Replacing triban 3 bottom bracket and / or crankset...

[nickAKA]

Morning all,
I picked up a SH triban 3 with 650 wheels for the wife to use on the turbo (and to try to tempt her out on the road with me when the weather improves).
It's like new, itlooks like it's never been outside, but there's a definite wobble on the chain rings which is causing me some irritation due to the chain rubbing the front mech once per rev - very annoying when using indoors!
I suspect it's been dropped and the square 'spindle' through the BB is bent, but it could be the crankset... It's a sora triple with an 8 speed cassette, so I'm seeking advice on replacing both the BB & crankset.
Research suggests the BB is 'square tapered' which is a shimano UN55 68 x 115 (english) I believe?
For the crankset, I will try & track down a new sora triple, but if I can't find one what would my options be? I have my doubts that a used crankset would be any better than the one it would replace
Many thanks in advance!

 

[Tim Hall]

Very unlikely that the BB spindle is bent. There would be other damage to the bike before that happened.

When you say wobble, is it possible to move the crank relative to the frame by pulling on the cranks at 90 degrees to their normal direction of travel.?

 

[raleighnut]

It could be the crank just needs 're-seating' on the taper, I'd try whipping it off and re-fitting as long as @Tim Hall 's post about the BB holds up and there is no play.

 

[Cycleops]

You can rule out a bent spindle. Could be The chainrings are bent or even that the bolts holding them are loose. Take the chain off and move the chainset about and spin it, it should then be apparent what the problem is.
If you do have to replace the chainset Sora has a hollowtech BB which comes with its own outboard bearings, quite a good upgrade In itself.

 

[Ajax Bay]

Plus 1 for first action to reseat the right hand crank on the square taper.

Sora has a hollowtech BB which comes with its own outboard bearings, quite a good upgrade In itself.

In what way is Hollowtech BB an upgrade on a UN55 square taper?

 

[Sharky]

Can you be more specific about the "wobble". Is it on both/all chain rings and is it on the inside or outside ?
Can it be that the front gear cable just needs tightening or loosening, or the high/low stops need adjustment?

 

[bonzobanana]

UN55 is a very decent bottom bracket but if they do fail with regard bearings etc you'd expect to hear a lot of noise to go with or a grinding action as you rotate the crank. Would of thought either crankset or bottom bracket incorrectly fitted or some light damage/bending to the chainring which is not easily visible. You don't mention any noises so bent chainring seems most likely.

 

[Cycleops]

In what way is Hollowtech BB an upgrade on a UN55 square taper?

Ok that’s debatable and many die hards will favour the yonks old square taper because it’s dependable and long lasting. The hollowtech features a two piece crank which you can remove without tools, it’s stiffer and the outboard bearings help. It’s lighter. There’s only one crank length. Not many quality bikes still use square taper. Nearest would be the octalink.

 

[cyberknight]

Ok that’s debatable and many die hards will favour the yonks old square taper because it’s dependable and long lasting. The hollowtech features a two piece crank which you can remove without tools, it’s stiffer and the outboard bearings help. It’s lighter. There’s only one crank length. Not many quality bikes still use square taper. Nearest would be the octalink.

When my hollowtech axle snapped i read actually happens a fair amount compared to square taper , and internal bearings are good if your planning to ride the bike all year in all weathers.
Without seeing the OPs bikes wobble it could be anything , unlikely that the crankset is toast ,If you have play in the crank arms are th bolt that holds it to the BB loose or does the BB wobble in the frame ?

 

[chriscross1966]

Very unlikely that the BB spindle is bent. There would be other damage to the bike before that happened.

When you say wobble, is it possible to move the crank relative to the frame by pulling on the cranks at 90 degrees to their normal direction of travel.?

Echo this, a bent BB spindle is pretty hard to do without savage damage elsewhere, a crank that has come slightly loose then jammed skew is more likely. Ignore Hollowtech2 as an upgrade and see if you can find an old Campagnolo Mirage or Veloce triple on Ultratorque outboard bearings (avoid Powertorque like the plague BTW)..... or check the seating on your crank.... The UN55 bottom bracket is pretty highly regarded as a cartridge square-taper, you have to get into exotica like Phil Woods or a Royce etc before you'll find something on JIS taper that is significantly better

 

[nickAKA]

Thanks for the replies chaps, I'll run through the questions based on observations from memory as I'm in work...

1) All 3 chainwheels are running out equally and in line, probably by a couple of mm in all, just enough to catch the mech. Not wobbling as such, always out at the same point of revolution, poor choice of language on my part that!
2) there is no obvious noise or grumbling coming from the bearings, it all feels pretty smooth
3) couldn't detect any lateral movement in the chainrings but I'll have a proper check of that later
4) the crank arms when pedalling don't have that 'weird see-saw motion' you can always detect when you get on an old wreck
5) no visible signs of damage / impact anywhere...

But the seating of the taper is definitely a good suggestion and worth checking first, may have been assembled badly and I can check it for flatness properly here in work.

 

[Cycleops]

Could be the retaining bolt is loose on the spindle. Hold the end of the crank and wiggle it to feel any movement.

 

[bonzobanana]

Thanks for the replies chaps, I'll run through the questions based on observations from memory as I'm in work...

1) All 3 chainwheels are running out equally and in line, probably by a couple of mm in all, just enough to catch the mech. Not wobbling as such, always out at the same point of revolution, poor choice of language on my part that!
2) there is no obvious noise or grumbling coming from the bearings, it all feels pretty smooth
3) couldn't detect any lateral movement in the chainrings but I'll have a proper check of that later
4) the crank arms when pedalling don't have that 'weird see-saw motion' you can always detect when you get on an old wreck
5) no visible signs of damage / impact anywhere...

But the seating of the taper is definitely a good suggestion and worth checking first, may have been assembled badly and I can check it for flatness properly here in work.

Maybe the cup of the bottom bracket is damaged on the non-drive side or even missing to allow a little bit of movement. Seems unlikely but fits the symptoms. So when driveside pedal is at the bottom the chainrings are a little further out from the frame at the top and when the non-drive side pedal is at the bottom the chainrings are a little closer at the top. Maybe there is a small crack in the frame around the bottom bracket shell somewhere (hopefully a remote possibility).

 

[raleighnut]

Thanks for the replies chaps, I'll run through the questions based on observations from memory as I'm in work...

1) All 3 chainwheels are running out equally and in line, probably by a couple of mm in all, just enough to catch the mech. Not wobbling as such, always out at the same point of revolution, poor choice of language on my part that!
2) there is no obvious noise or grumbling coming from the bearings, it all feels pretty smooth
3) couldn't detect any lateral movement in the chainrings but I'll have a proper check of that later
4) the crank arms when pedalling don't have that 'weird see-saw motion' you can always detect when you get on an old wreck
5) no visible signs of damage / impact anywhere...

But the seating of the taper is definitely a good suggestion and worth checking first, may have been assembled badly and I can check it for flatness properly here in work.

You may find that the crank runs true if you rotate it 90% on the shaft, obviously you'll need to realign the other side but it may run more true.