B. Power Transmission Through The Gears

1. It is important that you know how the power of the engine is transmitted through the gears to the drive sprocket. This knowledge is essential for locating many problems which would occur in a transmission of this type.

2. First, study the two photos of the transmission gears, Figures 31 and 32. Fig. 31 shows the correct location of the gears and gives the proper name for each part. Fig. 32 is the same picture, but a letter has been substituted for each gear name. This has been done to avoid confusion. In the following text, an explanation is given as to the exact function of each gear in the assembly. In some cases, this will involve repeating the name of a gear several times in one or two sentences. By using a letter to identify each gear, the explanation can be made much easier to understand.

3. Fig. 32 shows the gearbox in neutral. Notice that all the gears on the mainshaft are meshed squarely with those opposing them on the layshaft. At no time will any of these gears become unmeshed with its opposing gear, nor mesh with any other gear. Even when the sliding gears move back and forth to their farthest point, they will retain at least a 60% mesh with their opposing gear. This is why the gearbox is referred to as a "constant mesh" type.

4. Some gears on each shaft are locked to their respective shafts either by splines or by being made an integral part of the shaft. On Fig. 32, there is a printed "YES" or "NO" above the gears on the mainshaft and below
the gears on the layshaft. This denotes whether or not that particular gear is locked to its shaft. "YES" means it is, "NO" means it is not. Take note that if a gear is locked to the mainshaft, its opposing gear is not locked to the layshaft. This is an important point to remember as you learn about the power flow through the gears in the transmission.

5. 1st Gear: From the neutral position, the gearshift lever is pushed downward to engage 1st gear. When the selector shaft turns, the selector pawl pushes downward on one of the selector pins in the shift drum. This causes the drum to rotate counterclockwise, looking at the left end of the drum. The grooves are ground in the shift drum so that when this happens, the shift fork that is connected to gear I slides to the left. Gear I has four round engaging dogs protruding from its left side. Gear J has four oval slots cut into its right side. When gear I moves to the left, its pegs fit into the slots in gear J, engaging them together as in Fig. 33. The other shift forks do not move, but remain in their neutral position. The power enters the gearbox through the mainshaft, and because gear A is locked to the shaft, it transmits the power to gear J on the layshaft. J is not locked to the layshaft, but gear I is. Because I and J are now locked together, the layshaft turns. On the far right hand end of the layshaft is gear F. This gear is an integral part of the layshaft and therefore always turns at the same speed as the shaft. Its opposing gear is E, which is not locked to the mainshaft. The drive sprocket is also mounted

Page 21