Re: Ball Joint replacement on Foreman 450
I'd avoid sanding out the hole any. The circlip is for "backup" reasons only, and does no more to secure the ball joint in place than the cotter key on the end of the axle does to hold your brake drum on the end of the axle. If the joint is allowed even the smallest relative motion inside the hole, it'll wear out the hole in no time, and it'll leave you somewhere with the tire stuffed up under the rack, the axle pulled out, and wondering how to get it home.
Freezing the ball joint will help to a certain amount, as will warming the knuckle, but even both combined will not (should not) eliminate the "friction fit" of the two components.
You can use a twelve point socket, or a piece of pipe that fits over the ball joint, and will push it by the same outer ring that will "seat" against the knuckle when it's pressed in, and use that to hammer it in, or use that and a vice to press it in. It's awful handy if you have access, but it doesn't require a proper press to get it installed, just patience and sometimes determination.