FORKS STRIP/CHECK & RAISE GEARING

1

I had fitted ordinary two-hole fork tubes, unaware that double-damped tubes have four larger holes (top). Changing them didn’t sort the damping, so time to look closer... 2

Domed nut secures the damper rod (as standard these ’68-type forks had a solid top nut with an internal thread so the rod was screwed in from beneath). 3

Cycle thread lock nut screwed tight-end onto a long bicycle stem bolt made a tool, to fish down the hole for the rod as it sinks out of reach or check damper effect. 4

After slackening bottom yoke clamp bolt, taper fit of fork tube in top yoke will need to be freed with a downward tap on the slackened top nut (or a BSA fork tool). 5

There’s a BSA tool for unscrewing the chromed fork seal holder; this one has pegs to engage in slots inside to avoid risk of leaving grip marks on plated surface. 6

Some of these forks have a cup washer to retain the bushes, but mine has older-style circlips; they can be tough to prise out – don’t score the fork tube surface. 7

Remove the damper-retaining Allen bolt screwed up from the fork bottom. The extended oil drain screw locates to prevent the damper turning with the bolt, so make sure the screw is in place. 8

Damper may come with the tube or get left behind. Remove the bottom bush nut (there are two types – extended one gives more compression damping). 9

Slide bushes off fork tube followed by fork seal holder. Fork tube thickens nearer top, so to prevent stretching the seal its best to fit/remove it from the bottom.

10

On the damper rod there’s a spire clip and a rubber washer. The washer is intended to prevent oil getting up and out of the top nut, the clip keeps it from sliding down the rod. 11

Two circlips hold the damper assembly together. Careful; wire one keeps top bush in place and is easily dislodged if it catches on reassembly. 13

The bushes were a bit slack, so I turned oversize ones and machined the oil flutes using a dividing head and ball-nosed cutter on the milling machine. 12

Inside is a top bush, an upwardfacing cup that rests on a starcollar, then a grooved bronze bush and finally a locknut. Not much wrong here... 14

Back in the lathe, fitted to the rods for final turning to the best possible fit – there’s less play but I’m not sure it’ll make any difference. 15

Nope, they still top out despite trying thinner 15w oil in case it wasn’t moving around fast enough and then heavy SAE 40 to slow things down. 16

Gearing’s easy to raise: Norton clutch is one tooth smaller than a BSA – equivalent to half a tooth on the crank sprocket (the one you change). 17

A cam on free spinning sprocket is spring-loaded against another, splined to crank; engine shocks are dispersed by cams compressing spring. 18

I accommodated extra sprocket tooth in chain adjustment – reconnecting the chain is made easy using this old ‘Sa-vu’ chain pull tool.