BB7420 replacement bottom bracket

[Broadside]

The bottom bracket on my wife's Specialized Dolce road bike has developed some play. I have removed it from the frame and it is a square taper marked as FSA 7420 (68 shell) and 116mm spindle.

I can find a replacement RPM branded unit but have read that these are not particularly good quality. I have also found the Shimano UN55 but can only find it with 115mm spindle length. I know it's only 1mm different, do you reckon this will be ok? They also do a 113mm spindle UN55 which is a tiny difference to the 115mm model, which makes me worry that the 1mm could be a big deal...

http://www.chainreactioncycles.com/shimano-un55-square-taper-bottom-bracket/rp-prod71369

 

[Tim Hall]

1mm total difference is 0.5mm per side. How close do the cranks come to the frame on the current one? Now imagine them 0.5mm closer. Is there still buckets of room? If yes, go forit.

 

[PpPete]

IIRC correctly Shimano's "115mm" is actually 115.5mmm , and it would surprise me not at all if FSA's 116mm is just rounded the other way; but even if not, I'm sure it will be just fine, unless you have ludicrously small clearances between chain ring and chain stay.
The UN55 is hard to beat.

 

[Broadside]

Thanks Tim and Pete. The clearances for the cranks and chain rings are not that tight so I will go for the 115mm model.

 

[Broadside]

Just a quick update on this for anyone that is interested; the Shimano UN55 115mm arrived today and it is indeed 1mm shorter than the FSA 116mm unit! The Shimano unit is also 12g lighter which is an unexpected bonus.

I have installed it and there is lots of room between the frame and the inside chainring so all is well. Now that it is installed the subtle but annoying clunky rattle that was on the bike has gone - I had thought for a while it was the rear hub or free hub knocking around a bit but it turns out to have been the bottom bracket all along.