Powerspline BB question

My daughter's partner is a daily commuter into central London and does give his bike a bashing. He has been complaining about his cranks wobbling so I said I'd change the BB. It is truvativ crankset with a Powerspline BB, and in my bottomless pit of spares in the shed I had a spare, almost new one.

One problem is the original was a 108mm and the new one is 113mm. I have fitted it, the chainline is unchanged and the bike rides and changes gears perfectly, but the left crank is now 5mm further out from the frame. I don't think there is a problem with this but will the fact that the left cup now stands 5mm out from the frame weaken it at all?

I have also changed the big ring and the chain as the old ring was like a ninja star. The rear cassette was almost new.
 
Location
Loch side.
If the cup sits proud, you've fitted a 73mm BB to a 68mm BB shell. If it was just the spindle that's too long, there will be no excess thread on the BB itself.

Basically it sounds as if you've put a MTB BB onto a road bike. Is that the case?
 
If the cup sits proud, you've fitted a 73mm BB to a 68mm BB shell. If it was just the spindle that's too long, there will be no excess thread on the BB itself.

Basically it sounds as if you've put a MTB BB onto a road bike. Is that the case?
Probably yes. I seem to remember the new BB originally came with a spacer for use on a 68mm which has been lost. My question still stands about the acceptability of this arrangement.
 

chriscross1966

Über Member
Location
Swindon
Probably yes. I seem to remember the new BB originally came with a spacer for use on a 68mm which has been lost. My question still stands about the acceptability of this arrangement.
It will likely fail, possibly catastrophically for the rider and probably for the frame, and fairly quickly too. You've effectively left one end of the BB floating on its threads rather than being tightened up hard against the bracket tube.
 
It will likely fail, possibly catastrophically for the rider and probably for the frame, and fairly quickly too. You've effectively left one end of the BB floating on its threads rather than being tightened up hard against the bracket tube.
Yikes! Back to the drawing board.

I will have to dig out that spacer or find another one to use on a 68mm wide BB.
 
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I can't agree more. Absolute rubbish.


This one will be kept for as long as it's going round and round smoothly as that's what BBs are for, and it was free.

If or when it stops working smoothly (after buying his bike second-hand this one has been used daily for six years before packing up) I will ask him if he wants it changed for the same again for about £12 or does he want to change the crankset and BB at a lot more than £12. He does not cycle for pleasure, and is commuting in all weathers, wearing working clothes, on an old bike, not worried about beating his PB and probably would not notice the difference between a Shimano or FSA BB.
 
Location
Loch side.
This one will be kept for as long as it's going round and round smoothly as that's what BBs are for, and it was free.

If or when it stops working smoothly (after buying his bike second-hand this one has been used daily for six years before packing up) I will ask him if he wants it changed for the same again for about £12 or does he want to change the crankset and BB at a lot more than £12. He does not cycle for pleasure, and is commuting in all weathers, wearing working clothes, on an old bike, not worried about beating his PB and probably would not notice the difference between a Shimano or FSA BB.
No-one is denying your rights to do what you want. Also no need to justify what you did or will do or will pay.
My comment concerns the technical qualities of the product.
 
No-one is denying your rights to do what you want. Also no need to justify what you did or will do or will pay.
My comment concerns the technical qualities of the product.
I know no-one was denying me the right to do anything, and I suppose I was responding more to the post of @cyberknight that you agreed with....."FSA powerspline ? I would change the crankset to something else TBH"....explaining why I wouldn't in this case.

There are times when I will go with the best technical solution and others with the cheapest and most convenient as long as it does the job.
 
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