Bicycle Mechanics - Replacement BB question

does anyone know what size BB would work as a replacement BB for a late '90s Hardrock. i have heard 68 x 113 mm. i was wondering if maybe a 115 or 118 mm would work or if those lengths would mess up the chain line. i figured it'd be better to ask and get the right thing instead of spending money on the wrong bracket. i'm building up an old Hardrock into a SS and i tried a 68 x 107 mm and it was way too small. it wouldn't allow chainring or crankarm clearance. any thoughts or options would be appreciated..

thanks

It depends on the crankset.

I need a new BB for my 1997 Trek 830 Mountain Trail. I pulled the BB on it now, and there were no numbers on it. How do I determine the size I need? I assume I measure the diameter and length of the tube that holds the bracket. Is this assumption correct?

Thanks.

One number is the length of the shell in your frame that the bottom bracket threads into, and the other number is the length from one end of the bottom bracket spindle to the other end. At least that's how it is for the square-taper BB's in mine. e.g. I have 68x113, where the BB fits into the 68mm BB tube in the frame, and its spindle is 113mm long from end-to-end.

Thanks. that makes sense. I also have a square taper. So I get this straight.. If you were to put a 68x118 (if it even exists) into your bike, the BB would still fit into the shell, but the crank arms would be further apart because the spindle is 118mm instead of 113mm, right?

I think I understand.. I can now rip my bike apart again and go shopping for a new BB.

thanks.

That's what I found out through reverse-engineering when I took mine apart. Measure 'em and shop. I'm not sure if all square taper sealed cartridge BB's are alike, though I'm not sure how different they could be.

does anyone know what size BB would work as a replacement BB for a late '90s Hardrock. i have heard 68 x 113 mm. i was wondering if maybe a 115 or 118 mm would work or if those lengths would mess up the chain line. i figured it'd be better to ask and get the right thing instead of spending money on the wrong bracket. i'm building up an old Hardrock into a SS and i tried a 68 x 107 mm and it was way too small. it wouldn't allow chainring or crankarm clearance. any thoughts or options would be appreciated..

thanks


the crankset is an old Sugino triple ring crankset that i got for cheap off of ebay. i'm only using the middle ring and i think it'll work with a longer spindle length. i just wanted to know if a spindle length longer than 113 mm would screw up the chainline in a SS application.