Traditional Cup and Cone Bottom Bracket Upgrade with Shimano BB-UN300 bottom bracket British thread; 68 - 122.5 mm (LL123) - for chaincase

[Clemenza]

Hi

I recently upgraded my traditional cup and cone bottom bracket with the appropriately sized BB-UN300 on my Viking Prelude bike. However, after fitting, I was concerned that the cup on the non-drive side was projecting some 8 mm or 9 mm. I initially assumed that this was due to the lack of available threads inside the frame’s bottom bracket shell and decided to have it chased out, which would resolve the issue. Despite the mechanic at Evans Cycles completing the work today, the projection is still there and I have been advised that the cup was being prevented from going deeper into the Frame Shell not because of the lack of threads, but by the actual bearing on the Shimano BB-UN300 itself. I am clearly at a loss as to why this might be so, having meticulously ensured that I was purchasing the correct component, on the basis of the original bottom bracket spindle and the specific size of the bottom bracket shell on my Prelude.

I would be grateful for any advice or suggestions on resolving this issue, although I would once again confirm that, according to all the details I had, the correct Shimano component has been purchased. I attach some images of the bike and both sides of the Bottom Bracket installation for information.

 

[midlife]

Have you got some sort of weird narrow bottom bracket shell ?

 

[Ajax Bay]

Please describe each image. The first ones don't look like a UN-300 to me.
I suggest you amend (edit) the OP, deleting the images and reattaching ones with the new BB in.
The image of the bike is one you posted 4 years ago here.
What is that slotted lockring? One for the cup&cone bearings, no?
Please share the SKU or other identifier for the BB you bought. Are you sure you have a 68 and not a 73?

No idea about the spacer's function.

 

[Clemenza]

It is the same bike that I have had for more than 4 years.
The four images three images were taken today, 2 of the non-drive side and 1 of the drive-side, fully driven home and supporting the chainguard bracket.
SKU: BBUN300KB23. The spacer fits between the BB Flange (Drive Side) and the Chainguard Bracket and is just visible on photo 4.
The lockring comes from the original cup-and-cone BB and is fitted solely to add strength and integrity.

 

[fossyant]

I suspect your BB shell (the frame) is less than 68mm or it's 68mm and you bought a 73mm BB . You'll need to measure it.

Get rid of the lock ring on the non-drive side - that old thing serves no purpose.

You did buy a 68mm shell version and not 73mm ?

 

[fossyant]

Looks like that's a 73mm BB you've bought. There are two sizes, 68mm for road bikes and most hybrids etc, 73mm for mountain bikes. Remove the lot and let us know the numbers on the BB shell (that's inside) or what's on the box.

 

[Ajax Bay]

Thank you.
Does your BB shell measure 68mm?
Extract the BB. When the NDS side is pushed onto the main part, are the faces approx 69mm 'wide'?
If a double 'yes' then aiui you are saying that even with serious torque the NDS side will not screw in further.
The only thing stopping the NDS going in properly is lack of threading depth inside the BB shell on the NDS side (for some reason) but surely the LBS would chase/cut to the necessary depth.
Threading the c&c lockring adds zero to the BB's "strength and integrity" but has helped confuse.
Your driveside image is a thumbnail (for me) and cannot be enlarged to be useful (though probably not needed as the DS side has screwed in).

 

[Clemenza]

Thank you.
Does your BB shell measure 68mm?
Extract the BB. When the NDS side is pushed onto the main part, are the faces approx 69mm 'wide'?
If a double 'yes' then aiui you are saying that even with serious torque the NDS side will not screw in further.
The only thing stopping the NDS going in properly is lack of threading depth inside the BB shell on the NDS side (for some reason) but surely the LBS would chase/cut to the necessary depth.
Threading the c&c lockring adds zero to the BB's "strength and integrity" but has helped confuse.
Your driveside image is a thumbnail (for me) and cannot be enlarged to be useful (though probably not needed as the DS side has screwed in).

Thank you.
Does your BB shell measure 68mm?
Extract the BB. When the NDS side is pushed onto the main part, are the faces approx 69mm 'wide'?
If a double 'yes' then aiui you are saying that even with serious torque the NDS side will not screw in further.
The only thing stopping the NDS going in properly is lack of threading depth inside the BB shell on the NDS side (for some reason) but surely the LBS would chase/cut to the necessary depth.
Threading the c&c lockring adds zero to the BB's "strength and integrity" but has helped confuse.
Your driveside image is a thumbnail (for me) and cannot be enlarged to be useful (though probably not needed as the DS side has screwed in).

Just to be clear, the mechanic from Evans Cycles chased and extended the threads on the NDS cup and actually installed the new Shamino BB-UN300.

Additionally, I have today raised the issue with Madison, who is apparently the agent for Shamino in the UK. I sent the same images as I have posted on here, together with an email explaining the problem. I also sent mock-up image of another Shamino BB-UN300 dry-assembled. In it, I try to illustrate, using a digital Calliper, why I think the NDS cup is projecting. Specifically, because it is too wide for the 68 mm BB shell in the frame.

This is the explanation I received and about which I would invite comments/observations.

I do understand that you have visited an Evan cycles to look into this matter.

However, from the pictures I did attach. It clearly shows that the stock bottom bracket I do have here which is a 68mm bottom bracket. As to your photos is at and around the 74-75mm when assembled outside of the bike. The retain compound I am referring too. Is within the bearing cup. Under correct installation. This will compress and deform to make a secure fit. Therefore, making these bottom brackets a 1 time fit. I do trust that the non-drive side cup is still showing this retaining compound to be in place.

As before I can only advise that you visit a local Shimano service centre who can advise of the correct installation and fit.

Here is the cup which is referenced in Madison's response

 

[Ajax Bay]

Bargain for anyone wanting a ST BB:
https://fawkes-cycles.co.uk/shimano-bb-un300-bottom-bracket-british-thread-bsa-p28234

 

[rogerzilla]

The UN-300 is basically an enshittified square taper BB because Shimano wants you to buy new splined cranks. The cups do look ridiculously long compared to UN-55 cups.

 

[Fastpedaller]

It doesn't look as though the LH cup is going on to the unit (judging by the blue sealer that not been disturbed)
To be sure the LH cup fits into the bb shell, I'd keep the rest of the cartridge 'on the bench' and just screw the LH cup in to see it can fit all the way.
With the photo provided of the assembled unit and the vernier, it appears the parts are faulty, as the measurement is too wide as stated, so it's a bit of a mystery.
I'd usually expect the LH cup to fit on as far as covering the bearing race, and it's several mm short of that - maybe the bore of the LH cup is undersize and preventing it? With this design of BB, it's not unknown to have a concern about loose fit of the LH cup over the bearing!

ETA - I've just looked at the photo again and realised the LH cup has an extended, unthreaded part which I thought was the bearing race in the photo. My comments about the cup not assembling into position still apply.

 

[Fastpedaller]

Any update OP?