Fig. 4. Typical Cylinder Piston
[Fig. 4A] shows a split piston. Three grooves are cut into it near the head to receive the piston rings. The width and depth of these grooves vary according to the size of the piston. A hole is bored through the piston and shoulders about half way from each end. The bushing or plain bearing shown in [Fig. 4B] is pressed into this hole and forms a bearing for the wrist pin also shown in [Fig. 4B]. Wrist pins are usually made of a much softer metal than the bearing, and are subjected to severe duty, which often causes them to wear and produce a sharp knock; this may be remedied by pressing out the pin, giving it a quarter turn, and replacing it in that position.
Fig. 5. Typical Piston Ring
[Fig. 5] shows a split joint piston ring. Piston rings are usually made from a high grade gray iron, which fits into the grooves in the piston and springs out against the cylinder walls, thereby preventing the compressed charge of gas from escaping down the cylinder, between the wall and the piston. [Fig. 5A] shows a piston equipped with leak-proof rings; this type of piston ring has overlapping joints, and gives excellent service, especially when used on a motor which has seen considerable service. [Fig. 5B] illustrates how piston rings may line up, or become worn from long use, or from faulty lubrication. This trouble may be easily detected by turning the motor over slowly. The escaping charge can usually be heard and the strength required to turn the motor will be found much less uniform on the defective cylinder.
The motor should be overhauled at least once every year, and by applying new rings to the pistons at this time new life and snappiness may be perceived at once.
The connecting rod shown in [Fig. 6] has a detachable or split bearing on the large end, and takes its bearing on the crank pin of the crank shaft. The small or upper end may have either a hinge joint or press fit to the wrist pin. This rod serves as a connection and delivers the power stroke from the piston to the crank shaft. These rods are required to stand very hard jars caused by the explosion taking place over the piston head. The bearings are provided with shims between the upper and lower half for adjusting. Piston or connecting rod bearings must be kept perfectly adjusted to prevent the bearings from cracking or splitting which will cause the rod to break and which may cause considerable damage to the crank case.
| Wrist Pin Bearing | Upper Half Crank Pin Bearing | Lower Half Bearing End Overlaps |
| Shims | ||
| Bolts | ||
| BushingRod | Shims | |
Fig. 6. Typical Connecting Rod