Been scratching my head over this one now for about 3 nights, so hopefully someone can help.

Just swapped all the kit off one frame (old BFe) to another (new Pig X), and have got rid of the BFe. Running Shimano XT 760 crank with a Race Face single ring and an MRP MiniG2 chainguide. Now, as both frames are 73mm bb shell I was (naively) thinking that everything would just swap straight over (but now know that the BFe is a 48mm chainline, the Pig is a 50mm chainline).

So, for starters, I set up the BB as standard, one 2.5mm spacer on DS. Small washers spacing the chainguide by about 1.5mm. With this configuration, the ‘clocking’ of the chain was really nasty, with the chain really crossed-over in the lowest gear. So, I swapped the spacer over to NDS, but then the inside of the cranks caught the chainguide. Removed the washers, so the cranks turn.

If I am running the same gear from one frame to the other, and swapping the BB spacer over to NDS, then surely that should keep things the same?

I’ve checked the chainline front and rear, and the front is sitting at around c47.5mm, whereas back is c44.2mm (Hope ProII with Shimano 9sp cassette). I’ve done a rough check on the frame alignment, and it looks pretty much ok.

Basically, I need the chainring to be slightly further inboard, but having already swapped a spacer to the other side, that is not possible.

Any ideas?

So, I swapped the spacer over to NDS, but then the inside of the cranks caught the chainguide. Removed the washers, so the cranks turn.

Just spotted that this is wrong – although I’ve tried so many different combos over the last few nights, that my poor brain is addled.

The pic doesn’t really show much of the issue, but I guess what I was trying to show was that even setting the BB up wrongly, with cranks that should be closer to the centreline too, the chainline is still out, and back pedalling sees the chain drop off the lowest cog straight away.

So, someone must have an idea? Frame alignment, ISCG tabs alignment or position, BB shell out of alignment relative to frame? 😕