Pedal/Crank Wobble

[roar349]

After some time debating on purchasing a new bike I've decided to hold off for a while and just repair the one I have...

I've changed all the gear/brake cables, still need to replace the brake pads and one of the grip shifts isn't great but usable.

The main problem I have now is the pedalling action isn't 'smooth', there's a big wobble (enough to make the chain slip to the middle cog at the front). So any suggestions? On reading around it sounds as if it may be the bottom bracket, but not sure what size etc I'd need? It's just a cheapo MTB from the local Action Bike's shop (Spitfire made by Lincoln...), bought about 5 years ago, if that helps...

 

[gbb]

You've probably got the basic bearings and coned axle in there roar...personally, i'd take it to your LBS and have a sealed BB fitted. They'll tell you which one you need, and they're not very expensive.

Its not a difficult job to do yourself, but you'll need a BB tool, crank extractor and some tools to get the old BB off.

 

[roar349]

Thanks, I'll pop it along and see what they say.

 

[roar349]

Trying not to swear...

Grabbed a toolkit to look at what bottom bracket size I'd need and didn't find what I'd expected...

Drive side:

Other side:

No idea how to get these off, and even if I do I don't think it's going to have any markings on it to suggest what size it is. This started as a project to stop me shelling out on a new bike and learn a bit, it now looks like I'll have to bite the bullet and take it to the LBS or Halfords to get the thing off...

 

[Alf]

From the photos, it certainly looks like a coned axle with screw-in cups. No sign of a lock ring, though and the one you have indicated as the left side (without the chainrings) is more normally the type you would get on the drive side. Any way, you need a spanner that will fit over the two flats. You might manage with a very large adjustable on the second of the two above but there is a tool that would make the job easier - probably not worth forking out for because you will be unlikely to use it again. If you do try to take it off yourself, remember the one on the right hand side (drive side) will almost certainly be a left-hand thread - ie you turn it clockwise to undo it.

If you take it to a bike shop, it will take them about 30 seconds and with luck they might not charge if you are buying a replacement BB from them.

Good luck
Alf

 

[roar349]

Managed to get the adjustable side off (it was as you said on the non drive side, too much time looking at it upside down), was a tad mucky in there and the bearing cases had disintergrated almost completely.

The fixed cup is a whole nother story, won't budge no matter what. Going to try the sheldon brown method as a last resort before handing it over to a pro...

 

[Crankarm]

Make sure before the new BB goes in the threads are clean and freshly greased. Can't see why you don't give it to your LBS to do as you will probably have to take it to them to find out what size sealed BB to replace it with? Refitting is a 2 minute job.

 

[nuovo_record]

and make sure that you are unscrewng the fixed cup the right way..

 

[SimonR]

Yeah - I did exactly this job last week!

The adjustable side (top picture) should have a lock ring around it to keep it in place - it's missing in your picture.

You don't need to get the other side out to reassemble the bottom bracket - just reach in with a bit of rag and clean it out.

If you do want to remove it you'll need either the correct tool or a set of stilsons to unscrew it CLOCKWISE as it's an opposite thread. It's a pig of a job without the proper tool but much less so if you unscrew it the right way ;-)

To reassemble, buy new bearings (and a new axle if needed - can you feel wear or is it just shiny where the two bearings were?), stick a liberal amount of grease in the fixed cone and put a greased bearing on the axle before inserting it in from the adjustable end...

Easy job but play around with tightness to make sure you eliminate play without getting the bearing too tight.

Have Fun!