BB UN-51 won't fit?

[FluffyChicken]

Yes, so the pic wasn't your BB.
It should still fit in if you're fitting it properly and doing drive side first.

 

[Martini-night]

Nope,still doesn't fit. I've done everything by the book drive side first etc etc. Gonna file dow 3mm of bb drive side end threads tomorrow morning

 

[d8mok]

Where are you based? If you local to Chesterfield I’ve drawers full of different BB’s you can try

 

[Martini-night]

Newcastle mate, my pal is coming in the morning with a couple of files to file down the end BB thread. Wish us luck!!!

 

[doctor-bond]

Something is stopping it from going all the way in
The cup hitting the spacer thing in the middle?(something bent or not compatible)
The edge of the bb shell not ‘faced’ (build up of paint, etc) 2 mm? Hmmm.
The BB threads being blocked at some point - chase them out.
The bb shell width incompatible (68 vs 73) already discounted.

If you file or cut some of the threads away, it might work - but what is the problem you’re fixing? BBs don’t usually need such attention. I’d need to know the reason.

 

[benjabbi]

The first thing I'd do in this case is chase the BB shell threads but then I have easy access to the bloody expensive tool for doing so. The trouble with filing the thread on the actual BB is that if the start of the thread ends up less than perfect you run the risk of making a complete mess of the thread in the frame. I'd take it to a shop and have it faced and chased.

 

[bikeworkshop]

^^Frame Threads need chasing, that's all.

 

[FluffyChicken]

The first thing I'd do in this case is chase the BB shell threads but then I have easy access to the bloody expensive tool for doing so. The trouble with filing the thread on the actual BB is that if the start of the thread ends up less than perfect you run the risk of making a complete mess of the thread in the frame. I'd take it to a shop and have it faced and chased.

That's why I recommend the old metal bb cup, a cheap DIY chaser
But not quite as good as the real thing.