Replacement bottom bracket options... confused.

[mrmacmusic]

There's no play in the bottom bracket on my Boardman Hybrid Comp after ~3,400 miles, but it is creaking, and doesn't turn smoothly. I've removed it, cleaned/greased the threads and re-fitted which reduced the creaking for a while, but obviously hasn't done anything to eliminate the roughness. So, I reckon it needs replaced, however I'm wondering if upgrading would be a good idea?

The original bottom bracket on the Boardman (FSA Power Drive) doesn't seem to be that widely available and seems quite expensive at £35 compared to other options. I do have an octalink BB and Shimano 105 triple chainset that I bought in the January sales thinking I'd have the parts to upgrade the drivetrain when the time came, however I'm not sure that I want to convert the Boardman to a triple after all and may just sell these on.

So, will any 68mm x 118mm BB (i.e. square taper, splined) be OK, or could I fit external BB cups like these Shimano 4600 ones and put a 2-piece chainset on (e.g. Sora 3500)..? Would one particular option be more resilient for year-round, all-weather commuting 28 miles a day..?

 

[mrmacmusic]

Anyone?

 

[RecordAceFromNew]

Anyone?

Indeed the Powerdrive is proprietary and now more or less obsolete. For year round all weather trouble-free commuting I think the rational choice is a chainset that: i) has JIS square taper that allows you to get a proven, matching Shimano UN54/UN55 bb, and ii) can take readily replaceable chainrings that don't cost you an arm and leg (or alternatively at such a price that replacing the chainset is no more costly than replacing the rings). To avoid letting the tail wagging the dog, you need to first pick the chainset based on budget/requirement whatever they are, and that will drive your spindle length selection. (UN55 are around £15 a piece new on ebay).

Powerdrive, Hollowtech 2, Square taper, ISIS, octalink etc. are not cross compatible. Most of them also have different spindle length choices which must match the specific chainset to deliver the correct chainline.

Don't know if aesthetic / style matching is important to you, but e.g. Spa's Stronglight Impact/XD2 are highly customisable and aren't particularly expensive. Since Shimano has moved on to outboard BBs i.e. Hollowtech 2 (which imho are intrinsically less durable than the UN54/5, although probably a tiny bit better than Octalink/ISIS), I think you can only get their square tapered chainsets in the lower groups, such as this. Although that is supposed to be 8 speed, since 8 and 9 speed chains have exactly the same inner width, I can't see why it won't work perfectly with a 9 speed chain (assuming you have 9 speed).

Hope it helps.

 

[andrew_s]

The frame will determine that you use a 68mm BB if it's a cartridge type (Taper or Isis/Octalink). The length is determined by the crankset used, and is generally recommended when you buy the chainset..
I'd recommend a Stronglight Impact or XD2 chainset with a 110mm UN54 or 55 BB (or 107mm for double) for long life and reliability.
The BB is good for being ignored for several years (20-25,000 miles). The only thing is to make sure there is copaslip or similar anti-seize on the threads so you can get it out when it does eventually die. Death is usually non-urgent, in that a couple of months after you first notice play in the cranks won't hurt.
The XD2 is a solid crank, which I've never managed to break, unlike Shimano, TA or Middleburn. The cheapest option is this XD2 triple for £35. Older Impact are actually also XD2 (it's a Sugino model), but there's also a new version without one of the bolt holes hidden behind the crank arm for a bit more. This newer version needs a slightly longer (~5mm) BB.

 

[mrmacmusic]

Thanks RAFN and Andrew_S

I hadn't come across the Stronglight/XD2 cranks, but while aesthetics aren't overly important I did like the idea of upgrading to a matched Shimano groupset. Despite having the octalink BB (68x118) and Shimano 105 triple chainset/front derailleur on the shelf ready to fit, I think I've pretty much decided I don't want to change to triple, and quite like the idea of a Sora 3500 double.

I understand that cartridge bottom brackets have different spindle lengths, but how do 2-piece cranks (like the Sora) work, and would one fit the Boardman..?

 

[Mile195]

My BMC came with Shimano Hollowtech cups and Shimano 105 double chainset and cranks.

http://www.evanscycles.com/products/shimano/105-5700-bottom-bracket-cups-ec023146.

They simply screw in, one on each side (I'd put some lithium grease on the threads though). The plastic insert you put in with one side, then screw on the other. Knock the crank through with a few taps from a rubber mallet.

