Shims on the drive gear serve two purposes, to prevent the bearing from rubbing on the gear and to take up any tolerance developed when the teeth are cut into the bear casting. Tolerance is calculated based on the number of cuts a tool has made since installed in the machine and factory QC. After the fact we it’s trial and error which shims to use, and where. That’s why you got four. The smaller copper shim is typically installed on the back side of the drive gear between it and the side plate. The three other shims are installed on either side, usually only one on the toothed side and one or none on the back side. Note the different thicknesses of the three remaining shims. Start with the thinner shim on the toothed side of the gear and just the copper-colored shim on the back side of the gear. Add or remove thickness using the other shims if the gears feel a bit rough or the if the handle becomes too stiff.