Bottom Bracket Help

[TunaAndBikes]

Still a n00b in Bottom Bracket terms, as i try to set/forget most.
I'm converting an older mtb to my winter bicycle, and need help with choosing a replacement I could potentially service myself.
Right now it has 68mm x 119mm spindle and i'd like to get a cartridge-type for easy in/out replacement whenever I'll need to.
Am i better off with 68x113mm or 68x 122.5 a better replacement?

[oldpotatoe]

Still a n00b in Bottom Bracket terms, as i try to set/forget most.
I'm converting an older mtb to my winter bicycle, and need help with choosing a replacement I could potentially service myself.
Right now it has 68mm x 119mm spindle and i'd like to get a cartridge-type for easy in/out replacement whenever I'll need to.
Am i better off with 68x113mm or 68x 122.5 a better replacement?

Depends on the crankset you wish to use...which one?

[oliver1850]

I have cheap new Shimano 117 and 123 on hand. Shipping to Canada is expensive though.

[TunaAndBikes]

It's an Shimano Exage 400 LX, according to the label.
I'll possibly swap the second ring in for a 46T ring, if that makes a difference

[oldpotatoe]

It's an Shimano Exage 400 LX, according to the label.
I'll possibly swap the second ring in for a 46T ring, if that makes a difference

I'd say a 122.5..113mm the crank might hit the frame..like a shimano UN-55(cartridge bearings)...

[Ken Robb]

are the cranks Octa-Link or square taper?

[dddd]

When replacing a bb or even just the spindle, the overall length may be less important than the positioning of the RH crankarm, since different bb's/spindles often have a different offset dimension to them.
On newer, shorter square bb's, the offset is usually zero, i.e. the crankarms are positioned symmetrically about the frame centerline.

I suspect that the Exage 400LX originally mounted to an offset bottom bracket, while the UN51 aftermarket cartridges are almost all symmetrical.
Note that the OEM cartridge bb's (with their cryptic sizing codes such as "D-NL") usually feature a couple of mm offset, thus positioning the RH crankarm as if it were mounted to a longer bb spindle.

A modern, symmetric aftermarket bb cartridge with an optional ~2mm cup spacer may be the most practical solution, as it allows you some adjustment of the chainline at the time of assembly.

Other than that, I usually prefer to have the very shortest bb spindle that still allows the front derailer to pull in with sufficient authority, and which gives a full mm or two of chainring clearance at the chainstay.