Bottom End The purpose of the bottom end is to facilitate the transfer of energy from the top end (where is it produced) and move it towards the wheels at the desired rate. It does this using the parts shown above in the picture. The purpose of the transmission is to take in a certain narrow input on the main shaft and convert it into a wider range of outputs to produce different speeds. It does this by engaging different gears to produce a different output:input ratio, which will be reviewed in the next couple of slides. The cam plate pictured here dictates which gears are engaged, because the forks that determine the positions of the locking gears have rollers that sit inside the horizontal channels in the cam plate and take different positions as the plate is rotated by the shifter. This photograph shows the gears in a standard ratio transmission, along with the number of teeth on each gear. 1st gear produces an output:input ratio of 0.33 (in other words, for each full turn of the output sprocket, the input must complete 3 full turns). This is the lowest speed on the motorcycle. The engaged gears are shown in red. In neutral, none of the gears are engaged, which allows the engine to turn freely without producing any output (i.e., without spinning the wheels). 2nd gear produces an output:input ratio of 0.49, which enables the motorcycle to attain higher speeds than first gear. 3rd gear has an output:input ratio of 0.75, which enables it to reach even higher speeds. 4th gear does not engage any of the gears in the lay shaft, and therefore produces an output:input ratio of 1:1. This gear corresponds to the highest speeds that the motorcycle can achieve. We noticed that parts of the engine cover had been worn away, which led us to believe that in the past, the motorcycle was run with a loose chain (chains can stretch due to wear and heating) that rubbed continuously against the case and wore away the material. The subsequent holes were problematic, as they would lead to severe oil leakages if left. To solve this problem, we replaced the chain and built a tensioner, using CAD and then a CNC machine, to keep the chain from hitting the side of the case if it ever became loose. The screw attached to the tensioner can be moved up and down in order to adjust the tension in the chain, ensuring it stays away from the cover even as it stretches more and requires the tensioner to take up more slack. Bottom-End