If its not a really nice bike, and if you have a hollow seat post, just squirt oil down the seat post until the oil runs out the bottom bracket, ride for a few days and repeat until the oil runs clear. Then, a little oil a couple of times a year and never worry about taking it apart.
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Il faut de l'audace, encore de l'audace, toujours de l'audace
1980 3Rensho-- 1975 Raleigh Sprite 3spd
1990s Raleigh M20 MTB--2007 Windsor Hour (track)
1988 Ducati 750 F1