# Spacing Hollowtech II Bottom Bracket



## TwigJumper (Mar 14, 2012)

Hello,

I am new to this, so I have a few basic questions.

I have Shimano M770 crankset with an outer chainring that I'm planning to use on my SS. 
I haven't an idea how I should apply the bottom bracket spacers to achieve the proper chainline.

Here's a link to the manual. 

It's a 68mm bottom bracket shell.

I will be running it with a rear 135mm spaced hub that is known for a 52mm chainline, according to this.


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## febikes (Jan 28, 2011)

The BB should come with three spacers. Put two on the drive side and one on the non drive side.


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## RiderInTraining (Apr 25, 2005)

febikes said:


> The BB should come with three spacers. Put two on the drive side and one on the non drive side.


Yep, what he said. The rest is done at the rear hub.


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## zaskaranddriver (Oct 14, 2009)

The crank will go together fine using the three spacers on your 68mm shell. If you don't mind your cranks being off-center relative to the frame, you can arrange the spacers differently (all three on the DS or two on the NDS, etc.) to adjust the chainline in 2.5mm increments. 

I'd try putting it together and seeing if it works in the standard configuration indicated by the posters above. You may have no issues even if the chainline is imperfect. If you get problems you can shift the chainline 5mm outboard at the crank by putting the chainring on the outside of the spider. 

At the hub you can shift the chainline outboard a little using a spacer between the hub and freewheel (making sure you still have enough threads engaged), or possibly by using axle spacers to respace the hub and then redishing the wheel back to center.


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## TwigJumper (Mar 14, 2012)

Ok. Thanks, everyone! I thought I would be able to adjust it by adding more bottom bracket spacers.


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## TwigJumper (Mar 14, 2012)

Another question: What does the spec sheet mean by "50mm" chain line? Is that the middle chainring with 2.5mm bottom bracket spacers on both sides?


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## zaskaranddriver (Oct 14, 2009)

That's the middle chainring with two DS, one NDS spacer.


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## TwigJumper (Mar 14, 2012)

zaskaranddriver said:


> That's the middle chainring with two DS, one NDS spacer.


Ah. So the chainline, using 2.5mm spacing on each side (2 DS and 1 NDS) and the outer ring, is 50mm + the distance between the middle chainring and the outer chainring, correct?

Can't I just get bottom bracket spacers from a LBS to adjust the chainline at the bottom bracket in smaller increments than the 2.5mm provided?

*Edit: See post #14. *


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## TwigJumper (Mar 14, 2012)

Should I match the spacers on both sides of the bb? 

Edit: Ignore and see post #14.


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## Thor29 (May 12, 2005)

Just put the spacers on like it was designed - 2 on the drive side, 1 on the other side. Anything else and you will mess up the bearing preload and your crank won't be centered. A 2mm difference from front to rear won't make any difference.


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## Stevob (Feb 27, 2009)

ignore. I read the link posted. It's a freewheel hub by the looks of it.


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## TwigJumper (Mar 14, 2012)

Thor29 said:


> Just put the spacers on like it was designed - 2 on the drive side, 1 on the other side. Anything else and you will mess up the bearing preload and your crank won't be centered. A 2mm difference from front to rear won't make any difference.


Wow, I had no idea putting different spacers would be that bad for the crankset.


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## TwigJumper (Mar 14, 2012)

Stevob said:


> ignore. I read the link posted. It's a freewheel hub by the looks of it.


Ignore what?


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## TwigJumper (Mar 14, 2012)

Oh, and the funny thing is, my crankset came with three 2.5mm spacers. 

Edit: Ignore this post. I though it was supposed to come with 3 different sized spacers: 2.5mm, 1.8mm, and 0.7mm. I also thought the instruction manual in the link said to have 2.5mm on each side: 2.5mm on the NDS and 1.8mm + 0.7mm on the DS, hence my confusion of needing equal amount of spacing on each side. 
I now see that it shows to put one 2.5mm spacer on the NDS and two 2.5mm spacers on the DS, like what you all have been saying. I just didn't catch the size of the spacers you all and the instructions said to use. :embarrassed:


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## mitzikatzi (Sep 9, 2008)

Huge Zits said:


> Wow, I had no idea putting different spacers would be that bad for the crankset.


Thats not true IMHO.

Agree about 2mm difference in chain line not making much difference if you use a multi speed chain.


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## blackgriffen_1 (May 18, 2010)

To clear things up: technically, any external bottom bracket should only be used with the number (or rather, total width) of spacers that it's designed to be used with, otherwise as mentioned before you risk screwing with bearing preload and attachment of the non-drive side crank arm to the spindle. I have hollowtech too, and to move the chainline out you could throw all three spacers on the drive side, but if you have a freehub wheel that allows you to move the cog back and forth with spacers on the freehub body, just install the bb the way it's supposed to be (2 DS, 1 NDS), and you'll be golden. :thumbsup:


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## Stevob (Feb 27, 2009)

Huge Zits said:


> Ignore what?


ignore my first attempt at a reply by saying that it's better to use the rear to adjust the chainline.


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## RiderInTraining (Apr 25, 2005)

It's funny that we're still posting to this thread. In case you couldn't find the Shimano instructions for your crank set, the first reply to your post already answered your question about how many spacers to use on what side.

On the rear hub you use spacers to line your cog up with the chainring. I just eyeball it before I put a chain on until it looks OK. Never had any problems.

I don't understand why you make it so complicated... you could already be out riding.


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## TwigJumper (Mar 14, 2012)

Thank you for all the replies, everyone! I'm now more confident in deciding what to do. 

I'm a noob and this thread was all about getting the perfect chainline and the proper way of doing it. I made a big fuss over it since I just spent a good amount of money on parts and wanted to see how to get the chainline right the first time. 

Again, thank you, everyone! I am grateful of every single reply. 
I now know that it is recommended to use the correct amount of spacers for the bottom bracket and that it is safe to put a little spacer behind the Shimano MX30 sprocket, though a perfect chainline isn't too important. 

I hope others who come across this thread from the search function find this helpful.


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## giverpig (Dec 20, 2004)

I came across it and it was helpful


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## Jumble (Jan 28, 2015)

Yeahp.. Three years later - this info was still helpful. Thanks!


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