Stem will not tighten up

[Boogz83]

Got a strange one with my cube 144 and nuke proof stem. All adjusted spot on steerer sits 3mm below the stem and headset adjusts spot on, stems bolts torqued but after a few hours of riding play develops in the headset and if you hold the front wheel and twist the bars hard they move.
Clearly the stem is not gripping the steerer despite the steerer being clean, ruffed up with sand paper and all torqued correctly!
Anyone else ever has issues like this?

 

[Joecrow]

Clearly the stem is not gripping the steerer despite the steerer being clean, ruffed up with sand paper and all torqued correctly!

Only thing I can think of is to check your torque wrench is accurate.

 

[Boogz83]

Only thing I can think of is to check your touque wrench is accurate.

Yes it’s spot and and the bolts are tight I certainly wouldn’t want to go any tighter

 

[irie]

First thing is check that both the steerer and stem are exactly circular and matching diameters.

Then use a fine smear of "Park Tool SAC-2 Supergrip Carbon and Alloy Assembly Compound" (or equivalent) on the inside of the stem. "Fine" means exactly that, too much and you won't get the stem onto the steerer.

 

[levity]

When tightened can you see a gap where the stem sides come together? If not perhaps they are making contact preventing them from clamping tightly on the steerer tube. You may need to file or sand a bit off from the two surfaces to allow them to pinch more tightly.

 

[Boogz83]

I wonder if it’s a faulty stem, just removed a spacer so the steerer goes about 2mm above the stem and it grips spot on.
It may be I just have to run a small spacer on top of the stem

 

[irie]

I wonder if it’s a faulty stem, just removed a spacer so the steerer goes about 2mm above the stem and it grips spot on.
It may be I just have to run a small spacer on top of the stem

Assuming the steerer tube is OK then it sounds like the stem top bolt is too near the top of the stem. Which would be fixed as you say above with a 5mm spacer on top of the stem.

 

[Funkeydunk]

I agree with Irie above, two things I would check:
is there really sufficient gap between the top cap and steerer tube
as you’re tightening your top cap is the star nut being pulled out.
one bonus suggestion is make sure your headset bearings and expanders are all seated correctly.

 

[Paulquattro]

I agree with Irie above, two things I would check:
is there really sufficient gap between the top cap and steerer tube
as you’re tightening your top cap is the star nut being pulled out.
one bonus suggestion is make sure your headset bearings and expanders are all seated correctly.

This wouldn't stop the clamp of the stem working thou as he says he can twist the bars
It would cause issues adjusting the play out of the bearings thou obviously
But the OP specifically mentioned there bars twisting on the steerer .
What might help is some pics of the job so we can see whats going on

 

[Boogz83]

Hi thanks for everyone’s reply’s it’s appreciated. It’s all adjusted spot on and the star nut doesn’t slip it’s the stem.
It would appear it’s a known issue with the nukeproof stems being slightly machine wrong.
I think I’ve got around it by removing on of the lower spaces making the steerer go all the through the stem and then placing a spacer on top making the clamping area bigger. Fingers crossed anyway

 

[Paulquattro]

Hi thanks for everyone’s reply’s it’s appreciated. It’s all adjusted spot on and the star nut doesn’t slip it’s the stem.
It would appear it’s a known issue with the nukeproof stems being slightly machine wrong.
I think I’ve got around it by removing on of the lower spaces making the steerer go all the through the stem and then placing a spacer on top making the clamping area bigger. Fingers crossed anyway

Glad you have a result but they obviously over sized the bore of the stem to much from what you are saying
please keep a close eye on it as for me it would be a replacement as i could not use it knowing its not clamping properly
A new stem would be better for me than a potential injury

 

[Jeromep]

A machining size issue would certainly be a problem. Just my guess, but that seems unlikely. I would think Nukeproof outsources that to a company who specializes in producing these parts. Did you use assembly grease (with the carbon fiber grit in it, or regular grease … without the grit)?

 

[John Beedham]

You’re loading the headset bearing with the wheel on the ground …. If not that will be the problem ….. maybe ‘will’ is over confident …. May well!