Fig. 10.—Connecting Rod Bearings
Fig. 11.—Piston Complete and in Section
The piston is attached to the crank shaft by a connecting rod, which is illustrated in [Figure 10]. Pistons are shown in [Figures 11] and [12]; they are made as light as is consistent with the pressure that they must bear, and are hollow, and open at the lower end.
The piston is attached to the connecting rod by a wrist pin, or piston pin, which is a shaft passing through it from side to side, and also through the bearing in the upper end of the connecting rod. The connecting rod swings on the wrist pin in following the rotation of the crank shaft, and its attachment to the wrist pin must permit this without being loose.
The bearings at the two ends of a connecting rod are usually adjustable, so that wear can be taken up; some of the methods of doing this are illustrated in [Figure 10]. In A, the wrist pin bearing is a plain tube, ground to an exact fit; when it is worn it must be replaced. In B, the bearing is split, and the ends are drawn together by a bolt to the correct fit. The bearing in C is in two parts, held together by a U-shaped bolt, while in D the two parts are held together by a cap bolted to the end of the connecting rod. In E, the end of the connecting rod is a square loop enclosing the two parts of the bearing; the parts are held in the proper position by a wedge adjusted by screws.
The crank shaft bearing of the connecting rod [shown in F] is in two parts which are hinged together. G, H, and K show the forms usually used in tractor engines, which consist of two parts bolted together.
Fig. 12.—Wrist Pin Fastenings