Bicycle Mechanics - ISIS Crank Question

I took apart my ISIS crank and bottom bracket on my Surly 1x1 for cleaning today. When reassembling, I looked up the torque spec for the ISIS crank bolt and it said to bottom it out (30 to 50 ft-lbs). I did this on the drive side and the crank began rubbing on the bottom bracket (where the 20 tooth splines are on the cup). Do I have a mismatched crank and bottom bracket? --- Crankset is RaceFace Prodigy XC and bottom bracket is RaceFace SRX 108mm.

I don't have a torque wrench and I am worried about under or over torqueing my cranks on my ISIS BB as well...I am curious, is 30-50ft-lbs...-like, 'a lot' ? Is it a 'manly' amount of torque? -(when using extra long allen key) ?

Yeah -- 40 ft-lbs is really tight. It's 40 pounds of force on a wrench 12 inches long. That would be a pretty heavy tug.

I don't have a torque wrench and I am worried about under or over torqueing my cranks on my ISIS BB as well...I am curious, is 30-50ft-lbs...-like, 'a lot' ? Is it a 'manly' amount of torque? -(when using extra long allen key) ?

The deal with torque is it could be "manly" or "whimpy" - it all depends on how long the wrench is. Remember, for 30 ft-lb is equivalent to a 30 lb force acting on a 1 foot lever arm.

30 ft-lb could be any of the following values:

120 lbs with 4 inch lever (manly)
8 oz with 60 foot lever (whimpy)

Basically, 30 ft-lb is typically hard to achieve with an 8mm allen key. Personally, I use 3/8" socket drive Allen bits with standard socket handles.

The deal with torque is it could be "manly" or "whimpy" - it all depends on how long the wrench is. Remember, for 30 ft-lb is equivalent to a 30 lb force acting on a 1 foot lever arm.

30 ft-lb could be any of the following values:

120 lbs with 4 inch lever (manly)
8 oz with 60 foot lever (whimpy)
...

I dunno man - I wouldn't call any man with a 60 foot lever "wimp." ;p

I dunno man - I wouldn't call any man with a 60 foot lever "wimp." ;p


;) > :rolleyes: > :eek: > :D

I took apart my ISIS crank and bottom bracket on my Surly 1x1 for cleaning today. When reassembling, I looked up the torque spec for the ISIS crank bolt and it said to bottom it out (30 to 50 ft-lbs). I did this on the drive side and the crank began rubbing on the bottom bracket (where the 20 tooth splines are on the cup). Do I have a mismatched crank and bottom bracket? --- Crankset is RaceFace Prodigy XC and bottom bracket is RaceFace SRX 108mm.
I would suggest calling up the Manufacturer and telling them about what happened. Also, is inch/lbs or ft/lbs? Big difference. Lots of bike parts use the in/lbs spec, be careful.

Tim

It's definately 30 to 50 ft-lbs for the crank bolts (or 360 to 600 in-lbs) in the instructions. This is about what it takes to "bottom out" the crank which is also part of the instructions for a RaceFace X-Type crank bolt. Since my chainline is short in the front anyway compared to my Surly 1x1 hub I've decided to try a longer bottom bracket (118mm) and see what that does.

Typical manufacturer's crank arm installation torque recommendations (square taper, ISIS or Octalink) are 300 to 400 inch-pounds which is the same as 25 to 33 foot-pounds so 30 ft-pounds is in the correct range.

It sounds like you have the wrong bottom bracket length, at least for the frame you are using.

http://img342.imageshack.us/img342/5839/crankbb6nb.th.jpg (http://img342.imageshack.us/my.php?image=crankbb6nb.jpg)

I have the same problem....looking for answers.

I just finished re-building my 10yr old klein with newer parts.
Using Shimano LX octalink cranks w/ XT BB (118 wide).

When I installed the crank (with rings) the small chainring was rubbing on the BB shell.
I backed it off a little, put on the chain and began to adjust derailers.
The chainrings were so close it wouldn't drop to lowest ring.
I removed then re-installed the crank and tightened just to the point where the chain would fall onto the smallest chainring, the rings still seem very close to BB but it works (at least on the stand).

The problem, other than it's still to close the BB, is I'm not sure how safe it is to ride with a crank only half-way inserted.

The problem, other than it's still to close the BB, is I'm not sure how safe it is to ride with a crank only half-way inserted.

It won't be unsafe for very long. If the crank isn't installed properly on the bottom bracket axle, it will rapidly loosen as you ride and the steel axle splines will tear up the Al splines in the crank arm. Result; trashed crank. Don't do it.

You need a longer bb spindle or a different model crank.

Shimano doesn't make a BB wider than 118mm.
The original LX square taper BB was 113mm.
I even measured each.

I guess the newer splined stuff just squeezes tighter. :(

Actually it's probably about 3/4 engaged.