An “opposed” type engine is in the most perfect mechanical balance of any engine as the crank shafts and connecting rods are not only on opposite sides of the crank-shaft, but make equal angles with the center line of the cylinders as well, at all points in the revolution. The explosive impulses occur at equal angles in the revolution as in the four and six cylinder vertical type. An opposed engine may be considered as a “V” having a cylinder angle of 180°. In the opposed type, one crank throw is provided for each cylinder, the pistons of the opposite cylinders traveling in opposite directions at the same time.
A “radial” or “Fan” type motor, as the name would suggest has the cylinders arranged in one or two rows around the crank case, each cylinder being on a radial line passing through the center of the cylinder with one crank throw for each row. The Gnome engine illustrated elsewhere in the book is an example of this type, the seven equally spaced cylinders acting on a common crank throw. When more than seven cylinders are used on this engine, as in the fourteen cylinder engine, two cranks are provided, each crank serving seven cylinders. This arrangement cuts down the weight of a motor enormously because of the short crank shaft and case. With the ignition properly timed and the cylinders correctly spaced the firing impulses occur at equal angles.
“Tandem” cylinders are employed only on stationary engines, the cylinders being placed on the same center line, one in front of the other, and when this arrangement is adopted it is the usual practice to make the cylinders double acting. The two pistons are connected by a rod known as the “piston rod” which extends from the rear end of one cylinder into the front of the following cylinder. Tandem cylinders require too much room for use on automobiles or motor boats, and for this reason are seldom seen in this service.
The “twin” engine is a modification of the vertical cylinder arrangement, both cylinders being on the same side of the shaft and in line with one another. It is the type most generally used on very large stationary engines that have more than one cylinder, and instead of being vertical as in their prototype are generally laid horizontally. Since the twin engine is generally double acting, the crank throws are placed on opposite sides of the shaft.
(45) Four Cylinder Vertical Auto Motor.
A common type of four cylinder vertical motor is shown by Fig. 19, which is of the type commonly used on automobiles. In order to show the general construction of the cylinder, each cylinder is cut through at a different point. The cylinder at the extreme left is shown in elevation, or as we would see it from the outside. In the second cylinder from the left, the section is taken through the valve chamber, which projects from the side of the cylinder. A section through the center of the cylinder is shown on the third cylinder, and the fourth cylinder is in elevation.
On cylinder No. 1, (left) is seen the exhaust pipe (32) and the inlet pipe (31) entering to valve chamber and connected to the exhaust valve and inlet valve respectively. The pipes are held in place by the clamp or “crab” (33). The exhaust pipe connects with the exhaust valve of each cylinder, and terminates at the fourth cylinder as shown by (32). Screwed into the top of the valve chamber on cylinder No. 1 are the two spark plugs (34) and the relief cock (35).
Referring to cylinder No. 2, the inlet valve (42) is shown at the left of the chamber and the exhaust valve also shown by (42) is shown at the right. Above the valves are the spark plugs (34) which project into the space above the valves. Pressing against the lower ends of the valve stems and holding the valves tight on their seats are the springs (44) which fit into the washers (45) fastened to the stems. The valve stems terminate in a nut at (48). The valve stem guides (43) form a support for the valves and at the same time form an air tight connection for the stems to slide in.
Immediately beneath the stems are the push rods (46) which are provided with an adjustment (48) at the upper end, and a roller (49) at the lower end. The rollers (49) rest directly on the cams mounted on the cam shaft (27), and as the irregular cams revolve, the push rods are moved up and down which in turn act on the valve stems and raise the valves at the proper moment. The cams raise the valves and the springs close them. The two cams (exhaust and inlet) appear as two rectangular enlargements on the shaft (27). The bearings (53), support the cam shaft, one being supplied for each cylinder.
At the extreme left of the crank shaft is shown the half time gear (20) which meshes with the gear on the crank-shaft and drives the cams. Next to this gear is the large cam shaft bearing 26. It should be noted that the section through the valve chamber taken on cylinder No. 2 is at a point considerably back from the center line of the cylinders and not in the same plane as the section shown on cylinder No. 3, which is taken through the center line of the cylinders.