Bottom bracket help!!!! KONA related!

[mayco]

I needed a new bottom bracket for my 93 Explosif.
The old one is a UN72, 68mm cup, but the axle measured 124mm.
I can only seem to find either 122mm or 127mm.
I fitted a 122mm but the tiny difference puts too much stress on my chain resulting in it snapping twice. Has anyone experienced this and knows of a solution.
The new bracket is really heavy too! a light replacement would be preferable.
Many thanks

PS it's running with a Sugino Mighty Crank if that helps.

 

[one-eyed_jim]

There's no plausible reason why a 1.5mm change in bottom bracket length (0.75mm per side if the difference is symmetrical) would cause your chain to break. Perhaps your chain was on its last legs already.

Shimano never made a 124mm UN72 as far as I'm aware. What are you using to measure?

You don't say what make or model your new bottom bracket is, but light replacements in longer axle lengths are relatively thin on the ground. You might pick up something from eBay or the classifieds here. Avoid titanium axles though, unless you're a lightweight yourself.

 

[Andy R]

I needed a new bottom bracket for my 93 Explosif.
The old one is a UN72, 68mm cup, but the axle measured 124mm.
I can only seem to find either 122mm or 127mm.
I fitted a 122mm but the tiny difference puts too much stress on my chain resulting in it snapping twice. Has anyone experienced this and knows of a solution.

As far as I know there was never a 124mm UN72 - sure it's not 122.5mm?

Anyway, 1mm difference in chainline isn't going to cause a chain to snap - did you adjust the front mech. to suit?

The best that you're likely to find (at a reasonble price) isthis. Available in 122.5mm.
Ok, it's not the lightest but it's not like you're going to notice the difference once it's fitted

 

[mayco]

oh dear!

Hmmm, i used vernier calipers, i may take another look!
I have bound to have read them wrong.
I measured them in a blind panic after breaking the head off the crank bolt, 1 hour before the shops shut,
the night before a 7am start on the London to Brighton bike ride. A stressful moment i can tell you!!!
I bet they are 127mm

edit: yes they are 127mm, could this be the reason for a chain snap?