I'm converting my bike with a rear hub kit, and whilst I'm at it I want to replace the bottom bracket, as the bearings have some play in them.

 

Took it out tonight, and its 68mm housing with a 116mm spindle. I am going for a Shimano BB-UN55, which comes as 68 x 115, or 68 x 118. Would it be best to go for the shorter or longer spindle? Would it even make any difference?

 

Thanks.

you'll need a minimum 122mm spindle, best 125mm or 127mm to host a left side pedal sensor.

The left crank is always prone to loosening because of the torsion through the spindle, so it needs to be really tightened, also a 1mm gap is desirable between the inner face of the crank and the pedal sensor casing.

 

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

 

http://wooshbikes.co.uk/2018/hubkits/left-pas2.jpg

Look at the gaps between the cranks and the BB shell to see how much room is there for the pedal sensor. If there's not enough room and you don't want to modify the sensor, you'll have to get a longer one, otherwise, you can get one close to your original length. if you get one too long, the front derailleur (if you have one) might not reach as far as the big ring, so you want the BB to be as short as possible, but having enough length to install the sensor.

With the 116mm spindle, the gap was about 9mm, so hopefully I will not need to go to 122mm or higher. My Woosh kit should be delivered today, so I'll check gaps with the existing BB and the left side pedal sensor before ordering anything new.

Picked up a new Shimano BB-UN54 (68mm x 115mm) cassette from my bike store on Saturday only to discover:-

• The spindle dia is 16.8mm, (old BB was 16mm) so LS sensor will not slide over it.
  
• It has a plastic locking collar, that has tight slots, so the tags on the LS sensor will not slot in.
  

Need to pop back later to see if they have anything that will work with the LH sensor.

I can send you one if you need it.

Thanks, I'll come back to you if my cycle store cannot help.

 

Do you know what thickness spacer I need to fit behind the Shimano HG-41 7 speed cassette?

Thanks, I'll come back to you if my cycle store cannot help.

 

Do you know what thickness spacer I need to fit behind the Shimano HG-41 7 speed cassette?

4mm-4.5mm spacer. You need notches on the spacer for the rivets.

 

https://www.ebay.co.uk/itm/Cassette-Spacer/141599880918

 

Picked up a new Shimano BB-UN54 (68mm x 115mm) cassette from my bike store on Saturday only to discover:-

• The spindle dia is 16.8mm, (old BB was 16mm) so LS sensor will not slide over it.
  
• It has a plastic locking collar, that has tight slots, so the tags on the LS sensor will not slot in.
  

Need to pop back later to see if they have anything that will work with the LH sensor.

 

If you can try and buy a BB with metal locking collar. If ever you need to remove the BB later it is much easier, the last plastic one I tried removing fell to pieces and I had a great deal of trouble removing the BB.