Bottom bracket made of cheese! Help :(

[Lee]

Hoping someone can give us some advice.

Bottom bracket is basically creak crackered, after riding for literally an hour the crank is nearly ready to fall off, starts off creaking then begins to go loose and starts wobbling

Options please? fix or new alternative needed.

Bike is a Boardman pro 29er 2016 model





Thanks.

 

[ChrisEyles]

Stupid question, but are the crank bolts holding the crank to the BB spindle nice and tight? This could be the cause unless the BB unit is actually loose in the frame.

 

[Lee]

Stupid question, but are the crank bolts holding the crank to the BB spindle nice and tight? This could be the cause unless the BB unit is actually loose in the frame.

Hi ChrisEyles, thanks for the reply.

Everything else seems tight, it basically works itself loose on the crankside - I've tightened the 8mm nut up but it works itself loose, tried a dab of locktite so will see tomorrow but don't think it will cure it.

 

[ChrisEyles]

If the crank works itself loose off the BB spindle even after you've tightened up the crank bolts good and hard, I'd have thought that means the crank has deformed slightly where it interfaces with the BB (probably from having been ridden with loose crank bolts at some point). If that's the case it's new crank time.

Just to check and eliminate another possible cause for wobbly cranks, is the BB unit completely secure in the frame?

If you're replacing the crankset, personally I'd swap the BB out for a square taper unit at the same time (Shimano un55 is a sound choice). Avoid replacing with external bearings (hollowtech) unless you know the BB shell has been accurately faced to allow this (which it might not be of it's an older frame).

If you do this you'll need to make sure the BB spindle length you buy is compatible with the cranks you buy. I've slipped up here a couple of times and have had to buy a longer/shorter spindle to get the chain line right.

 

[Grant Fondo]

Why does this happen? Had similar problem with Boardman MTB, just cut my losses and binned the bloody thing. On the flipside, my 25 year old Cannondale has never been touched and BB is still smooth? Luck or just more 'sorted'?

 

[Lee]

If the crank works itself loose off the BB spindle even after you've tightened up the crank bolts good and hard, I'd have thought that means the crank has deformed slightly where it interfaces with the BB (probably from having been ridden with loose crank bolts at some point). If that's the case it's new crank time.

Just to check and eliminate another possible cause for wobbly cranks, is the BB unit completely secure in the frame?

If you're replacing the crankset, personally I'd swap the BB out for a square taper unit at the same time (Shimano un55 is a sound choice). Avoid replacing with external bearings (hollowtech) unless you know the BB shell has been accurately faced to allow this (which it might not be of it's an older frame).

If you do this you'll need to make sure the BB spindle length you buy is compatible with the cranks you buy. I've slipped up here a couple of times and have had to buy a longer/shorter spindle to get the chain line right.

Thanks again, very good post.

I think you could be right here

If I was to get the Shimano un55 could I reuse my original crank arms? ir is it a case of new ones there aswell?

 

[faster]

Thanks again, very good post.

I think you could be right here

If I was to get the Shimano un55 could I reuse my original crank arms? ir is it a case of new ones there aswell?

That's a press fit bottom bracket of some kind, so I doubt there will be any easy or cheap way to fit either a square taper or a hollowtech bottom bracket.

If the only problem you've had is this (no creaking etc), your best bet is probably to replace like with like.

I don't think you'll be able to reuse the crank arms - by the looks of it, the left crank arm and the spindle may well be in one piece anyway. If you try tapping on the end of that axle, the whole thing will probably slide out. I think on these the spindle is aluminium too, so that is probably knackered too if it keeps getting loose.

I think you'll need a full crankset of some type with a 30mm spindle, but I'm sure someone who knows these things better than me will be along soon to advise.

 

[Ajax Bay]

Press Fit BB - in writing in the OP image! UN-55 or Hollowtech II will not fit. Surely the spindle is attached to the right hand spider/crank and can be knocked out (rubber mallet). I surmise that the BB is fine but the crankset is not. Think replacement with a crankset to fit into a PF30 is the best bet, and swap over the chainrings.

 

[Bonefish Blues]

Isn't this what OP needs to fit a square taper BB - but then it's new chainset time and so on...

https://www.wiggle.co.uk/fsa-bb30-c...h5QUe9E9T2l5u2M5qQedtWkfIjwooVMxoCOd0QAvD_BwE

 

[ChrisEyles]

Thanks again, very good post.

I think you could be right here

If I was to get the Shimano un55 could I reuse my original crank arms? ir is it a case of new ones there aswell?

Apologies for my careless reading, didn't catch this was a press fit BB (I have no experience of these I'm afraid).

In that case if the BB is sound, follow @Ajax Bay's advice above and get a new crank that will fit onto the BB spindle you already have.

Square taper/Isis/hollowtech are all different ways of interfacing the crank arms to the spindle, you can't mix and match.

Not come across PF30 on the bikes I've worked on but I'm guessing that's yet another "standard"!

Almost enough to make you want to go back to cotter pins...

 

[CXRAndy]

When you have it all together, is there any play in the crank arm?

If there is, then it would be likely the crank is damaged and needs replacing.

looking at the photo the thread on the inside of the crank looks quite greasy. This will need degreasing before attempting thread locker

 

[Lee]

Brilliant lads thanks for the help.

Yes I believe it is a PF30 BB going off the info stamped on the BB and I have read they are a pain when they go wrong.

I was rather hoping to keep my sram chainset but if I have to change that aswell so be it.

 

[Lee]

Isn't this what OP needs to fit a square taper BB - but then it's new chainset time and so on...

https://www.wiggle.co.uk/fsa-bb30-c...h5QUe9E9T2l5u2M5qQedtWkfIjwooVMxoCOd0QAvD_BwE

Hmm, so If I got that I could then run the Shimano UN-55 BUT I'd have to change my chainset crank? have I got that right??

It's so confusing this BB lark

 

[Lee]

When you have it all together, is there any play in the crank arm?

If there is, then it would be likely the crank is damaged and needs replacing.

looking at the photo the thread on the inside of the crank looks quite greasy. This will need degreasing before attempting thread locker

No play at all, only when riding after say an hour does it start to creak then work loose.

 

[Bonefish Blues]

Yes, that's my understanding