Bottom bracket, crank advice

[Naboos shoes]

The BB width frame measurement on my bike frame is 68mm, it currently has a powerspline BB in it that was replaced fairly recently but think it’s on its way out again.
Looking at my options it seems I’m very limited in crank arms etc for this BB. (I run a 34t single chain ring 104 bcd)

Any advice on affordable fair crank setups? Can an external bearing BB be fitted, will it throw my chain line right off?
Anybody selling anything suitable?
Cheers

 

[ishaw]

Re:

An external bb won't harm your chain line at all, all it will mean is you need a compatible crank. The external bb also caters for use on both 68 or 73mm bb shell widths by using spacers (generally 2 on one side, 1 on the other for a 68mm bb shell).

Are you looking for triple, double or single ring?

I've a few spares so might be able to help depending on what you need and budget.

 

[Naboos shoes]

Re:

Sorry for the stupid questions, is my understanding right that for a 68 and 73 shell width you would use the same BB but would use spacers if you had 68mm shell?
Also say for example I was using a hollow tech BB, would the crank used with it be hollow tech specific, or could you use other cranks with a thru axle, ie is there a generic axle diameter/length used with thru axle type cranks giving you more compatibility options?
I’m just running a single narrow wide chain ring 104bcd up front at the moment and happy with it, the bike is07/08 ish so not after anything particularly flashy or vintage but an upgrade on the tatty crank I have at the moment would be good.
Cheers for your help

 

[greencat]

I think I'll add one thing - and then sit back and learn.

Your bike's bottom bracket shell may, I stress may , need facing. Alignment is more critical in external BBs. If you find you are wearing out external BBs quickly, the shell may need facing. I have never had it done, although I can think of one frame of mine that might benefit from it.

I like the external BB system on the whole. It makes taking cranks and bottom brackets off/on very easy. It feels like a similar breakthrough to the aheadset. Even though I've been replacing the older style cranksets for years, I still very occasionally cross thread one or have a left hand one come loose and eventually wear out (I'm talking one of each in the last two decades). The one downside in recent BB innovation - the lack of standards. Some just seems like patent avoidance rather than adding real value.

 

[Naboos shoes]

Re:

Ah, the refacing makes sense with the external cups. I just like the idea of a thru style crank over the traditional BBs, although I know of people using square taper etc for years and no issues.
Cheers, I’ll look into my options

 

[ishaw]

Re:

Not all thru axle cranks are compatible with each other. For example. Most are 24mm straight axles (dianeter). Gxp style cranks have one side of the axle at 24mm the other at 22, so you either need a gxp bb or an adapter to run in a standard ht2 bb.

Other complications are 30mm axles, not bb 30 which require a bb30 bb to work. Other options are bb386 evo, which are again specific to cranks/bb but are 30mm crank diameter and external bb. Other 30mm options are hope and ethirteen, fsa too I think. Probably others.

Basically ht2 (shimano style) will give you most flexibility/compatibility. A 68mm bb will require 3 spacers, a 73mm bb 1. Cranks that fit standard ht2 are many and varied, not just shimano either, race face, FSA are a couple. Just avoid gxp cranks unless you use a spacer.

 

[Naboos shoes]

Re:

Nice one cheers, I see it does get a little confusing. Basically I think I’m going to look for a hollow tech 2 BB and a single chain ring crank and go from there.
Any reasonable BBS You would suggest ? Think I’ve read deore ht2 is pretty good and reasonably priced

 

[ishaw]

Re:

Shimano ones are good, haven't really worked out what the difference really is between say a deore vs xt/r. You may save a but of weight, but minimal.

FSA tend to be a bit poo, don't last that long.

Hope ones are good, have a couple on bikes and can change out the bearings when they wear out. Technically you can do this on all, but hope are designed to be serviceable, others aren't so much but easy enough to tap out bearings and replace.

 

[Naboos shoes]

Re:

Cheers, seen deore BBs for about £20 so worth a punt, then I’ll try find used crank to match. Having never fitted a External BB myself, looking at the cranks, it looks like the bolts at end of shaft set the preload then you tighten the pinch bolts like a headset/ stem ? Would this be correct ?

 

[mattr]

Yes, exactly correct.
End cap is ~5Nm (i think it's printed on) and pinch bolts are 15Nm ish (again, printed on the crank)
(mine are downstairs and i can't be bothered to go look )