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Help me out please I'm going potty.
Got a 2nd hand Isla Beinn 24". Needs new BB, no biggie. Read conflicting guidance on t'web so remove cranks, measure BB shell and BB length - 68x113, get a shimano BB-UN26 68x113 ordered.
I went to fit the new BB and it has a massively different position or chainline compared to the old one, it's bizzarre. The old BB looks pretty normal - the new BB looks like the drive side is set very far inboard. Taking the calipers to them, there is 15mm from the outside surface of the body to the end of the spindle compared to 21mm on the old BB. The picture below/attached ought to show this pretty clearly.
The new BB was delivered in plastic bag packaging, not the cardboard box I'd normally expect to received shimano BBs in, so assumed this was OEM packaging.
Additionally, the new BB can be fitted up to the plastic NDS sleeve and the resulting assembly is much longer than the 68mm shell!
I didn't think the chainline was a variable given a BB shell dimension and axle dimension? So what don't I know (except for a lot) and what am I missing? New BB was off some ebay rando, so I'm guessing it's a knock-off, or mis-spec?
The obvious answer is that's a 73mm BB that's mislabelled. I can't think of another explanation. Have you measured it?
E-type bottom bracket is designed to work with a BB-mounted front mech which is secured under the fixed cup
Yes - that would push the axle out, 5mm wouldn't it. Might be the "BB-UN26-E" on the shell..
https://bike.shimano.com/en-EU/product/component/shimano/BB-UN26-E.html
Annoyed at myself for having cleared out all my unused BB spacers a few months ago 😣