BB shell width?, at danger of being confused by the obvious! Options

[Jarl]

Ok, so, I have a bike, which has a BB in it, which says on it "68" (among other things, but nowhere does it say 73). So, I took that to mean the BB shell was 68mm wide... duh...

However, I just measured my BB shell with a tape measure from one end to the other. It's 73mm. This is confusing!!


So will the BB that says "68" on it (shimano UN53) fit an actual 68mm BB shell frame? Or is it a 73mm BB with a confusing sticker?

[1gearnoidea]

go by the shell width m8..so 73 x whatever your larger number is 113/117 etc...must be a dodgy sticker

[coyoteugly]

go by the shell width m8..so 73 x whatever your larger number is 113/117 etc...must be a dodgy sticker

A 68mm will fit in a 73, but the axle will be longer on the drive side. Take note of how close each crank arm is to the chainstay. I had this out with a LBS on the phone the other week. he was saying it didnt matter they would all fit each other etc. Glad i dont trust my bike to anyone but myself, when it comes to repairs.

[Jarl]

Ahh, that kind of clears the muddy water. Yet another thing my LBS screwed up . Now I think about it though, in a way it's good that they gave me a 68mm BB, else I wouldn't have anything suitable for my new frame (getting it very soon!!! like, 2 weeks!! )


I'm guessing a 73 won't fit a 68?

[JohnC]

Ahh, that kind of clears the muddy water. Yet another thing my LBS screwed up . Now I think about it though, in a way it's good that they gave me a 68mm BB, else I wouldn't have anything suitable for my new frame (getting it very soon!!! like, 2 weeks!! )
I'm guessing a 73 won't fit a 68?

You want a 68 for a 68 and 73 for a 73... but some manufacturers supply only a 73 BB with spacers to make up the difference (2.5mm either side).

[Jarl]

Ok, dropped into the bike shop who decided to fit my old bike (73) with a 68 BB. Asked him about it, and apparently if you put a 68 in a 73 you can rip the threads out (it was a struggle to not mention that this is exactly what he'd done to my bike, but I was in a good mood) as the sleeve on the other side doesn't provide enough support, so the BB can move (bad!).

And as JohnC mentioned, a 73 in a 68 is ok, but you need spacers either side.

[LonesomeCowboyBe...]

Ok, dropped into the bike shop who decided to fit my old bike (73) with a 68 BB. Asked him about it, and apparently if you put a 68 in a 73 you can rip the threads out (it was a struggle to not mention that this is exactly what he'd done to my bike, but I was in a good mood) as the sleeve on the other side doesn't provide enough support, so the BB can move (bad!).

And as JohnC mentioned, a 73 in a 68 is ok, but you need spacers either side.

Blimey Jarl, Take it somewhere else or do it yourself

[Jarl]

Myself, thanks! That place is fairly appalling. Not a chance they're ever getting my bike again! Probably better off with halfords

[JohnC]

Myself, thanks! That place is fairly appalling. Not a chance they're ever getting my bike again! Probably better off with halfords

Just buy the tool and do it yourself, it's not rocket science. The tool will probably cost about the same as labour for the bike shop to do it and you'll be better equiped for the future.