ENGINE FRAMES. BEARINGS. SHAFTS. FLYWHEELS.
Engine the matter of frame design, each engine builder has followed his own ideas. Unlike steam engine manu facturers, hardly any two low-pressure-engine builders use the same design of frame. However, all may be separated into two types—the open frame, where the scavenging air is compressed in the front end of the cylinder; and the inclosed frame, where the air-tight frame itself serves as the air compreisor. Figure 256 is a view of an open-frame while Fig. 251 is a cross-section of an inclosed-frame engine. While both show a horizontal engine, it is in the vertical type engine that the inclosed frame is used exclu sively. This is for the reason that an open frame with cylinder air compression would make the engine much higher than is desirable.
Inclosed inclosed frame is immensely attractive both from a manufacturing and an operating viewpoint. Since all parts are bound together the frame can weigh less for the same strength. Being inclosed, the matter of keeping the bearings and cylinder free from grit is very much simplified. However, of late, a number of open-frame engines are being equipped with dust-proof steel covers. Many engines of the horizontal two stroke-cycle type have frames that are entirely inclosed, access to the interior parts being had only by a small opening at the front of the frame. This opening is taken up by the air-check valve, and inspection of the parts involves removal of the valve and the suction piping. In an engine of this design the engineer should not fall into the lamentable habit of neglecting to inspect the connecting-rod brasses. It is not easy to do this, but even though it does involve considerable effort the air valve should be removed at least monthly, and the crank box inspected for wear. There is a tendency at all times for this bearing to wear unevenly, allowing the rod to get out of line, and it is more likely to happen in the inclosed engine if the engineer is lax in his inspection.
Another detail of importance, especially in the horizontal en gine, is the necessity of keeping the crankcase free from excess lubricating oil. In many plants the engineer is careless in this
matter and allows the oil to accumulate until the crank strikes the oil surface. This causes the oil to splash into the piston and also causes the air to be charged with a fog of lubricating oil particles. This fog of lubricating oil is blown along with the air into the cylinder at the moment the air port is opened. These particles blow on out through the exhaust, giving it a decidedly smoky appearance. The oil which splashes into the piston may strike the hot piston head, carbonize and adhere in a thick coat or scale. Means of removing the heat from the piston head are meager at the best, and scale is a poor conductor of heat. There fore, this splashing oil will likely contribute to a fractured piston head. In the vertical cylinder this carbonized scale on the in terior of the piston has a habit of dropping down on the crank pin and piston-pin brasses. Small particles working in between the pin and brass cause a good many hot boxes. The splashing lubricating oil, in a horizontal engine, strikes the cylinder walls in excessive amounts. This oil will invariably gum up the piston rings and frequently cut the piston. Figure 272 is a cross-section of the Mietz and Weiss engine which uses the inclosed frame; the Fairbanks-Morse inclosed frame appears in Fig. 253.
Engines using the front end of the cylinder as the air com pressor are free from those troubles due to the oil in the crank case. The crankcase, in such designs, is entirely separated from the air chamber. As a result of this separation, quite a number of these engines use a splash-oiling system for the lubrication of the crank pin and main bearings. This gives a copious supply of oil to these parts. The oil, however, should be removed oc casionally for refiltering. When the runs are long, the oil should be drawn off and cool oil substituted. It does not require many days of operation to raise the oil temperature up to a point where the lubrication of the pin becomes unsatisfactory. Figure 255 is a cross-section of the Bessemer engine, which uses the splash oiling system.