Page:Ford manual 1919.djvu/9



Gasoline when mixed with air and compressed is highly explosive. An explosion in a violent expansion caused by instantaneous combustion of conﬁned gases. In the gasoline engine the mixture is drawn into a cylinder, where it is compressed by an advancing piston and then exploded by an electric spark, which sends the piston downward, and through the connecting rod imparts a rotary motion to the crankshaft. (See Cut No. 2.)

On the downward stroke the suction of the piston draws the fresh gas from the carburetor, through the inlet pipe and valve, into the cylinder. The upward movement of the piston compresses the gas into a very small space, between the top of the piston and the depression in the cylinder head, known as the "combustion chamber." (The compressed gases exert a pressure of approximately 60 pounds per square inch.) At this point the electric spark, generated by the magneto, explodes the gases—driving the piston downward—thus producing the power which turns the crank shaft. On the next stroke upward the piston drives the exploded gas out through the exhaust valve and pipe to the muffler. (See Cut No. 3.)

It is a steel rod, connecting piston and crank shaft. Should the babbitt bearing become worn, or burned out through lack of oil, a knocking in the engine will result—in which case the entire connecting rod should be replaced. To make this replacement, (1) drain oil from crank case; (2) take off cylinder head; (3) remove detachable plate on bottom of crank case; 4) disconnect connecting rod from crank shaft; (5) take piston and rod out through top of cylinder.

One intake and one exhaust valve are located in each cylinder. The former admits the fresh gas drawn from the carburetor through the inlet pipe—the latter permits the exploded gas to be driven out through the exhaust pipe. The valves are alternately opened and closed (see Cut No. 3) by the cams on the cam shaft striking against push rods which in turn lift the valves from their seats.

In timing the engine the points of opening and closing of the valves are, of course, what should be considered. As the valves are properly timed at the factory when the engine is built the necessity for retiming would occur only when such parts as the cam shaft, time gears or valves were removed in overhauling the engine.

In fitting the large time gear to the cam shaft it is important to see that the first cam points in a direction opposite to the zero mark (see Cut No. 3). The time gears must also mesh so that the tooth marked zero (0) on the small time gear will come between the two teeth on the large gear at the zero point. The time gears [9]