Giant Defy 2018 BB replacement

[fraz101]

My drive side BB was rough and noisy on my 2018 defy carbon frame with metal bb insert

I replaced with BB72-41B
The drive side cup pressed in as it should with no issue.

The non drive side pushed in far easier and did not need to press at all, a firm press with my hands inserted it.

I used a smear of grease to insert the new BB

When installing the cranks the non drive side cup pushed out a little and I had to push back in.

I’ve spoken to a bike mechanic friend who assures me it will be absolutely fine but I wanted some other opinions.

You read so much about press fit BB issues that it alarms me a little.

 

[Cycleops]

The fact that the non drive side pushed in very easily highlights the problem with pressfits, poor tolerances in manufacturing. They are the work of the devil.
Proof of the pudding will be in the riding so that's all you can do.

 

[13 rider]

I presume you took the old BB out . How much force did it take to remove the non drive side , was it noticeablely tighter than the one you fitted ?

 

[Ajax Bay]

Your description suggests that the BB shell on the left hand side is out of tolerance (diameter too large) and so the necessary interference fit is not achieved. The 'cup' (and therefore the spindle) will move (rotate and some radial movement) in the shell during the miles and the bearings will wear and fail more quickly than 'normal'. Examination of the spindle may show the sign of this from the previous LH bearing (if it was a bit loose). How many miles do you think you'd done on the last set?
Maybe the last set was installed with retaining compound (OP doesn't mention).
I commend this article: https://www.hambini.com/engineering-analysis-grease-or-retaining-compound/
https://www.hambini.com/bottom-bracket-pressfit-and-creaking-an-engineering-analysis/

 

[Cycleops]

From the score marks in your pic it suggests the bearing has been moving, whether application of retaining compound can stop this remains to be seen. You can only try.

 

[Jameshow]

Would a dab of locktite help? Not sure which one ..?

Or a bearing glue?

 

[fraz101]

I presume you took the old BB out . How much force did it take to remove the non drive side , was it noticeablely tighter than the one you fitted ?

It was fairly tight to remove with a punch. Both sides were of equal tightness to remove

Your description suggests that the BB shell on the left hand side is out of tolerance (diameter too large) and so the necessary interference fit is not achieved. The 'cup' (and therefore the spindle) will move (rotate and some radial movement) in the shell during the miles and the bearings will wear and fail more quickly than 'normal'. Examination of the spindle may show the sign of this from the previous LH bearing (if it was a bit loose). How many miles do you think you'd done on the last set?
Maybe the last set was installed with retaining compound (OP doesn't mention).
I commend this article: https://www.hambini.com/engineering-analysis-grease-or-retaining-compound/
https://www.hambini.com/bottom-bracket-pressfit-and-creaking-an-engineering-analysis/

I think they are the original BB bearings that I removed but I bought the bike 2nd hand. I have covered 6500miles on it

 

[Ajax Bay]

Sounds like the best bet is to get the activator and the retaining compound suggested in the article and use that, on the LH cup.
https://www.glueonline.co.uk/product/loctite-641-10ml/
https://uk.rs-online.com/web/p/adhesive-activators-primers-debonders/3303970
https://www.glueonline.co.uk/product/loctite-sf-7649-150ml/
Beware counterfeits. I am not recommending either of these suppliers.

 

[fraz101]

I see Hambini uses loctite 641

However I’m not too happy to bond it in.

I think I will leave it as is for the moment and keep my eye on it.

I am meticulous in my maintenance of my bikes and I have my cranks off every month or so (more often at this time of the year up here in Scotland)

It’s strange because I had to punch out the old ones,they weren’t too tight to remove but I definitely needed a good few hits to get them out

Here is a photo of removed worn BB