68mm bb in a 73mm shell

So I swapped a bb and crank between two bikes and everything seems to be working perfectly but afterwards I realised the new bike (a diamondback) has a 73mm shell.
My question is- does it matter?
Kes

P.s. Its a un71 bb

no. As its working then all must be fine. could be issues if you change cranks? How is the chain line looking?

The chainline is perfect despite it being a 68mm bb

Thanks
Kes

your driveside crank will be 2.5mm further out than it would otherwise be

It should knock the chainline in a bit, but then of course crank and what it was set at before would be needed ( if same setup then it'll be out by 2.5mm to before, so at a 50mm chainline and not the previous 47.5)

Only other thing is over time it may start to wobble as the NDS will not be clamped down fully* and the crank will be inwards 2.5mm to before.
Which might not be a problem (if say a 110 was used and not a 107)


* Though with a UN72 the clamping cup should be able to go in under the shell.

Thanks for your replies
Yeah I meant un72 not un71!
Anyway everything seems solid and the shifting is perfect front and rear so fingers crossed it'll be OK
Kes

Just be careful that the main part of the BB isnt floating. The end of the cartridge body will be 4 - 5mm away from its cup.

Not necessarily, probably not at all.
I assume the OP is using a shimano sq taper sealed unit. The fixed side (right hand) screws all the way to it's stop (the BB shell) and will be like it should regardless of what width it was designed for.
The left side will need to screw well inside the BB shell and so the LH crank will be nearer the LH chainstay.

My Rockhopper has run like this for about 10 years no problem

Essentially what this post says is that theres no difference between a 68 and 73 mm shell Shimano bb....

The fixed cups (which control the whole position of the bb) on them are slightly different to cater for the extra metal on the shell. It's just you.dont notice because it isn't a huge difference

if that's what you read, then sorry, my bad explanation. There is certainly a difference.


yeah, I think that explains what I wrote badly.

I think the driving factor on whether the OP is ok, is whether he can screw the adjustable cup far enough into the BB shell to hold the left side and stop it rocking. It is likely the whole cup will be immersed into the shell, so needs to have threads cut deep into the shell.