This post is more of a note to self, so unless you have a headset clunking noise when going over rough surfaces, there’s nothing to see here – please step away…

A couple of weeks ago I noticed that there was a frustrating rattling or clunking sound coming from the headset area of my Colnago when riding on uneven roads. I had recently changed the handlebar stem so I assumed that maybe the stem wasn’t far enough down on the steerer tube, causing the bearings to be loose. I checked for play in the bearings by rocking the bike back and forth with the front brake applied and feeling for any movement between the top of the fork and the head tube. It seemed that there was a very slight amount of movement detectable, so I loosened the stem bolts and tightened up the pre-tensioner bolt on the top of the stem until I could feel no play, then I tightened the stem bolts to 4Nm using a torque wrench.

On the next ride, I was still experiencing the clunking sound, and yet off the bike it was impossible to recreate it even by bouncing the bike up and down at the front. I started to suspect other things. I checked for loose wheel nuts, loose bottle cage bolts, etc. I even changed the front wheel in case it was due to wheel bearings. But the noise remained.

So I took the whole stem and spacers off to see if there was anything amiss. I didn’t find anything. So I re-assembled the whole lot. This time I tightened the pre-tensioner much further than it had gone before – being careful to always see that the fork was still turning freely. I couldn’t believe that I could still keep tightening it without the fork seizing up. I periodically took the top cap off to check the distance between the top of the steerer tube and the top of the stem (or spacer). The gap was reducing slowly, indicating that I was taking up slack in the bearings.

Then, the top-cap could be tightened no further – I knew what this meant – that the top cap was now coming into contact with the top of the bung in the steerer tube, meaning that there was no more adjustment left. The photo shows that there is only about 1mm between the top of the spacer (outside) and the fork bung inside, and that is not enough clearance for the dished top cap, so the cap was ‘bottoming out’. However, I had tightened it significantly more than I had done previously, so I hoped it would be enough.

The fork was still turning freely at this point so I knew I had not over-tightened it.

I ordered another 3mm spacer just in case I needed to tighten it further in the future.

This morning I went out on this test ride:

The noise had gone, and the bike was back to its smooth Rolls-Royce style feel! I also managed to beat my previous best up Yalding Hill by over 10 seconds. Yay!

Edit (25th May 2014): After the headset started rattling terribly on this ride, I decide to investigate. I removed the handlebar stem completely, and this is what I found: The bung in the steerer tube was not seated fully. It had pulled out by about 6mm. That accounts for a couple of problems I wrote about in the original post above. It explains why the forks didn’t seem to be getting tighter when I was tightening the top-cap – obviously as I was tightening, the bung was gradually being pulled out of the steerer tube, so the stem wasn’t being fully tightened onto the forks. And now it’s obvious why the top-cap ‘bottomed out’ on the bung.

So I loosened the bung and pushed it down fully into the steerer tube. Because the steerer tube is carbon, I wanted to make sure I used the correct torque setting when tightening the bung. I spent at least half an hour searching the internet for this elusive piece of information. When I came to tighten it, I realised that the torque setting is printed on top of the bung – doh! It was 8Nm. So I tightened it to that torque and refitted the handlebar/stem assembly. I tightened the pre-tensioner top-cap down to the correct torque (4Nm), and tightened the stem bolts.

Now there is no rattle. Although the unseated bung explains some of the things described in the original post, it doesn’t account for why the headset became loose when once it was tight. For that to happen the stem must slide up the steerer tube to some extent (maybe that can happen on really rough roads). Either that or the bearings ‘settled in’ somehow.

I recently ordered a pair of Campag Shamal Ultra wheels for my Colnago. When I got home from work last Tuesday they had arrived. I rushed to fit tubes, tyres and cassette to them to go out for a quick test ride before it got dark. According to the advert, the rear was fitted with a Shimano 9/10-speed compatible hub; that meant that I needed to fit a 1 mm spacer behind the cassette. So that’s what I did, but the cassette felt slightly loose. When I went out for my test ride I had to cut it short after just a mile or so because there was a terrible (yet familiar) rattling coming from the cassette every time I rode over a bump in the road. It even slipped a gear as I was returning up Barn Hill. I didn’t have time to investigate it fully for a couple of days, but I did quite a bit of research on the web to no avail; it all confirmed what I already knew – i.e. a 1 mm spacer was all that was required.

When the weekend arrived I decided that I would take the cassette off and measure the length of the hub and compare it to the length of the hub that the cassette originally came from (supposedly the same Shimano 9/10-speed). I took the cassette off and while I was measuring it I noticed the words “11-SPEED” printed on the hub.
Aha! So it wasn’t a 9/10-speed hub – it was 11-speed. I immediately consulted this goldmine of information and saw that I needed a 1.85 mm spacer in addition to the 1 mm I already had. Further research revealed that this spacer should have been supplied with the wheels, so I was a bit peeved that it hadn’t been. Even worse: they didn’t seem that easy to get hold of either; someone on eBay was selling them for £6 each!  I wasn’t going to pay that much, so I called a couple of local bike shops to see if they had any. The first one said no. The second one, after a lengthy discussion, during which I convinced the so-called ‘expert’ that 11-speed hubs were longer than 9/10-speed hubs, said no, but they did have plenty of 1 mm spacers in stock; maybe I could use two of those?

So I decided to ride to the said LBS to get a couple of 1 mm spacers (£1 each). However, I still really wanted to try out my new wheels. But I didn’t have the required 1.85 mm spacer – but I remembered that there was a 1.75 mm spacer on my Mavic wheels; surely that would be close enough! So I proceeded to take the cassette off the Mavics to borrow the 1.75 mm spacer from there. By this time the kitchen table had 3 rear wheels and various cassettes and bike tools all over the place – it looked like a bike workshop! I next refitted the cassette to my new wheels using the borrowed Mavic spacer and the 1 mm spacer. It was fine – totally secure, with no wobble.

I rode to the bike shop (the new wheels felt great) and asked about the spacers. A mechanic emerged from the workshop with 2 spacers in hand and said “there you go”. I said “so they should be the same as this one”, as I pulled from my back pocket a 1 mm spacer that I had taken along for comparison. He took it from me and lined it up next to one of his and said “these are slightly thicker than your one”. “Aha, that could be even more useful”, I said, knowing that I was actually after 1.85 mm, and at the same time thinking “I won’t be bringing my bike here for any work; they don’t even know that a 1 mm spacer should actually measure 1mm!” I bought the spacers and was on my way.

As soon as I got home I measured the new spacers using a micrometer. They were 1.6 mm! After further experimentation, the details of which I won’t go into here, I decided that the 1.6 mm spacer seemed to work fine, as a substitute for the more correct 1.85 mm one.

Anyone who has actually read this post to this point must either be

1. trying to fit a Shimano 10-speed cassette to an 11-speed hub, and finding the information in this post quite useful, or
2. seriously in need of ‘getting a life’!

Either way, here’s a diagram to help explain (notice they specify 1.8 mm, not 1.85):

I now know much more than I ever wanted to about cassette/hub/spacer compatibility! I am also an expert in changing cassettes, having done it about 20 times during the course of this exercise.