Mechanics and Fixing Any Questions Answered

Had one in front of me. Pried it off a bit and you can see it butts up against the machined section on the spindle, it's made of steel and too far away from the bearings to be of any use as a seal or dust cover. They're there to stop you installing the crank too far on, you may not need it if you reach installation torque before they contact but if you don't it'll stop them going on too far. Most BBs don't have them and I've always thought they're a bit weird.

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If you want to be able to see the gear you are in you can use the Alfine or XT/XTR Di2 one

I have one of these I'll realistically never use.
It is not compatible with certain batteries though so may not work with the external one

Always thought it was (combined with those ears that stick out of the inside of chainset) to stop the chain jamming in the gap between BB spindle and inner ring.
You can pull them off if its causing problems, just a press fit.

Edit, talking of shimano UN300, had a weird one of the other day, screw threads on the drive side stopped about 5 full threads before the collar with a solid chunk of alloy (full height of the thread inside of the valley height), ended up taking a burr grinder to it. BB axle clamped in vice, then just let it spin like a kind of master bodge lathe setup. BB has plenty of threads on it, and they usually aren't threaded all the way upto the collar. Was a 122/123 x 73mm, never seen that before.

Hmm ok Yes, its a weird component on a bb

Majority of bbs I have serviced have the plastic ring instead of metal and it travels right to the bearing. The cheaper bbs have them but its not the best seal, you still end up with grit etc.

I suppose the plastic ones are used for a tighter seal to "try" keep the weather out and the metal ones could be used for the crank arm installation.
It wouldn't be ideal for a plastic ring to be pressed against a machined edge with a crank arm tightened on. The ring would fail or your crank arm would get loose.

I have not seen one before that stops at the machined section but I know for sure, that little ring does not keep the spindle in place. The bearings contacting the spindle inside the shell keep it in place.

but yes weird haha

It is not compatible with certain batteries though so may not work with the external one

Good point, have a look at this too corny: https://bike.shimano.com/content/dam/e-tube/assets/images/contents/project/compatibillity/pdf/en/HM-CC.3.4.3-00-EN.pdf

I had one of those too on a 1x11 setup and then had Alfine Di2, being able to see what gear you are in is very useful for Alfine.

Shimano tiagra 4700 are adjustable between caliper/ canti and v brake.

I know for sure, that little ring does not keep the spindle in place.

Yeah, never meant that, meant as a stop for the cranks. I've seen plenty of shitty seals come off like you mentioned and it's not one of those, the picture way back didn't look like one either.
Could also be to stop the chain getting stuck but the one I had up there is a 113mm and I don't think there would be room for that anyway.

oh okay, yes, a v weird component.
Ill keep an eye out for some steel ringed bbs, i wanna check one out for sure.

imagine the complicated convo about all the weird spacers and seals on external bbs hahaha

That's a UN300 113mm.

https://dassets.shimano.com/content/dam/global/cg1SHICCycling/final/ev/ev/EV-BB-UN300-4708.pdf

it isnt listed on the blown up pdf document. (its not the chain case stay)

but it reads "Better chainline stability with chain line stabilizer" Maybe this is what they are for. Chainline stability???? (Photo attached)

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chain line stabilizer

Yeah, almost like a stop for the crank.

Hey took me a while but I finally got around to trying one of these and it worked perfectly, thanks for the suggestion! Moving the guide over did stop the cable rubbing on the chainstay but because of the position the cable was cutting inside which reduced the tyre clearance, which is now sorted with the high rise guide.

Yeah thats I think what they mean, they just needed some marketing blurb to make it sound more important. Likely because lower tier/no name chainsets have random tapers, so can get wound onto the taper too far = issues.

Yeah, I was just being a bit sassy and pointing out it's what I said it was ages ago.

Glad I could help. Those guides are very useful to help with clearance issues.
The also keep the shifting cable at a constant distance to the downtube which just looks neat.

Can a stop on a taper work though?

Wouldn’t it sort of defeat the point of the taper?

That's exactly what I thought when I first saw them and why I think they're s bit weird, I guess they're in a place where the taper is engaged enough and it just stops things going a mm or so too far. I think I've fitted cranks that reach torque specs before hitting it so it's more of a backup than anything else. Square taper is a bit shit anyway.

I've never had a problem with square taper, and like the ability to vary spindle length, but seen plenty of disasters with cranks being wound on too far by people beasting the crank bolts and butchering the tapers.

Is this anything to be alarmed by? There is a very thin impression running up the carbon steerer of some forks that I have just purchased along with a very lightly used second hand frame.

Is it just from the machining process? It is very uniform - I have seen steerers that have been marked from compression before from a stem being over-tightened and this doesn’t look like this but you never know right… @gbj_tester

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Bit of a topic dredge but…

@snottyotter @Netakure

Am struggling to remove dub cranks from a frame, have tried handlebar over Allen key, impact driver, and setting torque wrench to 100 but cannot get the bolt to shift. Any suggestion? Am guessing choosing the hottest day of the year wasn’t a great idea… but my garage is relatively cool.

@brommers can I borrow your difficult crank tool- could you make me one?

Solved.

Used some steps to support the nds crank to stop the cranks rotating. Then leaning over the bike could push down on the drive side crank with left hand and used an extended Allen key with right arm. This meant the cranks were being stopped from rotating at two points and my weight was also resisting their spinning while also undoing the stubborn bolt.

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Nicely done, I've done a few with the opposite pedal being held in place by a big old work bench.

Looks like a mould split line

Cheers. I thought as much. I actually found some compressed carbon elsewhere on the frame and am going to return it, so it’s all somewhat academic now