Shimano square taper BB question

[oliver1850]

Looking at a bike on eBay that has a 105 square taper crank and I see that the cup is labelled BC 1.37 73. Does the 73 mean the frame has a 73 mm shell or does it indicate something else? BB appears to be a cartridge type, the 73 is stamped at the edge of the drive side cup.

[gbcoupe]

I think that would be for a mountain bike? Not 100%. No dirt or gravel around here without a drive.

[Brian Smith]

No, it means that the bottom bracket was intended to give the "right" chainline for the drive system when installed new in a 73mm shell.
2.5mm difference in the chainline may be very little depending on application, or it could make the "wrong" bb give just the "right" chainline, depending on application.
If this is a road frame, chances are it's a 68mm BB shell. If it's the "wrong" bb for your usage, a 2.5mm spacer under the photographed BB lip would put it all right.

[oliver1850]

It seems that you are saying that the BB was meant to be used in a 73 mm shell. Would the left cup end up sticking out beyond the shell if it was installed in a 68 mm shell? Not sure if I have a pic of the ND side.

[oliver1850]

Does appear that the left cup sticks out more than it should, so it must be a 68 shell.

[Ken Robb]

What size BB do you need? I have a longish one I bought to use on a triple.

[dddd]

Does appear that the left cup sticks out more than it should, so it must be a 68 shell.

Looks like someone added the superfluous lockring to hide the protruding cup.

I wouldn't space the right cup out at all on this bike. If the chainrings clear the stays and the front derailer pulls the down to the small chainring with authority, the chainline dimension is very likely not too small.

But the left crankarm is very likely further outward than it needs to be, though I consider this secondary in importance to a good minimalist chainline dimension.

If the offset arm bothers you, or if the chainline is currently any bigger than it needs to be, then I would use a 68mm bb having a considerably (at least 5mm) shorter spindle.

[boywander]

OP- depends on the chainline and clearance, this can be easily remedy with 2.5mm spacer on the fixcup side centering the 73mm bb in a 68mm bb shell.

[oldpotatoe]

Does appear that the left cup sticks out more than it should, so it must be a 68 shell.

HA..seen this more than once..a cartridge BB, meant for a 73mm shell, stuck into a 68mm shell, with a worthless lock ring on the non drive side..

Depending on the BB, the OP can probably tap the RH cup off, get a proper set of 68mm cups and bob's yer uncle. Or, as has been mentioned, a spacer on the RH side to get chainline and crank stance correct.