Handy Tricks Seven! Things to do to and with bicycles!
To see even more handy tricks, check out the rest of the saga at Handy Tricks 9: Oodles of random tricks
and Handy Tricks 8: Island Handy Tricks
and Fifty Handy Tricks.
and 40 More Handy Tricks
and Australian Handy Tricks
and Guatemalan Handy Tricks
and Yet More Handy Tricks
and Handy Tricks Six!
For a bunch of things that didn't work, check out How Not To
First trick: Improvised Freewheel Removal Wrench
Every brand of freewheel has a different pattern of grooves inside it. If you don't have the right wrench you usually can't take it apart. Unless you can improvise one. This method works well for the most common shimano freewheels.
Remove the axle from the wheel.
Insert the biggest hex wrench you can find into the freewheel. Pound some nails or a big staple as seen here into the grooves to lock the wrench in place. Unscrew the freewheel. Wiggle the nails out.
To learn about why you'd use this tool, what the real one looks like, and everything else about bicycle mechanics, look at Sheldon Brown's site
and Park Tool.