Columbus Futura fork / 3T Arx Pro stem

Ben6899

Would like some opinions, please!

Got a Columbus Futura fork on my steel bike. Carbon steerer - paperwork says max stem torque should be 5Nm.

Also got a 3T Arx Pro stem, the one with the single Torx bolt. Printed on the stem is Max Torque 8Nm.

Never had any trouble with this setup until I dismantled the front end recently, to travel. Reassembled everything, using 5Nm on that single stem Torx bolt.

The headset keeps losing preload. I know how to preload a stem and what to look for when having problems, such as slipping bung or insufficient steerer/bung clearance to the preload cap. All of that is fine.

I’m asking myself the question now “do I creep closer to that 8Nm?” and “do I actually need to because there’s only one bolt?” although the bolt does influence a larger surface area of the stem so one would think there would be sufficient “grip” at 5Nm.

Cheers!

whyamihere

Have you got carbon paste between the steerer and the stem? If not, that will help it grip with the lower torque. It may be that if you had some on before the disassembly, it needs a bit more applied as some could have been wiped away.

Ben6899

I thought about assembly paste, did some reading, and the consensus seemed to be that you shouldn’t put it on a steerer?

Jury is open for me though - it’s a good idea. I might buy a tube.

whyamihere

Anecdotally, I've never had a problem. Just a small amount, ideally applied to the inside of the stem rather than on the steerer so that any excess is pushed out the top rather than down towards the headset. I imagine it could cause problems with the headset if you squirt loads on and let it get down into the bearings, but if you're sensible with it it seems to be fine.

Ben6899

*sigh*

I've just dropped the fork out to give everything a clean before reassembling (with a touch of fibre grip) and there's a very slight "witness mark" on the steerer from the compression ring.

1. I'm not sure how this might have happened - the loosening headset has only been a thing recently and I have barely ridden the bike since it first started occurring (also adjusting the headset mid-ride with a Silca pocket torque wrench)

2. Has anyone else seen this on their carbon steerer and, if so, how bad and have you scrapped the fork? I don't recall seeing this kind of thing on previous carbon forks I have owned.

3. It looks like it *might* be in whatever coating is applied to the carbon after moulding - chances?

Ben6899

I took some photos. Feeling a little bit better after having another look…

webboo

I don’t think I would have even noticed that and if it’s damaged and weakened the steerer I would be amazed. On one of my bikes an Orbea if I tighten the stem bolts to the required torque, the headset comes loose. When this happened the first couple of times, the dealer changed the stem which improved it slightly. However it continued to occur so it got tightened without using the torque wrench and it’s been fine.
As a caveat the mechanic who advised is an aircraft engineer who has a lot of experience with carbon fibre. He reckons you it would be hard to crush tube or damage it from over tightening. You are more likely to damage it from a loose headset.

masjer

The marks on the pics above are perfectly normal. They can become slightly indented with time but, still, not a prob.
Since the stem clamp bolt has only one bolt, I'd imagine you could go slightly higher than 5NM. One M7-8 bolt at 5NM must have less clamping force than two M5 at 5NM.
Have you tried greasing the clamp bolt? A dry bolt (increased thread friction) will not impart as much clamping force as a lubed one (grease or anti-seize)

masjer

Oh, some manufactures don't recommend grip paste- because of possible abrasive action during use. I'd possibly try without.

Ben6899

Thanks for the input, @webboo and @masjer , much appreciated.

I'll hold back on riding with the grip paste on there, for the time being, and see if greasing the bolt helps. Might also go to 6Nm...

veronese68

Do you have an expander bung that is inside the tube where the stem clamp is? If so clamping it up tighter can't do any harm.

Ben6899

veronese68 said:

Do you have an expander bung that is inside the tube where the stem clamp is? If so clamping it up tighter can't do any harm.

Yeh, just the 3mm spacer above the stem so bung behind the clamp area. Slammed innit.

darkhairedlord

Ben6899 said:

I took some photos. Feeling a little bit better after having another look…

The wear (witness mark) on the steerer tube might be preventing the tapered ring from sliding down beyond the point or wear. I had this and ended up needing a new fork (although mine was way worse than this). I would avoid using a metal tapered ring and go for polymer type as it is less likely to snag on the wear lip and less likely to induce further fretting on the steerer. PS don't use carbon paste or it will get in the bearings or, worse still, the interface between the taper and the steerer.

masjer

One other thing I forgot to mention. Make sure the inside of the stem and top of the steerer are thoroughly cleaned. Isopropyl alcohol, if you have any, or degreaser.

Good luck.

Ben6899

I don't think this is an issue yet, @darkhairedlord - there's actually very little to feel so I don't think it is snagging. A polymer ring is a good idea though - can't hurt.

Think I have some stuff which will thoroughly clean the steerer.

pinno

It is negligible. Don't worry about it.

Ben6899

Columbus have written back and suggested using a different stem with 5Nm torque spec. “For safety”.