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I'm trying to work out what my frame is, and what size bottom bracket it needs (68/71/73 mm), and the recommended spindle length. I've attempted to measure both and it seems to have a 68/115 bottom bracket.

I can't find any serial number on the frame, but someone told me, circa 2002 that it looked like a Marin.

Complete bike

Complete bike

Yoke

Yoke

Rear

Rear

Rear wheel hub, note the unusual markings

Rear wheel

Rear from top

Rear from top

Crank

Crank

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    Do you really need to know what the frame is, or just the BB spec? Shell with is very easy to measure, threads are almost certainly BSA/English. Can you measure the spindle length of the current BB cartridge? – Argenti Apparatus Apr 30 at 20:54
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    The lockrings on the outside show it’s not a cartridge type. Both cartridge and loose bearing type fit in the English thread shell though – Argenti Apparatus Apr 30 at 21:47
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    Take it to a bike shop. They'll be able to identify the bottom bracket by looking at the one you have. – David Richerby Apr 30 at 23:21
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    100% go for a cartridge BB unit - they are far superior to cup and cone. Also, its a nice bike, worth maintaining and caring-for. Might look for some Magura horseshoes to help reinforce the brake posts would be my only suggestion. -- they're an optional part. – Criggie May 1 at 1:02
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    Tough crowd around here, pictures of bike from loads of different angles, and yet still somehow attracted a down vote. +1 from me at least for being one of the best written 'ID my bike' type questions i've seen – Andy P May 1 at 15:09
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You probably will waste more time trying to identify the bike compared to just replacing the BB.

Two options - Easy but likely more expensive - take the to a bike shop have them supply a BB of the correct size, if they supply the wrong size, they should be prepared to swap it.

Or buy one cheap off the internet (probably 68x115) and if its the wrong size, well you have a spare the wrong size for you current bike.

Its unlikely a spindle length of a couple of millimeters too short or long (i.e. one size up or down) will make a major difference. The worst happens is the front derailleur rubs when cross chaining. BB are cheap - $10 for a cheapy, $20 will get a reasonable quality one for that bike. So it won't break the bank if you buy the wrong size first time.

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