Enfield hub bearings

Your late vintage Norton will be fitted with Enfield hubs. At the rear there will be a bolt-on brake drum and a vane type cush drive for the rear sprocket. Enfield front hubs, with rather ineffective braking ability, were also fitted. Typically, these hubs contain "bicycle type" cup and cone bearings (see the two pics on top). Correctly adjusted and well lubricated they will last a very long time but as few people bother to lubricate their wheel bearings you will most likely find them worn beyond further use.

The first option is to try and locate a new set of cups and cones though this may not be easy as no one I know of stocks them. A faster way out may be to fit more modern alternatives.

Enfield hubs employed by some other manufacturers in the late twenties and thirties were fitted with two unsealed single row ball races MJ5/8 (R and M designation). Alternative designations for the same bearing are MS7 (Hoffman) or RMS5 (Skefco). The outside diameter of their races is 1.8125” (1 13/16” or 46.038 mm). These bearings are still available and may be obtained from your local supplier.

With use of modern bearing adhesives you can fit a pair of these MJ5/8 bearings to your Norton's hubs, after first turning up a suitable spindle and spacer. The hub as used by Norton in most cases is of a larger outside diameter than the MJ5/8 at 1.815” to 1.818” (46.101 to 46.177 mm) and therefore a drop of Loctite is required to fit them properly. Alternatively, sealed metric bearings of type 6204 can be used of which the 47mm outside diameter is ground down to 46.101 to 46.177 mm.

During the thirties another solution was available in that both Timken and SKF produced taper roller bearings of which the outside diameter of the outer race was also 1 13/16” and the inner race was conveniently threaded 9/16” x 20 TPI, the same as that of the regular wheel spindles used by Norton. These taper roller races can be used as direct replacements for the original cups and cones. That is, if you can find them and if you are willing to pay, as they will be expensive. Incidentially, the rear wheel of my M18 is fitted with a Japanese version of the same bearings (bottom pics), the reference can be seen in lower pic. The reference numbers of the older taper rollers appear to have been:
Outer, 1.8125” x 0.565” 1129X (Timken) or 2K-1129X (SKF). Inner, threaded 9/16” x 20, with flats for adjustment: F1175XL (Timken) or 1201799 (SKF). Inner, threaded 9/16” x 20, for fixed position on spindle: F1174XL (Timken).

(All info provided by Simon; thanks!)