If you get your left side case all assembled (bearings pressed) and you find there's a little too much end play...... you can surface grind a small amount off your center spacer. Some look like this (others are completely round with "timken" stamped on them). If it's too tight (you need a thicker spacer, because the bearings are smashed against the races). That's why the instructions are so strict on using the supplied spacer with your bearing kit, since all the tolerances are set up for that particular combination of bearings and races. When you install your pulley (or compensating sprocket) it could take up a slight amount of end-play, so you need to take that into consideration too. It's pure luck any of these garage builds work as good as they do with so much shit that could happen to just ruin your day ! Hey, why's my motor making these squealing sounds ???????