Poster just has an obsession with BB bearing preload on items that to most, are install and forget, until they need replacement.

Interesting, sincere thank you. If my external bearings are same, that means preload is (also) loading the sides (inboard on outer race, outboard on inner race) of the bearing grooves. I need to ponder what that means in terms of spreading the bearing load better. On hub cup and cone bearings (angular contact), preload has made a huge difference to me in durability. If the external bearings are different, perhaps not. But they do come with a torque spec on the cap, and after the first retorque, no loosening for almost 2 years and counting. Whereas with internal cartridges, they just keep getting looser and looser after that starts.

EDIT: Can't yet find online, if any externals use angular contact. But did find this snippet: Internal may be stronger as bearings are fully supported by the BB shell, whereas with externals being cantilevered outside the BB shell, with the bearing carrier being aluminum and thin section thickness at the corner to the threads, taking a big huck (jump) may be more likely to fracture that carrier on externals.

EDIT: Some makers, such as Wheels Mfg, offer a choice of "standard" ABEC 3 BB bearings for BSA 24mm, or "angular contact" at higher cost.

My externals are brand-x same as my crank, so not a clue what bearing type.

Good question and comments asking about the difference on an online discussion board, but won't allow me posting the link, or even the name of the board. Discussion is titled:

Are the angular contact bearings worth the extra cost (Wheels Mfg BB)?

You don't need to ponder anything. Standard bearings are not designed for side loading to remove play.

And you have completely misunderstood the cap torque. They list .7 to 1.5 Nm, but then provide a tool that you use by hand and is designed to slip from your grip when it is sufficiently tight. That is supposed to work out to .7 to 1.5, but functionally it is just enough to locate the crank are against the forces of shaft and thread friction. The cap is there to remove play, not preload anything.


You are one of those people who has convinced yourself that your narrow experience and engineering textbook knowledge cause you to have a better, smarter understanding of how bikes work. But bikes don't work like jet engines. They exist in a low torque, low rpm, low temperature world where virtually all the wear and tear comes from bad specs and dirt - not treating the bearings in some super special way.

If you were having problems with bearings wearing out quickly, it was almost certainly due to something you were doing wrong, or out of spec BB shells. So I wish you would stop inventing stuff and then telling people about your new wisdom. You don't even know how the equipment you already own works.

I wish, for the life of me, I could find where online, years ago, they had a superb explanation on bearing life versus proper preload. It was great, and has proven to be true for me. It makes sense, and explains why I was spalling cones and balls years ago when I would adjust the cones for just the tiniest bit of slack, based on dad's advice on bearings, "better a little too loose, than a little too tight". He used to snug tapered roller bearings on front car axle, then back off "two flats", so 120 degrees. I later learned this is way, way wrong, it results in bad roller edge loading, and he was an automotive engineer, but didn't have as much knowledge with regard to rolling contact bearings. Bicycle bearing loads are not huge, but the difference between loading almost half the balls per side and only a couple, makes a huge difference in wear, **especially during peak loading, like 10 events per life cycle, like severe pothole load**. Bearing loads matter for lifespan. This is something I have experienced. Perhaps a high preload is not needed, just taking out the slack, but either way, it's much better than leaving in the slack, which, by the way, also stretches the seals radially. I torque my cap to specs, just like you said in metric equivalent, I could have guestimated it, but I have a microtorque wrench which makes it easy. The crank maker did include a plastic wrench, but if they only wanted people to use that, they wouldn't have made the interface a standard Allen socket, nor labeled it with torque value.

The biggest difference in durability has been with pedals; Cup and cone with tiny balls, proper preload has made a huge difference in durability, versus intentionally leaving in the tiniest perception of slack.

Just because knowlege comes from outside bicycle mechanics, doesn't mean it's wrong. I appreciate you noting that Shimano externals are not angular contact. But evidently some externals are (in my revision above while you were posting). And taking out slack on straight radial bearings may help, I have to think about that, my guess is, with just a small preload, it still behaves mostly like a pure radial bearing, but the preload to one side, taking out the slack, makes it perform better.

I'll be curious about the wheel hub setup on my new bike, which is supposed to have cartridge bearings front and rear, so I wonder if the spindle just clamps axially to the inner races of each bearing, or if there is any side preload between inner and outer races across the two bearings?

Bicycle bearings don't get preloaded. Period. They don't have enough load to make it worthwhile to start that way, so that thing you can't find does not apply.

If you want to learn about current bike parts, read their manuals. No: no lateral preload.

I would be fascinated to learn what the exact recommended "preload" might and how one goes about measuring it. I hope that it's not the old BS about compressing a 10mm steel tube linearly with a quick release.

Since everyone with a QR bike and a set of cone wrenches knows that the hub does indeed change bearing adjustment with the QRs closed, which BS are you referring to?

On Park Tool's website, they have a long and detailed article about cup and cone bearing adjustment. For this discussion, this is what matters:

The above indicates just taking out any slack, no tighter. This would definitely apply to road racers, where drag is everything.

