[bayarearider]

I will try and describe this the best i can.

Here is the problem i am having......i am trying to swap cranksets on me SS. It currently has a old school suntour crankset with a square tapered older LX BB (68X113).

I had an extra XT crankset with XT BB (68X113) laying around so i decided to install it.


For some reason when i try to install the left arm and begin to torque it, it starts to rub on the BB shell ( not sure what this part is called). I think i need about 3 mm of more space and it will be ok.


But the crankset side fits perfectly with no rubbing.

Am i not getting something?

i would say i am a little more advanced than a beginner when it comes to fixing bikes. I've installed several cranksets before and have never ran into this problem. any ideas?

When i line up the two BB they look the same length.

 

[Speedub.Nate]

If it's an older XT crank -- early 90's -- you'll probably need a longer spindle. 118mm would be my guess. You can easily verify this by torquing down your driveside arm on the currently installed bottom bracket and measuring the chainline from the center of your frame tubing to the tip of any tooth on the middle ring. If it's less that 47-48mm, spindle length is too short.

Another possibility is a rounded non-drive side taper that's allowing the arm to be pressed on too far.

Yet another possibility is the non-drive side adapter cup isn't torqued properly and is sticking out too far, causing interference. In the case of Shimano cartridge bottom brackets, the adapter can be torqued to the same max 36 ft-lbs as the drive side.

 

[bayarearider]

Speedüb Nate,

The crankset isn't too old, it's the m751 with xt BB. I'll install the crankset again and take the measurement anyway.


I am not sure i get what you are saying about the rounded taper. How does this usually happen and what is generally the fix?

Also i am 95 % sure the BB is properly torqued.

I'll try and get some pictures up when i re install it tommorow night.

thanks for the reply!

 

[Speedub.Nate]

Ahh, never mind that thing about the rounding -- I made the assumption it was an old square taper XT you were installing.

Rule of thumb for Octalink installations is to bump up a spindle length over what you were using with a square taper. So my guess is your 113 Suntour setup got you 50mm spacing, which is what a 118mm Octalink spindle would get you.

But that doesn't address why you're getting non-drive side crank arm interference, and the only real suspect there is that you're trying to install a 68mm cartridge into a 73mm shell. Have you measured the width of your frame's bottom bracket shell to verify it is indeed 68mm?

 

[bayarearider]

i will take the measurement the shell just be to be sure. I assumed that the 68 XT would fit since the old LX square taper was a 68 also. Thanks for all the advice speed...i'll post what happens

it's a old trek 930 ...if that helps

 

[Speedub.Nate]

Most Treks are 68mm shells but I did find an online reference to a 1999 Trek 930 with a 73mm shell. Worth checking out. That's the only suspect as to why this doesn't work -- otherwise, a 68x113 Octalink & XT crank should have no trouble fitting this frame.