A loose mainshaft bearing has allowed the sprocket, sleeve gear and bearing to move slightly inwards resulting in the chain gouging a groove into the back of the gearbox. I dry assembled the box with the inner case and mainshaft with gears and found that when the bearing is loose the sleeve gear can slide in 1.5 mm. before it come up against the shoulder on the spline. Is this normal or is there anyway of reducing this potential movement with shims? Obviously its not an issue if the bearing remains tight in the housing, but if it becomes loose again during service I'll have the same problem.