The Top Gear Nut (Old Model) is a critical internal component for the gearbox of vintage Royal Enfield motorcycles, specifically those equipped with the traditional 4-speed right-shift cast-iron engine. This nut is used to secure the top gear (sleeve gear) onto the gearbox main shaft. Key Features Precision Engineering: Designed to withstand the high torque and rotational forces of the gearbox’s final drive assembly. Material: Typically manufactured from hardened alloy steel or durable brass to ensure long-lasting reliability and prevent thread stripping. Finish: Often comes in a polished chrome or natural brass finish, providing both corrosion resistance and an improved aesthetic for the gearbox casing. Authentic Fit: Specifically sized for old-model 350cc and 500cc cast-iron engines, ensuring a perfect match with the original threaded shafts. Critical Safety Component: Restoring or replacing a worn nut is vital to prevent main shaft play, which can lead to oil leaks or significant gear transmission failure. Technical Specifications Feature Details Compatibility Bullet 350/500, Standard, Machismo, Electra (Old 4-Speed Models) Reference Part No. #550131/A or similar depending on the specific nut kit Material Options Alloy Steel, Brass, or Stainless Steel Function Secures the sleeve gear/main shaft within the gearbox casing
