Dolls Head Gearbox

Hi David,

   These gearboxes have external linkage which is prone to wear from road dirt. The clevis pins and their holes wear to an extent that the cam-plate is not moved fully. The quick fix for this is to fit new 1/4" clevis pins and re-set the rod adjustment. Fit the top pin and pull the gear lever up to first gear position and the check the bottom gearbox arm is properly engaged in first gear, then adjust the rod so the bottom pin goes in easily. If the holes are badly worn, you might find it then jumps out of top. To overcome this you could use 9/32" or 7mm clevis pins and enlarge the holes.

   You can get an idea of the general gearbox condition by removing the outer primary chaincase and checking how much end-float there is, if the clutch moves more than 1mm the box will probably need a rebuild. These are fairly straight-forward to rebuild if you feel able, or have a look in the OBM etc.

Just to confirm what Richard has said..Even when the box is in good condition, the adjustment of the links is crucial. Taking out all the slack in one direction will mean that the other adjustment suffers.

They're wonderfully simple boxes with very little of the shimming nonsense that lesser makes required into  the 1950s but the mainshaft bronze thrust washer has quite a lot of work to do. I'ts an easy fix though.

I find it a good idea to adjust the linkage in one of the intermediate gears...2nd or 3rd...and then let the end gears 1 and 4 sort themselves out.  I think the WD manual says this.

I once spent a while on the lathe making close tolerance snug fit pins. They didn't work.  The upper and lower levers are at right angles, so they need enough slack to rock a little in the 'wrong' direction.

One lesson is to keep the oil level well up. Low oil not only risks damage, but it affects the gear change.

... about absolute authenticity then a pair of Rose joints would eliminate much of the free play. Probably not available with Cycle threads but 5mm internal threads could be opened up and retapped as there's generally enough meat there.