Shimano BB/Shell Problem.

[Ray Young]

On my recent Borders ride I thought the Shimano external bb bearings were worn on the drive side as it had developed some play. I have now got around to fitting new bearings. Problem is that on removing the drive side bearing cup I have found that all the thread on it has stripped which is what has caused the play, not the bearings which seem to be OK. Looking back on my last bb replacement I seem to recall that it was a similar problem that lead me to having to replace them then. After that incident I followed the advice of folk on here and had the bb shell cut and chased. What is the likely cause of this? Is the thread on my bb shell worn on the drive side causing the bearing cup to move? If so can it be repaired?

[Trail-rat]

got any spacers in there ?

are they plastic?

plastic spacers cause loosening issues.

ive seen this a few times.

[Ray Young]

Spacers yes, and they're plastic.

[Trail-rat]

yep the plastic spacers squash as you pedal and cause tension loss meaning the bb can unscrew then basically wear the threads as you pedal.

FWIW the lads at goldtec/betd can machine and sleeve your bb and do a very clean factory looking finish.

[Bearbonesnorm]

If the threads in the BB shell are okay and the threads on the BB good when installed then the only cause must be movement between the two in use.

Aluminium spacers would be a good bet, as would a small amount of low strength locktite such as threadlocker.

[Ray Young]

Can you get metal spacers?
What's the chance of my bb shell being damaged? It looks OK and the threads feel to be of equal height when I run a finger over them. All seemed OK on the last rebuild Stu.

[Bearbonesnorm]

Can you get metal spacers?

I'm sure my old FSA cranks / BB came with aluminium spacers.

Difficult to know about the frame Ray but if a BB screws in and tightens up, then I'd suggest the threads are fine.

[Zippy]

Can you get metal spacers?
What's the chance of my bb shell being damaged? It looks OK and the threads feel to be of equal height when I run a finger over them. All seemed OK on the last rebuild Stu.

Yes, in fact IIRC freehub spacers are the same diameter as BB spacers...

If I was in your position, I'd do what Stu said:

Aluminium spacers would be a good bet, as would a small amount of low strength locktite such as threadlocker.

Do it all up, and see how it goes. Have you got a torque wrench to do up the BB cups at a reasonably recommended torque?

I've only ever had the opposite problem of struggling to get them out and have had to jump on breaker bars before!

066 (07-03-2015) by Chris Reeves, on Flickr

[Ray Young]

Can you get metal spacers?

I'm sure my old FSA cranks / BB came with aluminium spacers.

Difficult to know about the frame Ray but if a BB screws in and tightens up, then I'd suggest the threads are fine.

The fit feels quite loose for the first few turns then tightens up. It's a steel frame so I'm assuming the bb cup would wear more easily than the frame, very possibly wrong though. I'll try and get some alloy spacers and see how it goes. No torque wrench but I'll see if I can get hold of one. Thanks for the advice guys.

[Bearbonesnorm]

Go with the Locktite too Ray, as that'll prevent any further movement.

[Ray Young]

Go with the Locktite too Ray, as that'll prevent any further movement.

OK, thanks.

[wfbroddy]

you can pick up torque wrench quite cheap these days, and its going to be accurate enough for your purposes.