BB spacing query/On One frames

lvquestpaddler

Hi,
I'm giving serious consideration to buying either another 16" Inbred or a 456 in steel. The rigid I built up recently(inbred) will be used for fast xc and light touring, so I may get a 456 as this gives a bit more options(ie bigger forks)- at present it would get all the bits off my GT Avalanche with 100mm Toras.
When I built the rigid I got a 113mmx68 octalink BB and acera M341 cranks off ebay- all new and good enough for my useage- but when I put it all together there were issues with clearance of the chainset and rings and the stays. In a nutshell I had to grind off the crank inner ring fittings as they fouled the chainstays, the 32T( its a 1x9) had to go on the outer side of the chainset and even at that it still just clears the frame.
If I buy a new frame it will be for a 1x9 so the old GT has a 73x118 BB(same octalink and same cranks), which I was wondering could I put this BB on a 68 shell if I spaced it out? If I put a 2.5mm spacer either side of the shell this makes it 73(?) and would make the spindle 5mm wider than the current 113 on the inbred?(118 plus 5=123 so difference divided by 2=5mm?) If that wasn't enough could another 2.5mm be added to them to give 7.5mm extra?
121mm BB's seem cheaper on ebay maybe a new one of them would be better altogether it would put the chainset 4mm further out- but there are real clearance issues and I'm not the only one judging by the questions asked on their site- the stays come out at a pretty sharp angle at the back of the BB shell....
Ta!

nicklouse

with those cranks you should have used a bb with a 126mm axle

lvquestpaddler

Hi Nick- is that because they're crappy Acera spec? Is that not huge? On one seem to recommend 113 or is that only suitable for deore and above?
I'll have a search for that size! Is this to keep the chainline at 50mm or something? It will be a single so using the outer side of the crank isn't a problem if I use a narrower one- but that means any notion of going 22/36 or something is out the window as the middle won't get used.
Is this an issue with most chainsets?
Cheers

nicklouse

no it is because that is what will give the correct chain line.

113 fits different cranks and designs.

using the ring in the wrong position can cause issues needing a file to be used.

and not if you use the correct parts.

lvquestpaddler

The biggest ES51 octalink for a 68 seems to be 121mm(73 is in 126?)? The UN54 square comes in a 68x126 but that would mean getting new cranks too.
Is it possible to get spacers for these BB's or are they just for external BB's?
Thing is Nick- if you can find this info(thanks for doing it) I wonder why are On One so vague about what they recommend BB wise. I've asked them via their online questions what would be needed if I went back to a triple set up using the M341's. Wonder what they'll say!?!

davewalsh

On-One probably won't say anything other than the frame takes a 68mm BB and is designed for a 50mm chainline. Axle length has nothing to do with the frame, it all depends on the chainset. You need to be asking Shimano which axle length is required for your chainset to give a 50mm chainline.

FWIW I have 2 inbreds, both running triple's, one has a FC-M442 chainset and 113mm axle, the other has a FC-M521 chainset and 121mm axle. Both fit perfectly with no clearance issues.

davewalsh

Shimano tech doc here:
http://techdocs.shimano.com/media/techd ... 616270.pdf

You need a 118mm axle.

nicklouse

davewalsh wrote:

Shimano tech doc here:
http://techdocs.shimano.com/media/techd ... 616270.pdf

You need a 118mm axle.

but that does not list the 431-8 as suitable for a 118mm axle.

this
http://techdocs.shimano.com/media/techd ... 621467.pdf
lists the 126mm axle as suitable for the M431-8

davewalsh

nicklouse wrote:

but that does not list the 431-8 as suitable for a 118mm axle.

The OP has a 341 not a 431.

Edit: Looks like you're right. The tech doc that you have linked is clear that a 126 axle is needed.

lvquestpaddler

Cheers for this will try and open the techdoc in adobe- my G Chrome is only opening it as a "snapshot" and can't zoom in on it...
Learn something new every day!! 8)

lvquestpaddler

So what difference does the chainring make? The one I put on it was a Gebhardt alloy one from velosolo- should I change that to an M410 steel job and use a 118mm to give the correct 50mm chainline- and this means the chainring goes back to the inside of the crank? Would an M510 make any significant difference.?
The problem I'm seeing is that by adding 2.5mm either side(assuming going from 113>118 does this) is nothing. If the cast bolt holes for the inner ring were colliding with the chainstay- and by colliding I mean had I tightened it up fully the cranks would not turn- they were hitting just pushing the crank on to the end of the BB by hand. So this is without the 22T inner even on the crank which adds some considerable distance to the radius.
:? :? :?

davewalsh

The chainrings don't make any difference, it's all to do with how far the axle goes into the splined hole in the chainset. Going to a 126 axle with the chainring on the inside will give you the correct chainline.

CRC do an ES25 BB in 68 x 126 for £12.99
http://www.chainreactioncycles.com/Mode ... elID=34653

Going back to your original post, are you sure that the GT has the same cranks with a 118 BB ?

lvquestpaddler

The GT has a 73x113 as OE- ISIS with FSA cranks. I've measured the chainring on my On One and to the centre of the seatpost it's bang on 50mm. Luck!!
I've just measured the GT and it now has a chainline of 45mm so will need a bit of fettling to get it to 50mm. A 126 BB would get it to 49mm close enough?
Maybe thet's why the ON One chain stays on the chainring without a guide and the GT jumps off with rapid upshifting?
So- can an "internal" BB like this be spaced by putting spacers between it and the frame?

nicklouse

So- can an "internal" BB like this be spaced by putting spacers between it and the frame?

No, you need the correct BB.

lvquestpaddler

I've ordered an ES25 at 126mm for the GT, hopefully this will make things better on it- I was having issues setting the derailleur maybe this is why?
On the On One I'm happy with the setup and it looks neater with the chainring on the outer. Will this reduction in "Q factor" of 13mm overall make any significant difference?

nicklouse

what have you fitted? to what size BB shell? what chain line do you have now?

octalink BB or ISIS or......

lvquestpaddler

I've bought the new ES25 73x126 for the GT Avalanche trainer. Just fitted it and re-adjusted the front mech and it's all working perfectly- measured the chainline it's 50mm as it should be, I now have it set perfectly as a 2x7. If I want a bigger chainring(42) adding this at a later stage won't now be an issue. All went well apart from turning the shed inside out and still failing to find the crank extractor- had to bodge it with an old Park square specific one and some washers I found in the shed. Still not found it!

The on one(1x9) also has a 50mm chainline and happy with this- but that's with the 32t on the outer(42t) position, a fluke. I was wondering if that reduction in axle(from a 68x126 also to 68x113 actual) would be significant in narrowing the setup?
Suppose with the same cranks on both bikes I could just see how they both feel compared to each other.... 8)