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Facing Bottom Bracket Shells on the Catrike

Yesterday I did a bottom bracket shell facing and thread cleaning job on Bob Shaver’s Speed. I took lots of pics of the job showing the steps in getting clean faces on each end of the shell.

After reading the text below each pic, it’s very interesting to watch them all in slideshow mode. The progress shows up much better that way.

shell-before-facing-with-labels

This is the bottom bracket face before it was faced, showing the layer of powdercoat. The external bearing cups press down on this face, and if it is not perfectly flat the bearings are cocked to one side.

facing-tool

This is the Park tool for facing the bottom bracket faces.

tool-facing-the-bb

This is the cutting tool cutting away the powdercoat layer, and a tiny bit of metal.

cut-but-not-finished

This is the face showing slight chatter marks from the tool.

finishing-facing

The chatter marks are smoothed off and the face made perfect with emery cloth pressed in by the cutting tool.

finished-bb

The face after the final smoothing and polishing.

This facing of the bottom bracket edge is part of Bob’s upgrade to ceramic bearings in the BB. They are typically much tighter than the steel bearings that come in most bottom brackets, so they will not tolerate as much misalignment as the steel bearings. This is why the faces of the shell must be absolutely parallel with each other and perpendicular to the axis of the bottom bracket spindle when converting to ceramic bearings. The Park Tools threading and facing tool is a very precise piece of equipment that does a beautiful job of truing up a BB shell, even if it is very expensive. Most shops will do this job for about $50 if they have the tool, but most mechanics, in fact very few, know how to do the job correctly. They usually leave the chatter marks. That’s OK, actually, as long as they are even all the way around the face.

As can be seen in some of the pics in Bruce’s flicker photos (linked below), a lot of powder coating gets deposited on the surfaces where the bearing cups tighten. This uneven buildup causes the cups and bearings to cock sideways, as the powder coat is never perfectly smooth. Cheaper and sloppier steel bearings will absorb a lot of this alignment displacement, but better ceramic bearings won’t, and it will often cause bind in the better, tighter bearings. Pictures iL1, L2 and L3 in Bruce’s flicker pics show the non-drive side of the BB shell with a huge buildup of powdercoating. This is enough to cause bind in even a steel bearing. If you look really close at these pics, you can also see the only three small areas of contact that the bearing cup had with this face!

Besides the powder coating buildup, warpage from welding will distort the shell faces. This is shown in the pics as small areas at a time of bare aluminum showing up as cutting progresses. If they had been absolutely true from the start, the aluminum would have shown up all at once as soon as the powdercoating was removed.

If any Catrike riders intend to put ceramics in your BB, or you feel some resistance and just want to feel sure about your’s, and your lbs can’t do this job. Contact Bruce and if you ask nicely he may do it for you. You will need to send him your bare boom/BB and return postage. (Oh, and a pan of brownies!)(Hey! it never hurts to ask!) Contact Bruce at rbb@antelecom.net

This is the link to Bruce’s pics on flickr

Bruce

P.S.  mikeatlbch made a comment that jogged Bruce’s memory, and he is right.  mikeatlbch notes that facing the bb is needed only for external bearings, not for cartridge bearing assemblies.  Thus the Speed, Expedition, and 700 model Catrikes, which all have external bearing assemblies,  need to be faced.  Other Catrike models or any bike/trike with cartridge bearings don’t need to be faced.

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