Re:
It enjoy the fun of getting things to work and learning about what I have, it keeps it interesting.
I was meaning the bottom bracket from the donar bike, white rust coloured thing.
That should have the correct length in assuming it was all original.
It'll be 113 for the Impel cranks.
Normally you aim for the middle ring (as its a triple ring crank) to sit at 47.5 to 50mm from the centreline of the bike (middle of the dowmtube, bottom bracket shell etc.
Always aiming for the lower chainlone if possible, but being square taper it's never perfect.
Bolt that crank down as though it was fitted, then measure from the middle of the bottom bracket shell ( or outer edge as it's easier, but adjust half of its width 68/2 to the chainline)
Since you have no ring measure to its flat face mountpoint to get an idea. On that crank you can see a slight ledge and if you measure to that it'll be about right.
Take that measurement and then you need to remove that much from the drive side. You could assume it was easy but shimano bottom brackets come in steps of diveside length changes, so normally 107/110 113/115. 118/122 etc will give the same chainline
So assuming the 113 gives a 47.5mm (call it 4
chainline, you might find on the 127 it is sat at ~55mm.
(21 or 89mm from the edge of the bottom bracket frame shell,)
It inact as the lenght of bottom brackets can be .5 and are rounded due to tradition and weather you measure to the centre of the teeth or the inside of the ring at the teeth (some companies did)
Easy explanation
http://www.sheldonbrown.com/chainline.html
