This is a simple swing arm and idler wheel arrangement, fig. 6. None of the dimensions is critical, except for those which place the idler in line with the timing belt. The swing arm (part 39) is a block of steel, milled to the required dimensions. It is bolted to the frame with relatively hefty 8mm cap screw as it needs to be solidly fixed to the frame in use. The axle (part 38) is a simple turning and tapping job and is fitted to the swing arm with Loctite, photo 16. The idler wheel (part 39) was turned from a steel offcut. Its reamed bore runs directly on the axle. A steel to steel bearing would not normally be ideal, but in this case, the rotational speeds are so slow that it is of no consequence, although the axle should be oiled of course. The wheel is retained on the axle with an M5 cap screw and washer, photo 17.
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