Bottom Bracket length??

[Revolution]

Quick question - will a UN55 bottom bracket with a length of 118mm be 8mil longer on the drive side than a 110mm bottom bracket or is the extra length shared by both sides?
I'm having to replace a crankset and BB on an old Iron Horse mountain bike. (bearing is shot and crank cannot be separated from the bracket) The Shimano Acera crankset is no longer available. I have found a replacement with the same 170mm crank length and identical 24/34/42t ring size but trying it on a 110mm bottom bracket and the chainline is only 41.5mm on the centre ring (7mm too small) hence my question.

[recordacefromnew]

Quick question - will a UN55 bottom bracket with a length of 118mm be 8mil longer on the drive side than a 110mm bottom bracket or is the extra length shared by both sides?
I'm having to replace a crankset and BB on an old Iron Horse mountain bike. (bearing is shot and crank cannot be separated from the bracket) The Shimano Acera crankset is no longer available. I have found a replacement with the same 170mm crank length and identical 24/34/42t ring size but trying it on a 110mm bottom bracket and the chainline is only 41.5mm on the centre ring (7mm too small) hence my question.

A 118mm UNxx is not 8mm longer than the 110mm. The 122mm (code NL) is.

It is preferable to look up the chainset code (inside face of arm, FC-Mxxx) and identify the correct bb from a Shimano tech doc.

[Revolution]

Thanks - When I ordered the crankset there was no info about the part number but there was a sticker on the inside of the crank arm 'fc-m131'
I followed your advice and searched out a techdoc from the shimano web site which did state that a UN26 was the compatible bottom bracket.
I'm still at a loss as to why the bottom brackets don't have a consistent numbering system but the upshot is that the BB fits and the bike is back on the road.
Thanks again