Selecta is a bottom bracket and crank arm system produced by the Japanese company Shimano. The Selecta brand was manufactured in the 1970s and 1980s, but Shimano dropped the brand because it was unreliable. Like many bottom brackets and crank arms, Selecta has a splined cup that must be removed to disassemble the system. The size of the splines in the Selecta are smaller than other models, but a few standard bike repair tools will suffice when you want to remove the Selecta system.
Mount the bike into the bike stand so the drivetrain side (the side with the gears) faces out. If you don't have a bike stand, turn the bike over and rest it on its handlebars and seat.
Remove the dust cap, if present, from the crank arm bolt (the bolt holding your chain rings, or front gears, and drivetrain side crank arm onto the bike frame). Use the Allen wrench to remove the crank arm bolt and any washers. Set aside the bolt and washers. Remove the non-drive side crank arm in the same manner.
Unscrew the crank puller's centre bolt until the centre mechanism of the crank puller is flush with the end of the tool's inner mechanism. Insert the threaded end of the crank puller into the hole where the crank arm bolt was. Turn the tool until it won't turn any further.
Tighten the crank puller's push bolt with the wrench until the crank arm comes off the bike. Unscrew the tool from the crank arm.
Turn and pull the bottom bracket by hand to remove it. If it doesn't slide out easily, hold one side steady with one wrench while you loosen the bottom bracket with the other wrench. Once loosened, pull the bottom bracket out of the frame.
Removing the Selecta system will require you to apply a lot of pressure with the wrenches, so have a friend hold the bike steady as you work on it. Before installing a new bottom bracket and crank arm, clean the bottom bracket hole of your bike frame with a damp rag. Crank pullers can be purchased from bike shops or online bike tool retailers. It is a tool with a handle attached to a mechanism that fits into your crankarm. When the mechanism is tightened, the bolt of the crank arm loosens and allows you to remove the crankarm.