Gear Selector Mechanism

Well having reassembled the gearbox, testing it proved difficult. Its probably easy if you can install it on a bike, but in the absence of a functional LE, testing on the bench involves more than the average number of hands! You need to hold the box tightly whilst turning the output shaft (clockwise when viewed from the rear) and moving the selector shaft to try and select the gears- When you are turning the shaft directly the direction is clockwise to change up and anticlock to change down. The box functions as one-up-three-down when turning the selector shaft directly; the pedal rod mechanism will reverse this action when fitted to the bike. The trouble is all of this is quite stiff in action and having to hold the box as well means that three or 4 hands are really required.
In my case the gears would change but seemed to only allow me to select 1st and second plus neutral. After trying very hard to convince myself that this was right I decided to bite the bullet and strip the selector pawl mechanism to check that all was really OK.

Removing the box lid again revealed the selection mechanism, note edge notched selector camplate and pin driving slots in the plate itself

The central shaft is bolted on the exterior so I held that nut in a vice and unscrewed the central shaft starting with an offset screwdriver

Shaft then pulled out freeing the camplate...

Which could be removed to reveal the pawl mechanisms beneath, Note the spacer which lies beneath the plate (centre) and fits over the central shaft to raise the camplate to the correct height. The sprung and hooked "striking pawl" is on the left and the domed and sprung "indexing plunger" that engages with the grooves on the edge of the camplate is still in place in its wired housing upper left. The camplate has been inverted to show the ratchet plate into whose recesses the sprung striking pawl will hook. It is essential that this ratchet plate is not detached from the camplate rear, or if it is, it must be put back  on the same side of the camplate, the same way up and in the same orientation, the lug on the ratchet plate pointing towards the hole in the camplate as shown. In my case the discs apeared to be a unit and didn't come apart anyway. I found the whole mechanism a bit rusty which might make it too rough to rotate easily  so I cleaned all the surfaces and smoothed them with emery cloth.

The striking pawl spring had seemed weak earlier and this could be the reason- on gentle prodding it fell into two pieces! I ordered a 30mm x 5mm compression spring to replace it although this is slightly too wide (original 4.7mm- I hope the surplus 0.3mm will not prove a problem.

Domed indexing plunger had seemed seemed to be stuck in its housing and I suspect this is grooved internally, so I will smooth that out with a tight fitting drill bit rotated by hand in the socket to make sure it can move freely. Spring seemed to be in good condition and the head is still  nicely rounded. The free length of this spring should be about 0.75 inches so I'll check it and replace if necessary.

I reassembled everything and refitted the lid to the box taking care to engage the forks in the gearchange camplate. To be honest the change mechanism wasn't greatly improved although it did seem to be better- probably because of the spring replacement. The main problem remains the difficulty of bench testing the box although it you do need to turn both shafts as two gears are selected on each. If fitted then engine rotation would be doing this anyway but on the bench its pretty awkward. However I was able to engage and disengage all 4 gears! So success in my book anyway.

I have been called away by urgent Lotus requirements so I don't know when I will get back to the Velocette, but I will write more when I get around to this bike which sadly currently languishes in storage.