064639 – Norton Commando 850 MK3 Gearbox 2nd Gear Mainshaft (from Engine #306591)

Norton Commando 850 MK3 Gearbox 2nd Gear Mainshaft – Part Number 064639

Norton Commando 850 gearbox 2nd gear mainshaft (Part# 064639) — correct replacement for the MK3 850 gearbox from engine number 306591 onwards.

This is the correct second gear mainshaft (part number 064639) for the Norton Commando 850 MK3 gearbox, introduced from engine number 306591. Part 064639 is the updated 2nd gear mainshaft that replaced the earlier 040418 gear and must always be fitted as a matched pair with the corresponding layshaft 2nd gear 064640. Do not mix these later gears with the earlier pair (040418 / 040019) – they are not interchangeable.

This gear was introduced on the late 850 Commando MK3 to address durability issues with the earlier 2nd gear under hard use. The updated gear features improved tooth geometry and is identified by the AHB marking. When replacing 2nd gear on any Commando from engine number 306591 onward, both gears (064639 and 064640) must be replaced together as a set to avoid mismatched wear and gear noise.

This part is for the Norton AMC gearbox as fitted to all Commando models from 1968 onward. Recommended for any gearbox rebuild where 2nd gear wear or jumping out of 2nd is diagnosed.

Part Number: 064639 (mainshaft 2nd gear)
Paired with: 064640 (layshaft 2nd gear) – must be replaced as a pair
Fits: Norton Commando 850 MK3 from engine number 306591
Supersedes: 040418
UK-sourced, genuine specification

Fair Spares New England – UK-made Norton Commando parts shipped from Massachusetts.