It works like this: The cups are pressed into the frame neck,
so it becomes all one piece. The bearings are pressed onto the stem,
and freely ride around in the races in the cups. This means the only
thing connecting the front end of the bike to the frame are these 2
bearings. Everything around the outer circumferance of the bearing
is fixed to the frame (shown in red). Everything else is anchored
around the stem (shown in green), and freely turns (along with the
handlebars, forks, and front wheel)
Look for cups that have the races already pressed in; it'll
save you a headache, plus the complete package is cheaper than buying
the individual bits. I bought mine off the wall at Hi-Way.
Step 1: The cups need to be pressed into the frame neck.
The cups are a noticeably larger diameter than the inside of the neck, so some
mechanical force is required. The smart way is to set up a couple plates
on a bolt and tighten it down to push the cups in. We didn't think of
that, so we just wailed on the things with some planks of wood. We're talking
a hundred full overhand Captain Kirk smashes with a long 2x6. It took a
while, but we got them home eventually. Remember to grease the metal first.
Step 2: Prepare the lower tree. Slide on the larger dust cover, and seat
the lower bearing on the stem. The bearing is slightly smaller than the
collar on the stem, so again it's a press fit. Instead of whaling on the
poor bearing with a pipe or something, Sean borrowed an oxy-acetylene torch.
Just heat up the inner race until it gets blue (but try to stop before it's
red) and then it'll just slip on, no force required.
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