Jhartman1

Hi, I am looking at some mountain bike frames to transfer my older xt crankset from my current frame. The current frame is a GT that uses a 68 mm bottom bracket. Similar to an ultegra BB-6500. How do I know if I can transfer it over?
Thanks, Jeff
Juneau, Alaska

JiveTurkey

Frames can take either the internal or external bearing BBs. Within the English threading standard, there are 68mm and 73mm wide shells. Get the matching BB to the crank and ensure it'll work with the shell width.

Jhartman1

Thanks, Naturally one question leads to another. The mountain bike frames I am looking at all have English threads My crankset is a hollowtech II xt that fits a Shimano BB-6500 68 BC 1.37x24 with a width of 118.5. I suspect it will fit any shimano splined BB. What do all those numbers mean? I thought the 68 was the diameter of the bottom bracket, but my calipers say it is much smaller than that.
Thanks, Jeff
My son lives in Portland and goes to PSU

bikeman715

68 is the width of the bottom bracket . 118.5 mm is the width of the axle running thou the BB . the 1.37x24 is the treads inside of the BB .(how many treads per square inch ) .

HillRider

If your crank is a Shimano XT, it will not work with the BB-6500 Octalink bottom bracket as the splines are different. Shimmano's road cranks and the XTR MTB crank use the V-1 version of the Octalink. All the other Shimano MTB cranks (and Sora road cranks, IIRC) used a different V-2 Octalink.

Jhartman1

Okay, Patience because I am a little confused. I have the BB-6500 in my left hand (the one with the numbers I just listed in the earlier post) and my XT FC-751 crank arm in my right hand, they both have 8 splines and the crank arm fits right in the splines. I tried threading it on with an allen wrench and the threads fit perfectly. What am I missing?

fietsbob

external bearing and a tube bb axle are a set, the spindle is part of the right crankarm.

internal BB type is a separate set, the scheme is both arms fit onto a central movement.

in essence 3 pieces, external is 4 , the 2 bearings and the right side combo + the left arm.

pretty much apples and orangoutangs ..

HillRider

The spline length on the MTB (V-2) Octalink is greater than on the road (V-1) version. Also the V-2 splines are slightly wider so your crank will indeed slip onto a V-1 the spindle but the support in both length and width won't be correct. Look here for a illustration of the differences:

https://www.sheldonbrown.com/bbsize.html#shimano

well biked

Hillrider's already answered with the pertinent info, but I'll add that if you were to assemble the parts you describe above (V1 bb w/ XT Octalink crankset), after the first ride the crankset will be ruined. I worked on a bike not long ago where the owner had done just that, and when the bike came in it seemed that maybe the freehub body wasn't engaging because when you pedaled the bike there was a big delay until the drivetrain engaged. Nope, after some checking, with the V1 bb and V2 Octalink crankset installed, the aluminum splines on the crankset had distorted and sheered enough that the crankarms were barely hanging on and the problem was causing the symptom I described. Another ride and the crankarms would have likely come off completely.

bleukahuna

First off, you do NOT have a HollowTechII crank set, these are all 2pc external bearing crank sets. You have a FC
M571, an Octalink system. If your FD is frame mounted you need a BB-ES50, if you actually have a 68mm shell, you would need a 113mm spindle. Amountain bike is more likely to have a 73mm shell that would call for a 118mm spindle length. If your FD is bottom bracket mounted would need the BB-ES50-E and the same spindle lengths.

Jhartman1

Thank you all. You've solved several mysteries for me. I am humbled by my ignorance. Hillrider, your right, the spline lengths are clearly different. I pulled out the old bb-ES70 that was on that bike and the splines are much longer. Well biked, I needed your example to explain why that was important. bleukahuna your right too. I saw hollowtech on the crankarm and thought it must be hollow tech II, and that the scratches were just blocking it out. The old bb-es70 is 118 mm. Most importantly I know now that if I find a mountain bike frame I like, I should be able to adapt most the stuff I have from my 2001 GT. I may need to get a different length of shimano bb, or change the FD clamp. Oh, also I had forgotten why I had that BB-6500. I bought that to replace on one of our road bikes 4 or 5 years ago. Now I realize it isn't compatiable with any mountain bike frames I would consider. Again, thanks. Jeff

Matt Gaunt

This thread is a shining example of the wealth of knowledge at BF. I enjoyed reading it a lot and found out some stuff that I've wanted to know for a while. Thank you.

HillRider

If your BB-6500 is still unused, it should have some significant value. It was the optimum Octalink road crank as the 105 (BB-5500) was heavier and the Dura Ace (BB-7700?) was smoother and lighter but required frequent maintenance.

Shimano no longer makes the BB-6500 or Dura Ace Octalink bottom brackets and the BB-5500 is the only current one so a new or nearly new 6500 is a derirable component and should sell easily.

Jhartman1

Hi HillRider, Yes the BB-6500 is new in the box and never mounted. I am not sure if it is the right size for my sons cannondale R600 or my mid 1990s bianchi alfana. I know the alfana is a 105 (not hallow tech II). Also, it might fit my Bike Friday Pocket Rocket which also uses 105. If it is isn't the same length as one of those, I will put it on the selling block. Thanks, Jeff

Iowegian

One nice thing about the Shimano road Octalink BB's is that they all use the same size(s). 109.5mm for doubles and 118.5mm for triples. So the only concern about whether or not it will fit is that you need to match the number of chainrings to the BB length.

Jhartman1

Thanks, I didn't realize that either. All three of them are triples. So I will keep it for a spare. Jeff