M730 Cranks arms, which BB length?

[mfh126]

I've been looking through my newly acquired Shimano catalogues and found this info coding about M730 BB sizes

70-T-122.5, 68-T-122.5, 73-T-121.5, 68-T-127.5

I assume this means 'Shell width'-T-'Axle length'

So a 68mm shell would require either a 122.5 or a 127.5mm BB axle, that 5mm makes the difference between the 47.5mm chainline and the 50mm chain line

Basically:

68 shell + 122.5mm BB = 47.5mm chainline
68 shell + 127.5mm BB = 50mm chainline

Though I didn't know that you could get a 70mm BB shell :?

Your chailine theory sounds right, but I'm not sure that the 5mm difference between the 127 and 122 spindle is divided evenly between the non-driveside and driveside portions. When looking at a 127 Shimano BB, you'll see that there's a great deal more of the spindle extending on the driveside. Hopefully someone else has more conclusive information for you.

 

[FluffyChicken]

I've been looking through my newly acquired Shimano catalogues and found this info coding about M730 BB sizes

70-T-122.5, 68-T-122.5, 73-T-121.5, 68-T-127.5

I assume this means 'Shell width'-T-'Axle length'

So a 68mm shell would require either a 122.5 or a 127.5mm BB axle, that 5mm makes the difference between the 47.5mm chainline and the 50mm chain line

Basically:

68 shell + 122.5mm BB = 47.5mm chainline
68 shell + 127.5mm BB = 50mm chainline

Though I didn't know that you could get a 70mm BB shell :?

Your chailine theory sounds right, but I'm not sure that the 5mm difference between the 127 and 122 spindle is divided evenly between the non-driveside and driveside portions. When looking at a 127 Shimano BB, you'll see that there's a great deal more of the spindle extending on the driveside. Hopefully someone else has more conclusive information for you.

Now I do know this one (as opposed to the 107/110 length, but I do know that answer to that now*)
Anyways,
For the Shimano Cartridge style, all worth mentioning (CS & UN's) it is in fact divided equally between both sides and the Shell to End length on the drive side for
122.5 is 28mm &
127.5 is 30.5mm

122.5 should be stamped D-NL and 127.5 D-EL


EDIT to add and oddly what I though BUT to the wrong length.
The 121.5 length mus t be a throw back to the older bikes, it's asymmetrical but equivalent to the 127.5 length in chainline (shell to end) though I think in the old cup'n'cones the length increases from 122.5 to 127.5 only change by Shell to end by 1.5mm. But errors on manufacture and tightness of fitting are probably more than the 1mm difference.

Anyway, that's enough for my brain tonight.

 

[Xesh]

I once used a 118.5mm XT BB with my 730s on a bike. Shimano used to make the loose ball BB axles in this size although they were/are extremely hard to find. 122.5mm is the 'proper' size though.