ET: Engine (Twin) Twin gearchange

[jim burgess]

I have been carrying out adjustments on a twin gearchange. On the bench the change was fine, as per the riders handbook, on the road it would pop out of 2nd when changing up from 1st and pop out of 3rd when changing up from 2nd. It did not do this all the time of course, oh no! This is a Vincent and nothing can be predicted. So I have had the cover off and been through the process all over again and observed the following... the gaps between G43 and G59AS were not the same above and below, but when I adjusted for equality I actually ended up with no gaps at all, just complete contact.
When I set to adjusting the G57, I experimented with the extremes of adjustment to note the effects and then set about finding the compromise in the middle. I have no idea what the practical outcome of these adjustments are yet until I have another trail on the road, we shall see.
My questions are...

Can someone explain to me how the heck this mechanism works, what is the theory behind this mechanical marvel?
Why is it like this, was this just an expedient way to avoid someone else's patent?

I have been through this process before with the Norvin, there I had to hold the lever down whilst on the road to retain the box in 3rd gear, and minor adjustments cured this issue.

I know there have been a couple of threads on this subject before, but any comments and tips to help understanding would be gratefully received.
Cheers
jim

 

[greg brillus]

The adjustment of the G57/G49 are critical to the actual full selection of the gears........one way too far and the box will either over select or in reverse under select the gears again either shifting up or down.......this then causes the box to jump to a false neutral.........The adjustment of the G61 is merely indexing the G59 AS assembly verses the G43 ratchet so that each time the shift lever is back to its neutral position, it can locate correctly the next tooth on the G43 to shift up or down the next gear. When setting up the shift adjustment, place the G66 AS lever on its pin, this without the G 40 shaft and the G 59AS pawl assembly in place........using a spanner hold the G66 AS lever in its full up travel, using a texter pen put a mark on the alloy plate behind in line with this full travel, then do the same with the lever fully down........Remove the G66 lever and reinstall the other shifting parts followed by the G66 lever.......Now go through the gears rotating the back wheel to allow the gears to change easily.......as you rotate the G 66 lever down from gear to gear check on full lever travel that the marks you put on the alloy G50 plate previously align closely to these full travel marks........repeat the process coming back down the gears and see if the same applies with the upper texter mark.........If you temporarily install the gear indicator lever on the end of the G40 shaft you can feel if each gear is clicking fully into place via the indexing plunger within the gearbox.......If the adjustment is out you will quickly work out if the G49 needs to be turned clockwise or anti clockwise to allow the gears to fully select........This adjustment is the main and primary adjustment of the box.......the ratchet adjustment via the G61 plate is secondary........There are many aspects to the gear selection quality........very often the E80 nuts on the battery tray are not pushing firmly against the inboard side of the G50 pate.......once the footrest hanger stud is fully tightened, this will readily bend in the top of the G 50 plate......this causes the shift to become lazy and sometimes the shift lever becomes stiff especially as the engine heats up.......the problem gets worse as the cases grow and the steel shafts do not.......On some high mileage machines.......the shift ratchet parts wear and selection starts to suffer.......the best and easiest way is to simply replace these parts and the quality of the shift will be returned to normal........this is especially the case with the G 43 ratchet itself....the internal teeth on the G 59 AS pawl assembly are very hard and do no wear as much I've found........All in a days work really........Cheers.......G.