Hi guys, just a quick question. I would like to know what this kind of small ring is. When I install my crankset, it stops against it. When I tighten the crank bolt and then remove it, I don’t need a crank puller—the crankset comes off by itself. Does this cause any problem? Thank you.
by hero_peipei
7 Comments
Yes. Your crank should stop at that spacer and be tight. Sounds like your crank arm is bored out.
This sounds wrong. I think you might have a ISO crank and this is a JIS Bottom bracket.
Many people don’t know this but there is two types of square taper BB. Iso is what ie campagnolo used to build..
Nowadays only JIS is commonly used. But if you have a old crank it might me iso..
As for the purpose of the ring I don’t know but my guess is to prevent DMG to the crank from over tightening.
That ring is what shimano calls a chain line stabilizer. It stops the crank arm from bottoming out in the JIS taper.
The ring is a spacer so you can install a chain case or chain guard holder like this one
[https://www.hebie.de/en/protection/chainguard-accessories/chainguard/970/](https://www.hebie.de/en/protection/chainguard-accessories/chainguard/970/)
BB-UN300 = Standard
BB-UN300-E = E-type
BB-UN300-K = chain case
Can you show us the crank arm not installed? Specifically, a nice crisp photo of the square hole taken from the inner side of the crank?
It appears to be a “limiter” to provide exactly the correct chainline with some newer cranks. This is the most coherent answer I could find: [https://www.bikegremlin.net/threads/square-taper-bb-limit-spacer.423/#post-1800](https://www.bikegremlin.net/threads/square-taper-bb-limit-spacer.423/#post-1800)
If your older crank clearly bottoms out on the spacer, I would pull that spacer out like instructed in the link above.
In your comment you mentioned having a “silstar” crankset, which I presume to be Sakae Silstar. As a Japanese crankset it certainly uses a JIS axle and should be compatible.
Your finger