Sean Flores wrote:
>
> I'm looking for some tips or a quick tutorial on how to correctly
> press sealed bearings onto bottom brackets like the Omas Big
> sliding and Stronglight Ti (which I think may be the same).
The bearings are a very light press fit, both in the cups and on the spindle. They usually have a bit more friction going into the cups than onto the spindle, probably just due to the larger surface area of contact.
In my experience when you remove a cup from the frame, the bearing comes with it (stays in the cup), but if not, it won't be hard to remove the bearing from the axle. Just tap on it, say by laying an open-ended wrench (big enough to clear the flange on the axle) against the inner face of the bearing, and tap on the wrench with a hammer, while holding the axle's outer face against something immovable (anvil, vise etc).
Extracting the bearing from the cup, if it stays with the cup, is a bit harder and may require some skill with a drift punch. Hitting with a punch on one side then the other tends to want to cock the bearing at an angle to the cup -- though it can't really move at an angle, the force wanting to cock the bearing has a tendency to wedge it in, making movement in the desired direction a bit tricky. The best tool would hit the bearing on both sides at once evenly, to eliminate the cocking force, and I have made such tools, sort of like the Campy "rocketship" punch for removing headset cups from the head tube. But the OMAS/Stronglight bearings I have worked on came out easily enough and did not need a special tool. Email me for more details if this is not clear or it doesn't come out easily.
Once the old bearings are off, you might be able to push the bearings onto the axle and into the cups by hand, or with a small amount of persuasion. Once you get them started enough that the cups can thread into the frame, you can use the cups threading into the frame to push the bearings home. You'll feel light resistance as you thread the cup in, until the bearing is all the way into the cup and up against the flange on the axle, at which point high resistance will be met and the cup won't thread in any further. At this point, back off on the cup a bit to reduce the preload on the bearing, and lock as normal with the lockring on the BB cup.
If you have cups with lockrings on both sides (as opposed to the traditional fixed cup on the left), then you have the option of adjusting the chainline a bit, but otherwise the procedure is the same.
Mark Bulgier
Seattle, WA USA