The YZ125 engine provides a workhorse power source for Yamaha off-road motorcycles. Unlike more modern motorcycle designs, the YZ125 uses a two-stroke cycle assembly, making it easier to work on and install into a motorcycle frame. As a result, the engine tends to be widely used in both off-road and road motorcycle assemblies. Like most engines, its installation process involves simple steps with basic garage tools. However, its the electrical and fuel connections that make the process a bit more complicated.
Instructions
- 1
Position the motorcycle frame on a motorcycle stand if its not already held up by similar equipment. Place the fully-assembled YZ125 engine next to the motorcycle frame, reducing the distance you have to travel with the engine block.
2Spread out all wiring, fuel lines and cable connections from the motorcycle frame so they are clearly visible before beginning installation. Position the engine block underneath the motorcycle frame.
3Locate the two engine block securing bolts (front and back). Grease the body of these bolts by hand but leave the securing threads of the bolts dry. Use lithium engine grease for the application. Wipe off any excess with a rag.
4Lift the engine block and line up the front swing arm with the motorcycle frame sockets. Insert the larger, front bolt through the frame and engine sockets until it pokes out the other side. Slip on the securing nut. Repeat the process for the rear engine connection with the second, smaller rear bolt.
5Use a socket wrench and crescent wrench to tighten the two bolts so the engine is secure in the motorcycle frame.
6Connect the electrical from the engine flywheel assembly, matching each of the colored wires to those coming from the motorcycle frame. Use a crescent wrench to connect the intake manifold and carburetor assembly to the top of the engine block. Finish the installation by attaching the rear-wheel-drive chain to the engine.
