cyclopath256

Hi!

I bought a gravel bike a month ago (Cannondale Topstone 1) and I have recently swapped the stem for a slightly shorter one. Now I can hear rattling noise coming from the headset when I ride over stones or potholes. I have tried to fix it several times by loosening the stem screws, tightening the top headset screw slightly (I've heard that one should stop applying force on the screw once it gives back a little bit of resistance) and tightening the stem screws to their correct torque again (5 Nm). It helped in the first 20km, but afterwards the rattling slowly returned. I've tried this procedure a few times and it's clearly not working.

When I apply front brakes and pressure on the front wheel, nothing on the handlebar is moving and everything looks stable. BTW, I applied threadlocker on the stem screws, so they really shouldn't be moving.

Sorry, I took a picture for clarification, but this forum doesn't let me post it, because I am new.

I believe that the headset is somehow slowly becoming loose. What do you suspect? Thanks!

ClydeClydeson

Make sure the steerer tube (top part of the fork onto which the stem is clamped) is a few mm below the top edge of the stem, otherwise you are not pushing the stem down onto the headset. If the steerer is level with or higher than the edge of the stem, you can add a spacer under the stem to bring it up a bit so the top cap is pushing on the stem and not the steerer. If the steerer is significantly higher than the edge of the stem, you can add a spacer on top of the stem to accomplish the same thing.

cyclopath256

Sorry, I am quite new to bike mechanics. I've read your reply many times, but I still somehow don't know what you mean. I've got a spacer at the top, they told me in the bike shop that it needs to be there. I have managed to upload a photo of my headset elsewhere, so you can look at it. This forum doesn't even let me post URLs, so you have to insert it into your browser yourself: ibb.co/NChXZBq

Many thanks!

alcjphil

Remove the top cap and observe how close the steer tube comes to the top edge of the spacer. If it is almost flush you will not be able to preload the headset bearing. This could easily happen if your new stem is smaller in thickness than the old one was. If that is the case you may have to add a very thin spacer to make up the difference

ClydeClydeson

Here is a diagram of the stem and top of headset assembly. The preload bolt needs to pull the top cap such that the stem pushes down on the top of the headset, preloading the bearings. In my diagram you can see that the top of the steerer is up higher that the stem, so when the bolt is tightened the cap is not pressing on the stem but on the top of the steerer, so the stem is not being pushed down onto the headset.

This is an illustration of the one possible cause that I described above. There are other possibilities but if you changed stems and can't get your bearings to preload properly then there is a chance that your new stem isn't as tall as the old one so the steerer sticks out a bit higher than it did before.

cyclopath256

Thanks a lot, ClydeClydeson and alcjphil! I have just compared the original stem with the new one and it turns out that the new one is indeed about 2.5mm smaller! It didn't occur to me to check the height at all! See photo: ibb.co/XJnmg29

Now I understand why it's been rattling, thank you for your contributions! Do I understand it correctly that I need to insert a thin spacer under the stem?

And now on a more serious note: my bike is made of aluminium, but the fork is carbon. I have unfortunately been dumb enough to ride about 150 km/90 miles with this (rattling) setup: ibb.co/9Vp7nbT

Do you think that my lovely new carbon fork could have been damaged?

ClydeClydeson

You could put a spacer above the stem, but there needs to be some steerer tube exposed to hold the spacer in place. It sounds like your steerer is only a wee bit too long so you probably won't have room above the stem and must put the spacer below.

alcjphil

The OP already has a spacer above the stem. Another spacer would probably be better added below it

cyclopath256

Thank you very much to both of you! I have learnt something new today! The carbon fork will hopefully be all right...

Rolla

If the steering tube was really getting slammed around, you might pull the fork and inspect it, but unless your stem was really loose, it was probably just rattling against the headset a bit when you hit bumps. I'd be more concerned about damage from overtightening the compression and/or stem bolts; your torque wrench is your friend.

Freerojo

Yes, you need to make sure when looking at the stem and steerer that the stem is taller by a couple of mm.

Iride01 

Bearings and races are pretty hard surfaces. Have you ever tried to hit a ball bearing with a hammer? The hammer will likely be the thing with the dent in it.

I'd think any damage will be mostly cosmetic if there is any.