Installing a new bottom bracket (BB-UN300, cartridge style)

[Arcturus]

I just installed this BB but it doesn't seem to turn smoothly. On the old style I could adjust the cone so it doesn't press on the ball bearings as much. With this style I can only screw it less into the frame afaik. Any advice?

 

[BikeGremlin]

I just installed this BB but it doesn't seem to turn smoothly. On the old style I could adjust the cone so it doesn't press on the ball bearings as much. With this style I can only screw it less into the frame afaik. Any advice?

BB should turn smoothly, but not very easily. In other words: it should feel buttery (no binding or scratching), but it should take some torque to turn it. If it turns too easily, that means it hasn't got enough preload, and once you step on it, it will create play due to elastic deformation.

So, to confirm that there really is a problem: is the BB binding or scratching?
And, if it is, what is the model?

Relja

 

[Arcturus]

The chain is off and when I spin the crank arms they turn smoothly, I don't hear any noise, but they do stop after 4 turns. I t feels as though something is slowing them down. The model of the BB is Shimano BB-UN300, 68mm - 123mm.

 

[BikeGremlin]

The chain is off and when I spin the crank arms they turn smoothly, I don't hear any noise, but they do stop after 4 turns. I t feels as though something is slowing them down. The model of the BB is Shimano BB-UN300, 68mm - 123mm.

That might be normal (especially if cranks are light and without any pedals). You could remove cranks and spin the axle by hand - that should enable you to feel if there is any binding or scratching, or if it just spins with more preload.

This video shows the quick-check (for Hollowtech II, but the principle is the same for square taper):

The BB in that video is already ridden, but not too much - so that is as smooth as it gets (more than four turns, but the pedals are attached which creates some more inertia).

 

[Arcturus]

I removed the cranks and tried to turn the axle. It spins smoothly, no bumpiness and no noise but with resistance. I will take it this is how it should be. Thank you, I would be wondering if there is something wrong with it!

Since we are on the subject of cartridge bottom brackets, is there a way to clean them? Is it possible to take them apart just to remove grit that got into them? I am not talking about the bearings themself, but the part which screws into the BB shell.

 

[BikeGremlin]

I removed the cranks and tried to turn the axle. It spins smoothly, no bumpiness and no noise but with resistance. I will take it this is how it should be. Thank you, I would be wondering if there is something wrong with it!

Since we are on the subject of cartridge bottom brackets, is there a way to clean them? Is it possible to take them apart just to remove grit that got into them? I am not talking about the bearings themself, but the part which screws into the BB shell.

If the threads are all clean (and you apply some anti-seize paste on the threads and the square taper axle), there is no need to touch anything until the cranks develop play - at least with all the Shimano BBs I've worked with.

You can clean the parts that are visible from the outside, using rags and spunges, of course (just avoid spraying water under pressure to not push dirt inside the bearings). Removing cranks to do the cleaning is pointless, especially since there is always some scratching during the installation (even when you apply anti-seize or grease), so it will just increase wear (if you do it on a weekly or even "only" monthly basis).

 

[Arcturus]

If the threads are all clean (and you apply some anti-seize paste on the threads and the square taper axle), there is no need to touch anything until the cranks develop play - at least with all the Shimano BBs I've worked with.

You can clean the parts that are visible from the outside, using rags and spunges, of course (just avoid spraying water under pressure to not push dirt inside the bearings). Removing cranks to do the cleaning is pointless, especially since there is always some scratching during the installation (even when you apply anti-seize or grease), so it will just increase wear (if you do it on a weekly or even "only" monthly basis).

Prvo cestitke na pobijedi u vaterpolu i zlatnoj medalji, zasluzeno osvojeno!

I ofc don't remove the cranks to wash my bike, but on my last ride something started creaking. I read a bit and BB was one of the reasons it might start creaking. So I decided to remove it and check it out. I didn't even know what kind I had before removing it.

Before removing it, the axle spun smoothly and without any noise, but after reinstalling it I noticed a lot of grittiness when I tried to spin it. It seems as though dirt got in between one of the bearing ring and the part which screws into the BB shell. I tried to clean it, but without removing it I am not sure if this is at all possible.

 

[BikeGremlin]

Prvo cestitke na pobijedi u vaterpolu i zlatnoj medalji, zasluzeno osvojeno!

Hvala. Samo neka bude što više takvih finala - i u fudbalu i u košarci!

I ofc don't remove the cranks to wash my bike, but on my last ride something started creaking. I read a bit and BB was one of the reasons it might start creaking. So I decided to remove it and check it out. I didn't even know what kind I had before removing it.

Before removing it, the axle spun smoothly and without any noise, but after reinstalling it I noticed a lot of grittiness when I tried to spin it. It seems as though dirt got in between one of the bearing ring and the part which screws into the BB shell. I tried to clean it, but without removing it I am not sure if this is at all possible.

For square taper (and Octalink and similar 3-piece crank systems):

When the BB is not installed, you can't really tell if it's OK. Only once it is installed (but before the cranks are mounted) and tightened can you see if there will be any play or roughness in use.

So, if it feels rough when installed and tightened, maybe the bearings are toast (or have a lot of dirt inside and will soon become toast).

 

[Arcturus]

Hvala. Samo neka bude što više takvih finala - i u fudbalu i u košarci!



For square taper (and Octalink and similar 3-piece crank systems):

When the BB is not installed, you can't really tell if it's OK. Only once it is installed (but before the cranks are mounted) and tightened can you see if there will be any play or roughness in use.

So, if it feels rough when installed and tightened, maybe the bearings are toast (or have a lot of dirt inside and will soon become toast).

To english speaking people the following has nothing to do with bike repairs so ignore it.

Tako mi je zao sto niste amere poslali doma u kosarci, nisam mogao vjerovati!