Transmission Shimming

  > I find it interesting that I have three different instructions now on shimming, and they are all a little different.

     Here's a fourth or maybe I should say another third method. If one of the shimming methods you are speaking of is the one from Moto International, I would throw that one out. Richardson recommends installing all the gearbox shaft in the transmission end plate, putting the end plate in a vice and adding or subtracting shims until you can shift through the gears smoothly. While it is comforting to actually see all of this taking place it is unlikely that this method would result in a smooth shifting box. With the shafts unsupported on one end, they splay away from each other by quite a bit. If you cup your hands around the unsupported ends and pull them together, so that they are all parallel as they will be when installed in the box, you can watch the sliding muffs climb up the lay shaft as the shift fork shaft, shift drum shaft and lay shaft are brought into better alignment. It is these sliding muffs that you are trying to precisely locate via shimming.

     There is a much better method that I use for determining correct shimming of the gearbox. Shim the drum for clearance as described on the Guzzi tech page and then assemble the complete box. Remove the large gear oil fill plug. Through the fill opening you can see the sliding muff for first and second, the engaging dogs on first and the engaging dogs on second. What you want to see is that when in neutral, as you rotate the end of the lay shaft, there is an equal clearance between the dogs on the muff and the dogs on the gears as they pass each other. Then engage each gear {1st and 2nd} noting the depth of engagement of each. A careful visual assessment is all that is called for here. At this point any inequality in the depth of engagement is corrected by shift drum shimming. Remember to maintain the same "total" shim thickness as determined when you clearanced the drum. So when you remove .2mm from one end of the drum, be sure to add .2mm to the other. While you cannot see what is going on with the 3rd, 4th or 5th gears, there is no separate adjustment for this anyway. The location of the shift fork for 3rd and 4th is predetermined by the distance between the tracks in the drum, so when 1st and 2nd are perfect, the remaining gears should be as well.

     Why did I say the remaining gears "should be" perfect? Because I had a drum in a gearbox once that was machined with an incorrect distance between the 1st-2nd and 3rd-4th shift fork tracks that was IMPOSSIBLE to set up to engage both pairs correctly. Wow!
charles cole