the oil reservoir and the upper half of the crank case to prevent the oil from working out through the connection.
[Fig. 10] represents the flywheel. The flywheel is usually keyed to the crank shaft directly behind the rear main bearing. This wheel is proportionate in weight to the revolving speed of the motor, which it keeps in balance by gathering the force of the power stroke. The momentum gathered by it in this stroke carries the pistons through the three succeeding strokes called the exhaust, intake, and compression strokes. The flywheel also serves as a connection between the power-plant and the running gear of the car, as a part of the clutch is located on it, and the connection takes place either in the rim or on the flange.
CHAPTER II
VALVE CONSTRUCTION, TYPES, AND OPERATION
The proper and accurate functional operation of the valves is as necessary to successful motor operation as the proper adjustment of a hairspring is to a watch, for if a hairspring becomes impaired in any way, a watch will not keep correct time. This is the case in a motor when a valve becomes impaired. The valves in a motor, therefore, must be considered the most vital part conducive to successful and economical operation of the motor.