CHAPTER I
GAS ENGINE CONSTRUCTION, AND PARTS
We will use for purposes of illustration the common four-cylinder, four cycle, cast en bloc, “L”-head type of motor, as this type is used probably by 90% of the automobile manufacturers. The block of this type of motor is cast with an overlapping shoulder at the upper left hand side which contains a compartment adjoining the combustion chamber in which the intake and exhaust valves seat, and the casting is made, in the shape of the Capital letter L turned upside down. This arrangement allows both valves to seat in one chamber and to operate from one cam shaft.
The operation of each cylinder is identically the same whether you have a one or a many cylindered motor, consequently when you have gained a working knowledge of one cylinder, others are a mere addition. This may sound confusing when the eight or twelve cylindered motor is mentioned, but is more readily understood when we consider the fact that an eight or twelve cylindered motor is nothing more than two fours or two sixes, set to a single crank-case or base in V-shape to allow the connecting rods of each motor to operate on a single crank shaft. This arrangement also allows all the valves to operate from a single cam shaft, thereby making the motor very rigid and compact, which is an absolute necessity considering the small space that is allowed for the motor in our present-day designs.
[Fig. 1]. The casting or block, which is the foundation of the whole motor or engine, usually has a removable head which allows for easy access to the pistons and valves. The block is cast with a passage or compartment through the head and around the cylinders through which water circulates for cooling the adjoining surfaces of the cylinders. This alleviates the danger from expansion and contraction caused by the tremendous heat generated in and about the combustion chambers. This block also contains the cylinders and valve seats. The pistons and valves are fitted to their respective positions as construction progresses.
| Det. Head | |
| Exhaust Pt. Intake Pt. Re. Plate | Cyl. Block |
| Upper Crankcase | |
| Lower Crankcase |
Fig. 1. Typical Four-cylinder Block
[Fig. 2]. The block with head removed shows the smooth flush surface of the block face and the location of the cylinders in which the pistons operate or slide, with each power impulse or explosion. When the piston is at its upper extreme it comes within a sixteenth of an inch of being flush with the top of the block, while the valves (also shown in Fig. 2) rest on ground-in seats, in their respective chambers, and are operated by a stem which extends downward from the head through a guide bushing in the block to the cam shaft.
Pistons
Water Vents
Intake Valve
Exhaust Valve