Modification and conversion work of converting road-going motorcycle to suit off-road usage

Abstract

This project involves the real work of converting road-going motorcycle (Yamaha RXZ135 2-stroke) into a suitable motorcycle for off-road usage. Study was made on motorcycle to determine the modification to be carried out. The modification and conversion work was focused on maximizing the output torque and acceleration of the motorcycle for off-road usage, which will be used mainly in hilly and muddy terrains. Main scope of this project was the modification of the secondary drive system (chain drive system). This includes the design and fabrication of sprockets to suit the Yamaha RXZ135 motorcycle. As the size of sprocket needed is determined, design of sprocket was proceed, and fabrication was carried out by using CNC milling and Wire- EDM cutting machine. High precision and quality sprockets are fabricated for the modification. These sprockets are fabricated using Aluminum Alloy 6061 T6 which is light weight and has good mechanical properties. Fabricated sprockets were found fit well with the Yamaha RXZ135 motorcycle and the corresponding roller chain. With such modification, motorcycle gained a great increase of its output torque and acceleration, but at the mean time, the overall top speed of motorcycle had been sacrificed. Results of analysis show that by changing the front sprocket from 16T to 11T and rear sprocket from 40T to 52T, the motorcycle able to gain an increment in output torque as high as 89.09%. The theoretical maximum output torque of modified motorcycle which occurs during the 1st transmission speed is 242.402Nm. The total fabrication cost for sprockets were RM 1215.65, which the price is actually acceptable if compared to the market price.