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Dismantling the Upright Norton Gearbox

Writer: Andy Marks
Andy Marks
20 hours ago
3 min read

This guide explains how to dismantle an Upright Norton gearbox and what to look for as you take it apart. The gearbox shown is from a 1947 Norton Model 18, with part numbers taken from the 1948–49 parts books, but the dismantling procedure is broadly similar for the earlier Dolls Head gearboxes used from 1934.

Close-up of a worn metal Norton gearbox assembly on a workbench in a workshop, with bolts and shafts visible under warm light.

For the purposes of this page, let's assume you have already removed the gearbox from the frame and removed the kickstart and gearchange lever.


It is worth mentioning at this point that removing the gears is easiest if the gearbox is in second gear.


Don't forget to drain the oil before you start stripping the gearbox!

Removing the Gearbox Covers and Selector Mechanism

Remove the four Gearbox Outer Cover Fixing Screws (A2/309) and the Cover Stud Nut (A2/307) at the bottom before sliding the Outer Gearbox End Cover (B2/301) off.


Close-up of a spanner tightening a greasy metal Norton Gearbox part with bolts and rust on a workshop bench.

Slacken off the pinch bolt and remove the Clutch Worm Lever (A2/377).

Remove the external gear linkage and Cam Plate Plunger, Bush and Spring (A2/350, A2/351 and A2/352)

Undo the Front Stop Stud Nuts (A2/412F) and remove the positive stop mechanism as a complete assembly. This can be put to one side to be checked later.


After undoing the two Rear Stop Stud Nuts (A2/412R), the Stop Studs (A2/411) can both be unscrewed from the case and the Cam Plate (A2/423) removed.


Use a screwdriver to lever the Kick-starter Return Spring Cover (A2/358) off, then carefully remove the Kick-starter Return Spring (A2/367).


Undo the remaining six Cover Stud Nuts (A2/307) and spring washers (A2/308) before removing the Inner Gearbox End Cover (A2/300).


Removing the Gear Cluster

Unscrew and remove the Striker Fork Shaft (A2/340) using the flats on its outer end.


At this point you should be able to remove the entire gear cluster. Staggeringly, I didn't take any pictures of the gears and shafts laid out on the bench at this stage, so I have no pictures to show you here! The following removal sequence is taken from E. M. Franks, The Motor Cycle Maintenance and Repair Series: Norton (1949).


With the gearbox in second gear, as mentioned earlier:

  1. Remove the Low Gear and Kick-starter Wheel (A2/337)

  2. Remove the Main Axle Pinion (A2/331) - It may need to be levered off

  3. Remove the Second Gear Wheel and its Floating Bush (A2/330 and A2/335)

  4. Remove the Layshaft Second Gear and its Striker Fork (A2/334 and A2/339)

  5. Remove the Mainshaft Third Gear and its Striker Fork (A2/329 and A2/339)

    • The striker forks are interchangeable (hence the same part numbers)

  6. Remove the Layshaft (A2/325) and its remaining gears (A2/332 and (A2/333)

  7. Remove the Mainshaft (A2/324) with Bronze Clutch-Thrust Washer (A2/328)

  8. If you haven't already done so, remove the Gearbox Sprocket (A2/368) - it is held on with a left-hand thread

  9. Remove the Main Gear Wheel (A2/326) from the box

    • This gear contains a set of 13 rollers so be careful not to lose them, or replace them with new when it's time for reassembly.


Wherever possible, I try to keep the gears in order to make reassembly easier.


Next time I am working on one of these gearboxes I will be sure to take pictures and fill the gaps in this article!

Removing the Cam Plate and Bearings

Undo and remove the Indexing Plunger, Spring and Bush (A2/350, A2/352 and A2/351) and Cam Plate Spindle Bolt (A2/348) before sliding both the Cam Plate (A2/341) and Cam Plate Quadrant (A2/343) out of the case.


I would always advise replacing gearbox bearings when the gearbox is apart, especially if you don't know how old they are. They are relatively cheap and it's not a five minute job to get to them if they start rumbling a thousand miles after carefully putting your gearbox back together and into the bike.


Always heat the gearbox case before removing the bearings. With the case sufficiently heated, they should come out without having to force them.


Close-up of a metal ball bearing with black seals on a black background, showing silver and gray rings.

We sell a range of Clutch and Gearbox parts for these gearboxes, including all of the bearings you will need. Click on the image or the link above to see the range.

Gearbox Inspection and Reassembly

Now that you have everything laid out on the bench, it's time for a thorough inspection to establish what can be reused and what needs replacing. Gearbox inspection and reassembly both justify articles in themselves, and I am currently working on these guides. I will link them here once they are published.

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