For me, durability is everything. When I left the tiniest slack in my bearings, they wore, they spalled. Perhaps just adjusting out any slack would have prevented that. However, looking online for more knowledge, I ran across an article from a bearing manufacturer regarding proper preload, and I went with that as follows: To sense preload, you need to be able to spin the axle in your fingers, not wheel around fixed axle installed. There are various ways to replace the folk dropouts with spacers to check preload with QR closed. If, spinning axle in your fingers, it feels "notchy" (what Park Tool calls "binding"), the preload is too high. Even with no slack in the bearing, if it feels the same as that, in my experience, too loose, no preload. In between those two, is a setting where it doesn't feel notchy, but you can feel all the balls engaged when spinning; That's the sweet spot. On my current bike, getting this was extremely easy because I don't have QR axles. No axle spacers needed. The way it feels adjusted off the bike, is identical once installed. Adjusting to that sweet spot, on hub bearings, pedal bearings, BB spindles (cup and cone, not cartridge), drastically improved durability and eliminated need for readjustment, going on years and 10K+ miles now. Again, perhaps I would have had same result by only adjusting out all slack, but no axial preload. Don't know. I'll let you know if I find out.

EDIT!:
https://www.gmnbt.com/resources/guid...aring-preload/

Cone and cup bearings are angular contact.

QED.

Regarding the source of this discussion, external BB bearings, I don't know if mine are angular or radial contact.

More info (other website, and this time I'm bookmarking them all): "Excessive preload reduces durability. Lack of preload can cause "ball skidding". (I found evidence of ball skidding, linear spalls, in past rebuilds where I had small slack in hub and pedal bearings, no preload.)

Hey, I never got around to updating this thread. I managed to bank out that tube from the frame, and I did install the Shimano BSA Krankboks, 68mm (122.5mm version) I bought. As I feared, it was too wide, but I just accepted that, thinking that it was only a matter of aesthetics.
Then I left the bike alone because I also needed to change the freehub -- it took a long time to arrive and I had to focus on other things.

Now I finally got around to putting everything together and it rides great, but! I noticed that when I roll the bike back (only when I roll it back, the freehub is installed properly), the pedals turn back by themselves. When I do that having the chain on the biggest cog of the cassette, it goes out to the next cog by itself. If I lift up the back wheel and pedal backwards, it's the same story: when on the biggest cog, it goes out to the next cog out.

Eventually, I figured out what was happening. It's related to my new bottom bracket being too wide, as I initially suspected.

https://cimg1.ibsrv.net/gimg/bikefor...7cd33975ac.jpg
Bottom bracket too wide.

What's happening is that the overwide bottom bracket is causing the chainring to be too far out in the direction shown by the arrows in the picture below. This is resulting in a misalignment between the chainring and the cassette. It's hard to see it in the picture, but the chain is not centered in the chainring.
https://cimg8.ibsrv.net/gimg/bikefor...5e6ce13671.jpg
Chainring too far out

Ultimately, the result is the chainring pulling the chain out when I pedal backwards, as shown mid-action in the picture below.
https://cimg3.ibsrv.net/gimg/bikefor...2478596072.jpg
Chain being pulled out from the big cog

I think it's all better illustrated in this final image:
https://cimg5.ibsrv.net/gimg/bikefor...cf69fde779.png
I had originally thought that the derailleur needed adjustment, so I went through the process today until I discovered the real issue. Due to the nature of this misalignment, the pedal thankfully doesn't move when I'm rolling the bike forward or when I'm coasting. Most importantly, the chain doesn't automatically hop to the next cog under any circumstances while riding the bike. It's all as smooth as can be.

So now my question: Is it worth changing the bottom bracket again? Could this misalignment be causing any damage or be dangerous in any way?

chainline/
 

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Yes, the chainline is off. Pedaling forward, the rear derailleur bottom pulley compensates and straightens the chainline before the chain reaches the top (jockey) pulley. Pedaling backwards, there is no rear derailleur between the chainring and cogs, so it can't do that for you. On MY bike, I had spaced the crank 4mm out because I had an interference issue at the front derailleur cage due to a very fat seat tube (folding bike), and it was constantly dropping the chain when shifting onto the inner ring when on the low (largest) cog. I fixed the interference issue and removed the spacers so the chainrings and chainline was correct as the bicycle gods intended, no more dropping chains. If you are not suffering similar problems, you could leave things be. But you can also correct the chainline if you desire. Note: I would NOT try to space the cassette out at all; I wanted to do that because my chain would sometimes jam hard between the small cog and dropout, so I wanted to make that gap smaller, and put a spacer behind the cassette, however that greatly reduced the engagement of the threaded lockring, and small cog on the freehub shoulders, enough that I did not feel things were sound, so removed the spacer. And changing the rear derailleur from the inferior Dahon compact design to a normal RD and mounting location, cured the chain dropping off the small cog.

P.S. - My 2X chainset specifies 43.5mm as chainline, bike centerline to middle of 2X rings, which matches the middle of my 7 speed cassette on 130mm rear hub. The crank is a hollowtech 2 style so no separate bottom bracket spindle. And spacing the crank out 4mm also reduced the left arm clamp area that much and it came loose. Design specs are design specs.