I am fixing up an old schwinn continental from the early 70s and was wondering whether it was possible to put cartridge bearings in the bottom bracket
Can you clarify if you mean a cup and cone housing, to change from loose bearings to bearings in a metal retaining cage? Like this:
ANSWER 1 These can totally be used instead of loose bearings. There are fewer balls to carry the weight, and over time the cage may break down and get chewed up.
OR do you mean cartridge bearings with ABEC ratings like this:
ANSWER 2 No, these can't be used without major re-working of the bottom bracket. There are adapters to do this, but they won't be cheap.
OR do you mean a cartridge bottom bracket like this:
ANSWER 3 Yes this works perfectly, is dead simple, and relatively cheap. Plus they're greased for life and never need adjusting. When they get crunchy, replace. I've done this on all my bikes.
Not directly. A sealed cartridge bearing needs a machined surface to mate to and your old bottom bracket has threads in the way.
Furthermore, with an 80s Schwinn you might have problems finding the right threaded cartridge bottom bracket. You can, however, use a universal converter like the Velo Orange universal bottom bracket:
It has sealed cartridge bearings and the universal (threadless) design means it'll fit in most English/French/Swiss bottom brackets.
Phil Wood also used to sell a similar type of product but I'm not sure if they are still in production.