Carbon paste for steerer tube?

mitchgixer6

Hi all

Having just installed my first full carbon fork I went out for a test ride today. When I got back there was slight movement in the headset. I can only presume this was because I didn't tighten the stem bolts enough. I must admit I was a bit wary of over tightening them due to the lack of a torque wrench.

I re adjusted them tonight and have done the bolts up slightly tighter, but was just wondering if carbon assembly paste should be used at all?

Thanks
Michael

spankwilder

No paste, torque wrench recommended!

JayKosta

I don't understand what parts were loose.

Was it the tightness of the handlebars clamping to the stem?
The stem clamping to the steering tube?
Did the fork have up-down, or side-to-side looseness in the headtube?

When you began to tighten the bolts (which ones?) did they seem looser than when you previously tightened them?

Jay Kosta
Endwell NY USA

mitchgixer6

Thanks guys. I know I need a torque wrench but haven't got round to buying one yet.

There was slight movement in the headset with the brake on rocking the bike back and forth. I can only presume the stem bolts at the steerer weren't quite tight enough. I did also have to tighten up the bung that's inside the steerer too but it couldn't have been this causing the slack in the bearings unless the stem wasn't tight enough.

turnerjohn

make sure you have enough space for the headset to pre-load tight or your just be pulling it onto the spacers etc

Yossie

That movement is headset bearings - nothing to do with sterer bolts (they just hold the steerer on).

Loosen steerer bolts, adjust head set bolt, torque stem bolts back up.

No point waiting to buy a torque wrench - you need one now to do this properly - they are only £20 odd, so not to bad to pick up today and do all this tomorrow over a beer.

maddog 2

stem doesn't need to be super-tight on the steerer anyway. The turning force on the steerer tube isn't that much. Not like a stem/bar interface, which has your bodyweight pushing down on it when you descend bumpy roads.

Yossie

maddog 2 wrote:

stem doesn't need to be super-tight on the steerer anyway. The turning force on the steerer tube isn't that much. Not like a stem/bar interface, which has your bodyweight pushing down on it when you descend bumpy roads.

Exactomondo - 5Nm is tops really for the stem side bolts (all they do is hold the stem in a straight line).

mitchgixer6

Thanks again for all the replies.

The stem actually keeps the set pressure acting on the headset bearings once it's been adjusted via the top cap. In theory once the stem bolts have been tightened on the steerer, the top cap (and bung) could be removed as the only purpose they serve is to pre load the bearings to the correct tightness before nipping up the stem bolts.

My original question regarding the carbon paste was in case this would stop the stem slipping upwards if indeed the stem bolts were slightly too loose. As I said before the stem bolts must have been too loose as this is the only way that the headset would loosen off to a value less then the pressure exerted on them during installation. If the stem was tight enough then even taking the top cap off wouldn't affect the pressuring being exerted on the bearings.

keef66

I had this when I put my Scott CR1-SL together. I think the first ride just settled the components a bit, so I had to loosen the clamp bolts and snug the top cap down a tiny bit more. Been fine since then.

k-dog

mitchgixer6 wrote:

As I said before the stem bolts must have been too loose as this is the only way that the headset would loosen off to a value less then the pressure exerted on them during installation. If the stem was tight enough then even taking the top cap off wouldn't affect the pressuring being exerted on the bearings.

Your second part is right - but it's most likely that your headset wasn't preloaded properly - after a ride everything has now jiggled into place and you need to do it again.

Like has been said already it doesn't take much pressure to hold a stem to a steerer - much less then stopping it rotating with the leverage of the bars.

dodgy

Trek has issued some advice on carbon paste and carbon steerers some time back.

http://thegoldenwrench.blogspot.co.uk/2 ... rding.html

mitchgixer6

Thanks guys, and thanks for the Trek link.

I have a funny feeling that my stem (Zipp Service Course) might actually have been faulty. I had loosened everything off again last night to re align the stem, and when I was re tightening the steerer clamp bolts there was a loud crack long before I got to what I deem to be a sufficient torque.

Took the bolt out and there was a spring like piece of metal wrapped round the bolt. This is obviously the thread from inside of the stem as I cannot tighten the bolt now. As I said I haven't been using a torque wrench, but I like to think I have a good bit of mechanical sympathy so I've not been horsing up the bolts. The lower bolt has been to the same tightness and is still fine. I have been in touch with Zipp but I don't hold out much hope.

Needless to say I've ordered a new stem AND a 5nm torque key! :oops:

g00se

Sounds like the bung is foobar if the thread is stripped.

One thing to check in the future - might have been the case here - is that the top cap doesn't foul the steerer or bung before it engages with the stem (or in the process of tightening). In which case, you'll end up torquing the top cap against the steerer but the bearing will not be loaded properly and the stem may move. This will make you torque up more and strip the thread or bust the bung.

I did that myself. The top cap have a big chamfer underneath it and this fitted inside the steerer and butted up against the bung. Tightening up the top cap just pulled the thread through the bung.