A little bottom bracket help please....

[Hovis_loaf]

Re: Re:

What does the (1.)37 x 24 signify then?

Cup type/size: English threaded...1.37" cups x 24 threads per inch.

With regards to your link to Chain Reaction; Shimano ES51 Octalink Bottom Bracket is the V2 version - here is a list of some models, and more importantly, the difference in the Spline dimensions, which are not interchangeable:

• Octalink ® V1 Spline: BB-M952 (XTR), BB-7700 (Dura-Ace), BB-6500 (Ultegra), BB5500 (105)
V1 BB spline grooves 5 mm long, ridges 2.2 mm wide.

• Octalink ® V2 Spline: ES70/71, ES50/51 (Deore XT M571/572, Deore LX M751/751, M510-8, M440-8, also 2005 Tiagra FC4401 & 4404, 2005 Sora FC-3001 & 3004)
V2 BB spline grooves 9 mm long, ridges 2.8 mm wide.

Edit: BTW 36x24 is Italian thread 36 mm x 24 TPI

Pip

Hi Pip,

That was super helpful thanks, made a lot more sense with the 1. in there.

So will the unit suggested by legrandefromage work? It doesn't specify whether it is English or Italian thread in the eBay ad but I have found it on Chainreaction
https://www.chainreactioncycles.com/shi ... rp-prod906 and you can select either of the thread types.

Mark

 

[klunkrider]

I'd say the first thing you need to do is measure your bb shell and determine whether you need a 68 or 73mm bottom bracket.

Just from your image I'd say that 'looks' like a 73mm bottom bracket but obviously I could well be wrong. If it's 73mm then forget about using a road bb, they'll all be 68mm.

In terms of axle length, if you go longer then you don't have to worry about your chinrings or crank arms hitting the frame but obv you don't want to go too long.

 

[Hovis_loaf]

I'd say the first thing you need to do is measure your bb shell and determine whether you need a 68 or 73mm bottom bracket.

Just from your image I'd say that 'looks' like a 73mm bottom bracket but obviously I could well be wrong. If it's 73mm then forget about using a road bb, they'll all be 68mm.

In terms of axle length, if you go longer then you don't have to worry about your chinrings or crank arms hitting the frame but obv you don't want to go too long.

Hiya,

You are quite right it is 73mm! I am pleased you mentioned that as I hadn't though about it at all and I would have just bought a 68!

It is proving a little more difficult than I was expecting. Sorry if this is a stupid question but I am going to ask it as I do not know the answer for sure. Is a 68mm bracket be a complete non-starter, I only ask because I had a spacer on my existing bb, it is 3.5mm which gets me closer to the 68mm. Or will this completely screw up the alignment, or just not engage properly etc?

 

[ishaw]

Re:

The xtr version was designed to work with 68 or 73mm bb shells, with spacers taking up the gap. Iirc, one spacer was needed on 73mm shells, 3 on 68mm ones.

I 'may' have a spare one, need the check though.

 

[Hovis_loaf]

Re: Re:

The xtr version was designed to work with 68 or 73mm bb shells, with spacers taking up the gap. Iirc, one spacer was needed on 73mm shells, 3 on 68mm ones.

I 'may' have a spare one, need the check though.

I don't think I understand. If I get a 118mm in place of the 116mm I could get a 68mm version to work?

 

[ishaw]

Re:

It's the cups that need spacing, enough thread in the frame.

 

[Pipmeister]

Re:

The xtr version was designed to work with 68 or 73mm bb shells, with spacers taking up the gap. Iirc, one spacer was needed on 73mm shells, 3 on 68mm ones.

I 'may' have a spare one, need the check though.

I don't think I understand. If I get a 118mm in place of the 116mm I could get a 68mm version to work?

They are a little different from Shimano's other MTB bottom brackets in that they come with a set of spacers, so that it may be used with either a 68mm or 73mm bottom bracket shell.

Like Ian said, you need one spacer with your 73mm Shell, which I can see in the picture on your first post.



The axle length required will be determined by the Crank that you use.

Pip

 

[Pipmeister]

Re: Re:

I don't think I understand. If I get a 118mm in place of the 116mm I could get a 68mm version to work?

Giving this some thought, as I have..... with respect, I think I'm correct in saying that I (we) don't understand what you don't understand.

When the Shimano 105 was discussed earlier on in the thread with a link to both e-Bay and Chain Reaction, it hadn't been established that your frame has a 73mm shell.

As mechanicalvandal has since highlighted, the 68mm road version (105) will not work in your 73mm Shell, regardless of the axle length.

Does that help explain it?

Pip

 

[Madmax1993]

Re:

The OP seems to be confusing the shell width and axle length. They are separate parameters, and both need to be right. The 68mm or 73mm measurement refers to the width of the BB shell. Measure your frame with a steel rule or Vernier caliper to get this measurement. The second measurement is the length of the axle, and it is completely independent of the shell width. The axle length determines how far the chain set sits from the frame. Both measurements need to be correctly matched to a new BB.
If you get a 73mm BB when you need a 68mm, you won't be able to tighten it flush against the frame, and if you get a 68mm BB when your frame is 73mm, the cups won't fully support the BB when they're tight in the frame.
With axle lengths, if it's too short, your chainrings will catch on the frame, if it's too long, your derailleur might not reach far enough to shift into the big chainring. Too long or too short axles can also throw out your chain line.

As for the spacers sitting between the frame and the BB, if it's anything like the newer hollowtech II spacers, they make a BB shell that is long enough for a 73mm frame running with an E-type derailleur. So if you use a BB mounted derailleur on a 73mm frame, you use no spacers. If you use a band on derailleur on a 73mm frame, you use one spacer (on the driveside). If you use an E-type derailleur on a 68mm shell, you use two spacers (both on the non driveside), and if you use a band on derailleur with a 68mm BB shell frame, then you use all three spacers (two non-driveside, one driveside, IIRC).

 

[Madmax1993]

Re: Re:

The xtr version was designed to work with 68 or 73mm bb shells, with spacers taking up the gap. Iirc, one spacer was needed on 73mm shells, 3 on 68mm ones.

I 'may' have a spare one, need the check though.

I don't think I understand. If I get a 118mm in place of the 116mm I could get a 68mm version to work?

No, you can't use a 68mm BB on your frame if it is 73mm, regardless of the axle length. As mentioned already, if you have a 68mm frame, you can use certain 73mm BBs, with frame spacers, but not the other way around.