I just changed mine. They had done nearly 13'000 miles, all year round in all weathers if that's any help. There was play in them by the time I changed them, but they hadn't failed spectacularly or anything. Probably would have got a bit more out of them if I'd wanted.

My BMC uses a british thread. On a Boardman, I'd be very very surprised indeed if yours didn't.

 

[mrmacmusic]

My BMC came with Shimano Hollowtech cups and Shimano 105 double chainset and cranks. They simply screw in, one on each side (I'd put some lithium grease on the threads though). The plastic insert you put in with one side, then screw on the other. Knock the crank through with a few taps from a rubber mallet.

They had done nearly 13'000 miles, all year round in all weathers if that's any help...

Cheers

So, I don't need to worry about the width of these 2-piece cranks then (in the way that I'd need to get the right spindle length on a cartridge-style bottom bracket)? Just grease the threads, screw 'em in and then (gently) tap the crank through... sounds ideal, and I'd be more than happy with a >10k mile all year all weather lifespan.

 

[Mile195]

Well the plastic insert is still a specific length. You could leave it out, but it wouldn't do the axle much good as it would be exposed to any water and grit that gets into the frame.

I imagine it will be the right length though - Boardman isn't a particularly exotic make or anything - I imagine most parts will conform to normal standards. I'll measure the width from the inside of the cups on my lunchbreak and get back to you.

 

[mrmacmusic]

Well the plastic insert is still a specific length. You could leave it out, but it wouldn't do the axle much good as it would be exposed to any water and grit that gets into the frame.

Ah, I see... that makes sense now. Thanks again Mile195

 

[Mile195]

I make that 68mm. Obviously if you go for one of these you'll need the crankset to fit. You'll also need the tool to fit them which is readily available:
http://www.evanscycles.com/products/park/bb-and-crankarm-tool-hollowtech-2-ec008302

Don't get the tool from evans though. It's about £7 cheaper everywhere else!

These bearing cups come with the spacer you need for a triple, in case you want to use the one you already bought.

If you want to do it properly, you will need a torque wrench to refit the crank arms, though you could manage without - just be careful not to overtighten the bolts. They round off easily. The Bearing cups also specify a torque, but I wasn't paying out for Shimano's own socket so I could use my torque wrench, so I just did it up until it felt right using the tool above.

Good luck!!

 

[Howard]

All good above - the one gotcha missed out when moving from a frame that was originally spec'd with a cartridge BB to an outboard is to make sure you get your BB shell 'faced' if it hasn't been already.

If you do not get the shell faced the outboard cups will not line up perfectly and you'll go through BB bearings like no tomorrow.

 

[mrmacmusic]

View attachment 28492

I make that 68mm... ...Good luck!!

Thanks again Mile195 – much appreciated

All good above - the one gotcha missed out when moving from a frame that was originally spec'd with a cartridge BB to an outboard is to make sure you get your BB shell 'faced' if it hasn't been already.

If you do not get the shell faced the outboard cups will not line up perfectly and you'll go through BB bearings like no tomorrow.

Hmm... is it possible to tell just by looking if this has been done at the factory or not? Presumably not, as the original spec on the Boardman was a cartridge BB.

'Facing' sounds like it grinds the surfaces flat and ensures both left and right are perfectly parallel (?) – should I be overly concerned on an all-year all-weather commuter that this process will (presumably) remove the paint finish? I supposed the exposed surface would not rust of course, and would be covered by the cups anyway.

 

[Howard]

You can have a look - if there's no paint on the faces and you suspect the paint has been ground off purposefully (look for a dead straight line) - then it might have already been done.

If not drop it in the LBS and have it done. You are correct - a special tool is used to grind the faces flat and parallel. The frame is ali and yes - once bare it will oxidise but luckily ali oxide is more resilient than iron oxide and forms a nice protective layer.

Your other option is to just fit the outboard BB anyway and hope you can get away with it. But if the outboard fails early i.e. < 1000 miles then you can be 99% sure the surfaces are not parallel.

 

[mrmacmusic]

You can have a look - if there's no paint on the faces and you suspect the paint has been ground off purposefully (look for a dead straight line) - then it might have already been done.

If not drop it in the LBS and have it done. You are correct - a special tool is used to grind the faces flat and parallel. The frame is ali and yes - once bare it will oxidise but luckily ali oxide is more resilient than iron oxide and forms a nice protective layer.

Your other option is to just fit the outboard BB anyway and hope you can get away with it. But if the outboard fails early i.e. < 1000 miles then you can be 99% sure the surfaces are not parallel.

Thanks again Howard