Re: Bottom bracket sizing problem
- From: "Clive George" <clive@xxxxxxxxxxxxxxxxxx>
- Date: Tue, 31 Jan 2006 17:01:09 -0000
"Rob" <mr_horton@xxxxxxxxx> wrote in message news:1138722835.102340.224510@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
I have an old steel specialized rock hopper that I use as my about town bike. The bottom bracket (not the original) is now about to fall apart. It is a UN72 for 73mmm shell and the spindle is stamped 110E. Measuring with the vernier claipers I get 111mm, so I guess its about right.
About a year ago I purchased what was probably one of the last square taper LX chainsets as the specialized chainset had finally died. Since then I have noticed that the lefthand (non drive) crank is approx 5mm further away from the chain stay than the righthand crank. That is 15mm gap for the left and 10mm for the right when measuring from the inside of the crank along the middle of the peddle spindle to the chainstays.
What can I do to make my cranks my symmetrical?
Do I buy a 107mm spindle or a 113mm spindle?
How do I know that the length variation will only affect the left hand side?
Are there any decent engineering drawings that show the dimensions of shimano BB's?
The 73mm and 68mm shimano BBs are almost the same - the difference is in the shim which goes on the end and an extra 5mm on the LHS spindle.
I've used this to my advantage on our tandem - different LH and RH cranks need different spindle lengths, and fortunately it's the LH one which needs to be longer.
Anyway it sounds like you've got a similar thing here. If you put a 113mm long 68mm BB in with the same shim as you've got now your LH will move in 4mm and your RH out 1mm, and all will be about right.
cheers, clive
.
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