I agree, add the fourth wheel while your in there. If the skid is out, it's a cake job. If you want to leave it in, well it gets a little more interesting. I made a bullet point that threads on to the end on the axle so that when your trying to push the axle back through it self aligns all the spacers and washers, I was even suprised at how well it worked. It looks liek Yamaha is now selling the tool in their accessories, I would recomend it as it can save a lot of frustration. Also don't replace the outside wheels with the same ones, get ones that you can change out the bearings on.