Most kits come with two size casters. The smaller casters will be installed at the rear of the frame, the larger at the front. This helps distribute the massive weight of an engine.
The casters at the rear are held in place using four bolts and nuts. You'll need to reach into the frame to attach them. Tighten all four by hand, and then use a wrench to tighten them fully. In this kit, the front casters used bolts that screwed directly into the front frame legs. Go ahead and install these, too. Don't forget to use your washers!
