BSA WM20 wheel building

Wheel building .pdf downloads
Building Jig.pdf Front hub parts.pdf Front wheel lacing.pdf
 M20 Frame Dimensions.pdf M20 Front Hub.pdf M20 Rear Hub.pdf
Spoke Sizes.pdf Rear wheel lacing.pdf Truing Jig.pdf

“Very few people attempt re-spoking or truing of wheel rims, considering the task a mystical art quite beyond the amateur. Rebuilding a wheel is surprising simple and requires very little in the way of workshop equipment, so why not have a go? You may not be able to do the job as quickly as a professional but there is no reason why you should not achieve a fair degree of accuracy. The whole operation is well within the capabilities of the novice but requires some thought and a fair degree of patience.”

Radco – Vintage Motorcyclists’ Workshop 

The method described here is not that generally used by professional wheel builders, but suits the occasional wheel builder. I have used it and concur with the above statement by Radco. The money saved by doing it yourself can then be spent on stainless steel spokes and rims. 

The principle is based on using a wheel building jig, also known as a Taverner jig, to do 95% of the work and a truing jig to do the final 5%. Illustrations of both jigs, copied from Vintage Motorcyclists’ Workshop are attached. 

To make the wheel building jig, drill the centre hole first. Use a flat bar as a beam compass and draw about 4 or 5 concentric circles in pencil, starting with a slightly smaller diameter than the rim and increasing in radius by 2mm. When positioning the rim, use a square to center the rim, measuring from these circles. Clamp the rim with G clamps while fitting the rim location blocks. You should be able to get the rim centralised within 1mm. The height of the rim on the jig relative to the hub will depend on the offset. Illustrations of both front and rear hubs, giving the required offset are attached. Note that these offsets are based on a rim width of 76mm. This varies with manufacturer and for a 78mm rim, you will need to reduce the offset by 1mm to retain the same centerline position. 

With the rim and hub in the wheel building jig, assemble the spokes to the lacing patterns illustrated. Take up the slack by hand and then tighten in very small increments, working your way around the rim in a natural rotational sequence. Test the tension by taping with a screw driver. A particularly tight spoke may be backed off and a loose spoke may need an extra turn.  Gradually increase tension to about normal running tension. Test the sound of the screwdriver against an existing wheel to gauge this. 

Remove the wheel from the wheel building jig and transfer to the truing jig for final check and adjustment. You should aim for radial eccentricity within 2mm and lateral run-out within 1mm, by a combination of tightening and slacking spokes, again in very small increments. Remember to grind off sharp ends. 

The above notes should suffice but there is a wealth of further information on the internet. 

Happy wheel building. 

Peter Vlietstra

February 2015