[Closed] How to stop my bars twisting?

Are you torquing to the exact spec required for the stem bolts? Other than that carbon paste is worth a go.

To be truthful I am relying on the good old "hairy arm" torque wrench method. Which may in inself be an issue, although I've yet to experience this problem with various other alu stems and steerers.

Could be worth seeking out a torque wrench just in case tho 👍

Sure you haven’t stripped one of the bolts already?

Good thought but yes, fairly sure, I'm not all that ham-fisted as a rule! 😄😳

Bit confused - you said the bars twist in the stem but also it's the stem-steerer interface?

To be sure on terminolgy (sorry if this is granny-eggs)..... the steerer is the tube that goes through the frame and is part of the forks. The stem is attached to this and points forwards. The bars are....well..... but held in the front of the stem by the faceplate, usually a detachable 2 or 4 bolt thing.

My first thought is that you don't have the bolts tight enough, but also when tightening do you do them bit by bit alternately, so they all share the load?

And another option - if it's the bars twisting; some bars have a different diameter to others, you don't have a mismatch in bars and stem?

Sorry, yes, my description was not super clear 😐

The rotation is the stem about the steerer, if that makes sense? So the bars twist relative to the front wheel.

When tightening I do nip the bolts (two of them) up alternately in order to share load as you say.

The stem itself has a smooth/shiny finish (Funny Funduro FWIW) which may not be helping. I did wonder about roughing it up on the inner face, although that seems a bit drastic.

Do you use carbon friction paste? Try a bit on the inner surface of the stem. Tighten it to the required torque.

Hopefully that may help!

Yes tighten them equally and alternately so it evenly clamps.
Those sort of low stack height stems have a small clamping area so the right torque is probably more important than ones with a big clamping area.

Is it a new stem or, new to you? Perhaps try it on another fork and see if it slips on that? It could well be a manufacturing fault on the stem, too large a diameter- it has been known!
Hope this helps.

A torque wrench can be worthwhile as some stems require a lot more than others. For example my RaceFace Turbine needs over double that of my Thomson X4. Friction paste works well but I've never needed it on a steerer. Are the bolts nice and clean and moving freely? If they're stiff they might require more effort whilst not actually tightening that much.

Maybe not what you want to hear but I would change the stem (after checking the Google and confirming by suspicions).
I had a RaceFace stem with the same cut outs around the steerer and that would move too much. I swapped it out for one that had a better interface between the stem and steerer and had no more issues.

I wonder if there a manufacturing flaw stopping it closing up properly. Can you see a full gap in the slot? I'd be tempted to take it off, take the bolts out, then run some sandpaper or emery through the slot. Or just nip it up some more, maybe you aren't as strong as you like to think 🙂

Thanks folks.

I'll take it off and double check the bolts are moving freely and the slot is clear. I can actually measure the ID with calipers so I can double check that too.

Hopefully it's not just the stem itself: I'm not flush with stack height on this fork, plus the stem was a good deal 🤣 (although admittedly less so if I have to buy another!). I'll probably try fibre paste before outright replacing it.

Cheers all 👍

If nothing works or it's made out of tolerance and you have to replace it, the dmr defy is a good solid low stack option.

I’m not flush with stack height on this fork

I'm not sure what you mean by this? Stem needs to sit slightly proud (above top of steerer) so you've got room for the stem cap. But, is the top stem tightening bolt also sitting above the top of the steerer? If it is, then when you tighten it it will only be tightening thin air!

Wipe steerer with a clean rag, remove the stem bolts, clean, apply a liberal amount of grease to all their articulating surfaces and then reinstall using a torque wrench to evenly nip up to the specified torque.

If it is, then when you tighten it it will only be tightening thin air!

Tee hee, yes, I can imagine it twisting quite readily in that scenario! 😆

I am onboard with what you say and thank you for pointing it out.

What I meant by "I’m not flush with stack height on this fork" is that I have relatively little protruding steerer, so wanted a relatively low stack stem, esp. one that isn't silly money!

Disappointed that a 'new fork' hasn't been suggested 😁 yet.

But I think the OP has the measure of it now, so good luck with your fault finding. Must admit if you have to resort to carbon paste, it doesn't bode well.

Is a Thomson stem? 6mm thread with 4mm Allen key heads or similar?

Firstly, there should be no grease on the steerer/stem interface. Clean, degreased with no burrs or imperfections that could lead to uneven distribution of the clamping forces. The steerer should be a good fit in the stem prior to tightening. The recommended torque on the bolts for example a Thomson stem are 5.5 Nm which is 4Ft/lbs. (This is under half of the torque that even a low grade 8.8 grade bolt can withstand) Each bolt tightened repeatedly in turn until both are at recommended torque.

Tightening the bolts further can increase the clamping force but if taken too far damage the threads in the stem or lead to distortion. I can't say I recommend doing this but admit to having done it myself as I've experienced similar problems.

Good luck.

Grease the threads of the bolts and try again.

Once upon a time, I may have tightened bolts to the extent that the clamp part of the stem stretched a little bit.

Yes, I’d expect the bolts to round off or snap first but they didn’t.  Good tools and a steady if gorilla like hand.

Are the faces of the clamp where the bolt passes through parallel?  If they are closer further from the steerer then your stem may be due for replacement.

Stem needs to sit slightly proud (above top of steerer) so you’ve got room for the stem cap.

Or add a 3-5mm spacer above the stem to maximise clamping area.

If it was tight before and won’t tighten enough now I’d say stretched bolts too

Just give the bolts a bit more Welly. I have a funn stem on my eeb and it's not moved in plenty of crashes!

Try a torque wrench (but don't ignore your senses completely...torque wrenches are much longer so if you miss the click or set it wrong it's easy to strip stuff.

Check the bolts are not too long and bottoming out, or if open ended, that the threads are not binding (screw the bolt on from the wrong side to check)

So I had a chance to look at the stem yesterday.

Fwiw it is a new stem (Funn Funduro) and all looks nice visually. Bolts look fine, slot has plenty of space to allow clamping and has (visually) parallel faces. No burrs or anything funny.

During disassembly one oddity: the spacer above the stem wouldn't come off, which made me think "oh crap oval steerer". On inspection though the stem has some little shoulders where the spacer sits that the (relatively thick) spacer was fouling on slightly, and it had wedged against them.

Other than that everything looked fine.

So I cleaned everything, greased the bolts, and put it back together with a thinner spacer on top.

Am riding it later so hopefully all is fine 🤞

Thanks again everyone for your suggestions.

hopefully all is fine

I assume you’ve done the “hold the wheel between your legs and try and turn the bars” test before riding?

The last place you want to find out if this hasn’t worked is when actually riding.

It sonds as though the stem was actually partly clamping on the spacer. This would certainly reduce it's grip on the steerer.

I've had that with a 1" steerer shimmed out to take a 1 1/8th stem. The spacer under the stem was small enough to slip into the stem when it wasn't tightened, which then prevented it clamping onto the shim/steerer properly...

Took me an embarrassingly long time to work it out. (Couple of hours of head scratching and about 4 cups of tea)