** Bottom Brackets - What's Correct? **

[velofrog]

Just fitted a new Shimano BB93 bottom bracket for their hollowtech cranks to my Black Sheep.

I know the rule of thumb that with a 68mm shell two spacers go on the drive side and one on the non drive side and for a 72mm shell it's one on the drive side and none on the other.

Now, to get the chainring to clear the chainstay i've had to put all three on the drive side. :shock:

I'm using this singlespeed so the XTR 9020 crank has a 32 tooth Absolute Black oval ring fitted, and it would seem there is no way a 34 tooth would clear without hitting the stay, the 32 however does clear.

The thing is, when checking the crank arm spacing against the stays they are near as damn it perfect left and right.... so I'm presuming three spacers on the drive side is ok?

Just worried about torque load on the cup as there's a couple of mm less threaded into the shell on the drive side....

Your opinions please gents!

 

[velofrog]

Re:

EDIT:

I've just checked my front chainline which is apparently supposed to be 52mm for SS MTB from centre seat tube to centre chain and it is cock-on 52mm, so at least that's ok! :?

 

[ishaw]

Re:

The BB shell on that frame looks pretty darn wide. Don't want to ask a silly question but is it wider than 73mm, possibly an 83mm one? Might explain why you've got clearance issues when using a crank/axle with a 73mm max length?

 

[velofrog]

Re:

silly questions are allowed, but it's only 68mm wide!

 

[FluffyChicken]

Re:

They run crank arms a long way away from the stays nowadays.

While it might be wrong and I assume you followed the Shimano Documents for fitting the crank and BB etc.

If it works, use it

 

[klunkrider]

Re:

I’d be wary about how much thread will be engaged with that many spacers on one side.

 

[velofrog]

Re:

I know, that's why I was asking, not too sure myself. :?

I guess I could install a 2.5mm spacer between the spider and the bearing, slip it on the axle before I push it through the bearing cup?

That would give me the same distance but only two spacers between the cup and the BB shell?

Shall have a rummage through my spares and see if I can find anything suitable, if not I may ask on here if someone could turn something down for me.

 

[velofrog]

Re:

just got this on ebay... perfect for the job

https://www.ebay.co.uk/itm/BBB-BBO-91-S ... SwoR9aBGqg

 

[bolly]

Some new bottom brackets have longer threads designed for chain devices have a look on chain reaction shimano saint hollow tec two on offer £15 as an example explains it in the description

 

[velofrog]

Re:

Thats a great shout, if I didn't already have a new BB93 I'd have snapped that up!



EDIT: in fact for £15.99 i'd be stupid not to... off to log in to CRC