Rebuild | Triumph unit twin: Measuring up

As progress continues, it’s apparent there are different ways to measure things and some misplaced components make a reappearance.

Words: Tim Britton Photographs: Tim Britton and Fiona Watson

There are readers out there, I’m sure, who do know how many different combinations of BSA fork, wheel and brake plate parts there are.

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However, I’m not one of them and thankfully for this feature I don’t need to know the finer details. Having solved the lack of front wheel spindle last issue – I bought one from Burton Bike Bits – and fitted the front wheel I’ve been using in my 650cc Triumph when it’s in scrambles mode, into the project, to see if I could get any idea on the sort of off-set the new wheel is likely to need, several things became obvious.

First, the wheel sits tight against the timing side fork leg – I expected it to be close as the Triumph yokes are different to the BSA ones, but not as close as it is.

This alloy tank was going to be put to one side and the steel tank refitted for the moment, then an idea for mounting it occurred.

The brake plate I have for the project is similar to the one from a WDB40 used on the 650 wheel, but not the same.

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Another difference is the locating stop for the project plate; the fork legs are obviously different as there is no lug for it to sit in, so, thinking that I’d get away with it, I cut a piece of aluminium sheet to fit the old plate – no chance.

Rocker boxes will have to come off so the pushrods can be fitted.

There was little option left but set to and fit the new plate and hub in place and start again.

At the same time, I tweaked the spindle so the UNF thread was removed and still left enough spindle to cut a new 9/16in Cycle left-hand thread and clamp everything up in the wheel department.

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This type of arrangement is an option for the rear mudguard, however after writing the piece a glance at an internet auction site showed someone selling some alloy rear mudguards, pre-owned apparently, or second-hand.A bid is in… Ooh, the excitement!

I might have to be creative with the other end as the Tommy bar hole may be inside the spindle clamp, but that’s a minor thing.

The shoulder of the thick part on the spindle needed moving back a little and this is within my lathe use capabilities.

Read more and view more images in the August 2019 issue of TCM – on sale now!

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