Gear set #4 in the illustration is actually two gears pressed together with the hydraulic press. The larger one is the stock gear, and the smaller is the new gear. But the large Kymco gear doesn't always match the small new gear so you have to find a standard Chinese qmb gear to replace the Kymco gear. You may be lucky and everything fits, or you may not be so lucky and then have to search out a qmb replacement. You won't know until you take it apart and press the gear set apart. I suspect Kymco purposely makes it difficult so that owners don't mess with the innards.