Let me preface this story with an aside: if you buy a bottom bracket today, you will encounter none of these problems. In fact, if you buy a bike at all today, you will probably never even encounter your bottom bracket at all. It will be trouble free, maintenance free. It will not be a thought that enters your mind.
I, on the other hand, was sent on a lengthy quest, as if summoned by a wizard, destined to toil with hands drenched in grease, hunting for tools, seeking out the help of friends near and far, consulting ancient oracles and runes for guidance. I was dealing with a ball bearing bottom bracket.
Like all enchanted items, this loose ball bearing bottom bracket was of stunning beauty and great renown. I am talking about the BB-M730, the Shimano Deore XT bottom bracket. This one in particular had been resting inside my 1987 Schwinn Cimarron for the past 34 years, like the One Ring in the depths of whatever cave Bilbo goes down into where he gets the One Ring. I don’t know, I haven’t read The Hobbit since I was a kid. I’m getting away from the point!
Here it is disassembled and cleaned with some mineral spirits. Shiny.
OK, on a new bottom bracket, one with cartridge bearings, all you do is tighten down one side of the bottom bracket, then you tighten down the other side of the bottom bracket, and you’re done. You bolt your crankset to it, and you are done. This very vital centerpoint for your bicycle — the bearing system that lets your pedals spin freely — is unbelievably simple. When it finally wears out in a couple years, you buy a new one, and it costs $20.
This BB-M730 works in the same way. There is an axle (a “spindle”) that your cranks attach to, and it is suspended on bearings on either side of the bike. Rather than keep these bearings sealed away in cartridges, the BB-M730 leaves them exposed. You keep them smooth and sealed with fresh grease. As for adjustment, they must be held snug but not too snug. They must not be pressed so tightly that they don’t spin, but they can’t be so loose that they can wobble. If they wobble, they break. If they are too tight, they break. This concludes my explanation of bottom brackets, except that I must note that if you want to go and buy a BB-M730, this titan of excellence, this masterwork of craftsmanship exemplary of Shimano and arguably the entire Japanese manufacturing industry at the time, you will have to PayPal a collector $125 (plus shipping) to get your hands on something in NOS condition. Mine just happened to be what was sitting in my ‘87 Schwinn that I bought for $150 altogether.
What else does a $150 ‘87 Schwinn have? Rust. Mine explained that to me when it snapped in half on a light trail a little over a year ago, and had to get sent to a framebuilder to be brazed back together with molten brass and silver.
Initially, my framebuilder Johnny Coast told me to just strip the back of the frame for the relatively small fix. As he worked on the bike, he realized it was going to be more of an involved effort, and he stripped the frame all the way down so that it would fit on his alignment table and generally be easier to work on. All of my parts went into a box.
A year later, I have the bike back, fresh from getting repainted. I’m putting it together, and doing the bottom bracket for the first time. I do everything right, and there’s play.
If I tighten it down any more, it feels rough, like something inside along the bearings is binding, like something isn’t aligned right.
I realize that in coming back from paint, I haven’t had the bearing surfaces cut smooth. This is called “facing,” and you need to do it to make sure that everything is aligned dead across the bike, not at an angle. I hop on the subway with my bike frame, get it faced, and head home. I reassemble the bottom bracket, this time confident that the problem is fixed and ... there’s still play.
Now, to do this job properly, you really have to tighten down one side of the bottom bracket, the fixed cup, with a 36mm wrench. I don’t have a 36mm wrench; I’ve just been using big old pliers. I wonder if maybe the fixed cone isn’t sitting flush. The problem would be the same as if you were assembling the bottom bracket without having it faced. I call a friend who used to be a bike mechanic, he’s got a 36mm and a lot of experience. I go to his place. We check the fixed cup; it’s tight. We assemble the bottom bracket again, and there’s still play, still rough in spots if we tighten any more.
Somehow this bottom bracket went bad while sitting in a box.
It’s strange because, c’mon, this is a Deore XT bottom bracket. This is the best of the best. The highest of high quality. How could a spindle get bent, or a set of bearings go bad, sitting in a box? It was fine the last time I rode it before it broke.
But then again, Deore XT or no, it’s still a caged-bearing bottom bracket. Who cares? What’s so important about it going bad? This kind of bottom bracket is obsolete and destined to go bad at some point anyway. I resolve to buy a new sealed-bearing unit in the morning. I walk home.
The morning comes and, for some reason, I decide to look up the old BB-M730 on Shimano’s website. You see, Shimano keeps all of its original technical documents preserved online, complete with exploded diagrams, labeled parts numbers, and installation instructions. And what do I see?
Well, in every caged-bearing bottom bracket, you point the cage towards the inside of the bike so that the ball bearings themselves can roll on their cup-shaped bearing surfaces.
That’s exactly how bike tool giant Park Tool instructs you if you watch their instructional how-to video, this is what makes sense. What do I see in Shimano’s original technical document?
The bearing cages face out, not in.
I take it apart again. I re-grease it again. I reassemble it again. Only this time, everything feels right. It adjusts as I would expect. It is smooth as silk, and there’s no play at all.
I will still end up buying a new cartridge-bearing unit just to have in my toolbox as a spare. I will keep it as insurance, because I know that this old bottom bracket will eventually loosen and wear out, and part of me is already over it. But I will also respect this bottom bracket for sending me on this journey, on this quest. I never thought about bottom brackets so much in my life, never thought that I would. It got me, though.