This stem here:

http://www.on-one.co.uk/i/q/STOOCNC/on-one-ultralight-cnc-stem

There doesn’t seem to be any writing on the stem itself, and there is no manual on the OO site.

I’m guessing it’s similar to other stems, but I’d like to know what others are using.

I’ve gone for 5nm on the bar bolts, and have had no issues, and would not want to go higher as I’m running carbon bars.

I’ve torqued the steerer tube bolts up to 6nm, but this doesn’t seem enough, as I’m running spacers both above and below then stem, and after riding the spacers below the stem become loose (you can spin them round with your fingers) while the spacer above is rock solid. This results in loose headset bearings.

If I loosen and retighten the steerer tube bolts the bearings are now ok.

Can I use more than 6nm without damaging a carbon steerer tube?

I don’t know. Probably?

But you could try some finish line fibre grip before you start upping the torque.

Cheers, I didn’t think of using some carbon paste, I don’t own any so will order some.

I did find some torque ratings eventually:

http://www.on-one.co.uk/old-help/guides/torque-settings

“SL Pro Carbon Road Fork Steerer to Stem Clamp: 5Nm to 8Nm”

I’m not running the exact same forks, but it looks like I can try a little more torque without any issue.

If it takes a 4mm Allen key it’s pretty much 5Nm every time. I’ve got a preset 4mm torque tool especially for this.

Yep, 5Nm

I may be a bit old skool, but if it slips then it’s probably not tight enough.
HTH.

Thanks all, I’m not sure if it’s a good idea using carbon paste on a steerer tube, as it’s got gritty bits in which may get into my headset bearings.

Yep it is a 4mm allen key, I’ll stick to 5nm, and I’ll try tightening up the top cap a little more in order to prevent movement.

I know it’s not the best way, but I’d rather avoid a crushed steerer tube.

I am pretty sure carbon paste isn’t recommended on steerer tubes – definitely not on carbon steerers. Are you sure the play in the spacers didn’t come from the bearings settling into the frame by a tiny amount? Like you suggest tighten the top cap abit and then retighten the stem, 5Nm will be fine.

I’ve used these stems for a few years.

I always use a 5nm torque-key for the bar plate bolts (plus have carbon bars).

For the steerer bolts tbh I just tighten them so they don’t slip. But, for your lower spacer to be loose I’d be looking at how you pre-load the bearings first.

What headset are you using, for example if a Hope have you the 3 shims installed?

No idea on torque settings as I’ve never used a torque wrench on a bike. But as far as the loose headset, I’d suspect some other issue as said above. I can imagine twisting stem with too low torque, but to loosen headset the top cap must loosen and the stem is going to have move vertically. Have you checked the spacer underneath the stem is making full contact with stem and headset?

Have you tightened the carbon steerer plug in steerer tube first, expand it to grip, then preload the top cap and tighten the stem bolts.

I am pretty sure carbon paste isn’t recommended on steerer tubes – definitely not on carbon steerers. Are you sure the play in the spacers didn’t come from the bearings settling into the frame by a tiny amount? Like you suggest tighten the top cap abit and then retighten the stem, 5Nm will be fine.

I’ll forget the paste then, thanks.

The headset bearings did settle a little after installing the stem, but I did the usual loosen the stem bolts, tighten down the top cap a little, then re-tighten the stem bolts. I’ll try again, but if I do any tighter with the top cap bolt I can feel it’s a little too tight as the bearings feel tight.

I’ve used these stems for a few years.

I always use a 5nm torque-key for the bar plate bolts (plus have carbon bars).

For the steerer bolts tbh I just tighten them so they don’t slip. But, for your lower spacer to be loose I’d be looking at how you pre-load the bearings first.

What headset are you using, for example if a Hope have you the 3 shims installed? I’m using the Gusset Mix and Match Headset (http://www.wiggle.co.uk/gusset-mix-and-match-headset/), which is pretty much the same as the Hope Pick and Mix. I have all 3 shims in there also.

I’ll try some more pre-load, maybe I’ve got to have it a little tight, then it will loosen after a ride or two.

No idea on torque settings as I’ve never used a torque wrench on a bike. But as far as the loose headset, I’d suspect some other issue as said above. I can imagine twisting stem with too low torque, but to loosen headset the top cap must loosen and the stem is going to have move vertically. Have you checked the spacer underneath the stem is making full contact with stem and headset?

I’ll try some other spacers, but when they are a little loose you can rotate them around the steerer with, and they feel that they are even, and making full contact.

I used to not use a torque wrench, but with these carbon bits I like to use one. Often too little torque can be as bad or worse than too much.

Have you tightened the carbon steerer plug in steerer tube first, expand it to grip, then preload the top cap and tighten the stem bolts.

Yep, bung already in, expanded, and the stem is clamping on the part of the steerer with the bung as far as I can tell.

I think I may just need a little more pre-load, the weather is amazing today, so I’ll go for a quick 30 min spin and see how it goes. 🙂

Thought the standard was to add thread lock tighten it up until it strips the thread then back off a 1/4 turn. 😐

Is it a new build? Are you sure the stem slipped on the steerer? It seems more likely that some bearings / press fit interface has ‘settled’ with a bit of riding.

My guess is that you’ll preload it again, tighten to 6nm again, and it’ll never budge.

I would definitely use carbon paste though. Wipe off any excess and it won’t go into your headset.