Yamaha Motor Co., Ltd. 5CU-11631-00-B0 Piston

The Yamaha 5CU-11631-00-B0 piston is a genuine OEM standard-bore replacement designed for two-stroke motorcycle engines, most notably the Yamaha YZ250 models from 1999 and 2000. It features an approximate 66.36 mm bore and aluminum alloy piston construction for effective heat dissipation, with mounting to the connecting rod via a wrist pin to form a core engine component in the crankshaft-piston assembly. This piston is used in motocross and racing engines requiring precise fit, durability, and efficient combustion in high-performance setups. OEM part number 5CU-11631-00-B0, with common replacements including 5CU-11631-00-A0, 5MW-11631-00-B0, and 5NX-11631-00-B0.