Mountain Bike Reviews Forum banner
1 - 12 of 12 Posts

·
Registered
Joined
·
247 Posts
Discussion Starter · #1 ·
I have a set of 2007 XTR 970 cranks/bb. I know the last batch of XTR bb's had a pretty long break in period with respect to the bb spinning. I was under the impression that the new models were supposed to spin pretty well, especially with that nifty little adjustment for the pre-load. Does anybody know how long the break in period is? The drag is outrageous. Thanks
 

·
Vaginatarian
Joined
·
5,686 Posts
I think all the external BB drag, how could they not? when you push the axle through the bearing, the dust seal contacts the axle. even on a perfectly aligned set of bearings that means you have 2 rings of plastic contacting the axle and creating friction. if the alignment is off, more friction. after they wear, the friction will decrease but I dont think its noticable (at least on my xts over a year).
 

·
Super Moderator
Joined
·
20,810 Posts
dan0 said:
I think all the external BB drag, how could they not? when you push the axle through the bearing, the dust seal contacts the axle. even on a perfectly aligned set of bearings that means you have 2 rings of plastic contacting the axle and creating friction. if the alignment is off, more friction. after they wear, the friction will decrease but I dont think its noticable (at least on my xts over a year).
Yeah.. I have external bearing XTs and Hone cranks.. and I don't notice any friction while riding... but a lot of people care about drag "on the bikestand"
 

·
the catalan connection
Joined
·
1,266 Posts
woogie11 said:
I have a set of 2007 XTR 970 cranks/bb. I know the last batch of XTR bb's had a pretty long break in period with respect to the bb spinning. I was under the impression that the new models were supposed to spin pretty well, especially with that nifty little adjustment for the pre-load. Does anybody know how long the break in period is? The drag is outrageous. Thanks
Just some thoughts:

Does the drag get any better taking some preload off from the bearings?
Could be that is too cold+new grease not relocated yet as the bearings push it aside?
Is drag equal allover the spin cycle?If not, I would suspect there is something missaligned,or missassembled, or missmanufactured.
Have you replaced the rear hub too(or freehub)? I have just repacked some grease in my freehub and the drag is really strong. But does not make the chain loose much tension on the chainstay upper side when coasting(or back pedaling at the stand). BTW, that would be the an easy way to discerne wheter drag comes from cranks or freehub, in case you doubt.

These are the things that came to my mind.No expert, just seen them happen sometimes.
 

·
the catalan connection
Joined
·
1,266 Posts
dan0 said:
I think all the external BB drag, how could they not? when you push the axle through the bearing, the dust seal contacts the axle. even on a perfectly aligned set of bearings that means you have 2 rings of plastic contacting the axle and creating friction. if the alignment is off, more friction. after they wear, the friction will decrease but I dont think its noticable (at least on my xts over a year).
The dust seals contact the axle but they turn with it (along with the O rings). There is, in practice, the same friction as when you turn the bearings with you fingers with the axle removed. But in theory, there should be a slight increase in friction as the whole thing becomes a bit more tight as the axle is pushed throug.And even more if you preload the system too much.
If the bearings are well aligned (faced shell),and propper preloaded,I thing the system should not show any more drag than any other.
 

·
TranceX Rider
Joined
·
948 Posts
Mine's as well... The old M-960 also... Didn't give me any headaches like yours... Even at the 'break-in' period.


OT: can you somehow post pix what you've/ or your friendly LBS used to install it... Since I learned that it has a special tool for installation. Haven't got a peep while... Thank you.
 

·
Vaginatarian
Joined
·
5,686 Posts
What&son said:
The dust seals contact the axle but they turn with it (along with the O rings). There is, in practice, the same friction as when you turn the bearings with you fingers with the axle removed. But in theory, there should be a slight increase in friction as the whole thing becomes a bit more tight as the axle is pushed throug.And even more if you preload the system too much.
If the bearings are well aligned (faced shell),and propper preloaded,I thing the system should not show any more drag than any other.
I have a brand new cup & bearing set in my hand. Youre right when you say the whole thing turns together, but , it doesnt turn easily. bear in mind that its not even installed so no axel/ facing/ preload issues. I dont think its that much of an issue, but I notice when I take my chain off and spin my cranks, the external bb 5or 6 times, my other bike with an internal bb spins 20-30 so there is alot more drag with the external system, this was confirmed by my Lbs and by my own method on several bikes. You can see it when you first install before you preload, give the cranks a spin , how many revoloutions?
 

·
the catalan connection
Joined
·
1,266 Posts
dan0 said:
I have a brand new cup & bearing set in my hand. Youre right when you say the whole thing turns together, but , it doesnt turn easily. bear in mind that its not even installed so no axel/ facing/ preload issues. I dont think its that much of an issue, but I notice when I take my chain off and spin my cranks, the external bb 5or 6 times, my other bike with an internal bb spins 20-30 so there is alot more drag with the external system, this was confirmed by my Lbs and by my own method on several bikes. You can see it when you first install before you preload, give the cranks a spin , how many revoloutions?
You´re right,afterall are larger bearings, so more drag is to be expected.But I have seen outboard bearing cranksets spin freely too.But in the sense that it had that feel of running out of grease. So, I just think is a matter of grease and seals impregned with it when new.
They are serviceable (bearings accessible) not easy, but doable, so they can be packed with lighter viscosity grease for the winter.
 

·
Vaginatarian
Joined
·
5,686 Posts
What&son said:
You´re right,afterall are larger bearings, so more drag is to be expected.But I have seen outboard bearing cranksets spin freely too.But in the sense that it had that feel of running out of grease. So, I just think is a matter of grease and seals impregned with it when new.
They are serviceable (bearings accessible) not easy, but doable, so they can be packed with lighter viscosity grease for the winter.
do you think its the grease? its not temp. related as the bikes and bearings I have access to are all indoors.I thought I was doing something wrong initially, because the cranks just didnt spin freely like my internal BB did, I've replaced the crank bearings with enduro bearings but didnt notice any better spinning. for me its not an issue, but I could see racers and distance riders not liking it
 

·
the catalan connection
Joined
·
1,266 Posts
But you know that smooth spinning and drag free are not the same thing. Every king hub owner reports on how smooth they roll but also on how big is the drag.
Besides the grease and the seals there is no other source of drag I can think of. Grease will be pushed aside as the bearings rool over it for a while, the seals will also clean the grease around them, the bearings and races will make the final matching, and I´m sure after a couple rides the thing will roll perfect.
If they will roll as drag free as a smaller bearing BB I would say probably no, as they are a larger setup. But sure they can roll as smooth.
 
1 - 12 of 12 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top