Adjusting for fly and drive pin wear in Yale hand change locks can be a challenge. This wear can also cause difficulty with a comb change on the 101-1/2. When new, the wheel spline teeth should align properly, allowing the outer wheel to easily re-engage the inner wheel. Difficulty in getting the change key to return to vertical is a good indication the teeth on one or more wheels are misaligned. Before tearing into the lock to see what the problem is, experiment with positioning the wheels slightly off the index mark, starting with the 3 rd number. Identifying this type of problem is virtually impossible with the lock disassembled. Once the key turns back to to vertical, find the centers of the wheel gates through dialing diagnostics and live with the fact one or more numbers of the comb may work best at half numbers.