Brian Johnston original idea posted on Delphi Vulcan Forum
If you've done even a single oil change on your bike you may have noticed (on Vulcan's anyway) there is no magnet on the drain plug to catch little shards of ferrous metals before they can do serious damage. Ok, you're right, there aren't supposed to be bits of metal floating around in the crankcase but if anything is breaking down or you're just breaking in a new engine then there will be some bits and pieces.
You could spend big bucks buying little magnetic pills that you drop into the oil filter or you could fork over cash to buy curved magnets designed to surround your filter. But why when you probably have a perfectly good and very powerful magnet stashed in a desk drawer or cardboard box full of cast off computer parts? No? Then ask your I.T. department at work. They'll have a box of old drives someplace.
Inside every hard drive is at least one (sometimes two) very powerful magnet (s). Since you'll want to destroy a broken down drive anyway to make sure nobody can ever retrieve your personal information you may as well make it a useful experience.
Just open the top of the drive, unscrew the nut holding the swivel arms in the drive and remove the arm (you might have to do a little twisting but what the heck, you're destroying the thing anyway right?
Depending on the manufacturer the magnet might be held in place with a dab of glue or just through its own sheer force. Use a screwdriver to pry the magnet off it's mounting surface. With just a little 'persuasion' the magnet will come off. Now scratch and bend the drive disks up a little to make them completely useless (some people take a torch to them) and toss the drive.
Now just attach the magnet to the outside of your oil filter. Voila ! Instant trap for any little bits the filter might have missed.
You might want to use one of these magnets on the outside of your drain bolt too. What the heck, you were going to throw the drive away anyway right? With any luck the force will be with you and the magnet will help change traffic signals too.