Slipping steerer bung

paulbnix

I have a Planet X Hurricane that has a full carbon steerer - branded Selcof.
I have tried two different bungs and in both cases the bung shifts up after a few rides and I then get the dreaded fork rattle.
I know it's easy just to loosen the stem, tighten the preload then tighten the stem bolts for another 2 weeks rattle free then eventually move the bung down and start again.
I have tightened the bung quite a bit - not measured the torque maybe I'll try to next time.

I want a better solution and I am thinking of aralditing the bung into the fork.

I would need to clean all the carbon assembly paste out first - yes I have used the paste.

Just trying to think what problems I could be causing for myself.

I have had a number of bikes with full carbon forks and have not had this problem with any of them. Also I cannot think of a time when I have had to remove a bung.

Ben6899

Which bungs have you tried? Could be that you’ve tried two shiit ones!

masjer

The bung is not there to stop the stem from rising up the steerer during use (only during installation). What seems to be happening is that the stem isn't gripping the steerer enough.
Have the bolts been tightened incrementally, alternating between each bolt?
Also, has the steerer been cut correctly so the stem/headset set can be preloaded during installation?

paulbnix

masjer said:

The bung is not there to stop the stem from rising up the steerer during use (only during installation). What seems to be happening is that the stem isn't gripping the steerer enough.
Have the bolts been tightened incrementally, alternating between each bolt

That's probably true.
The bolts have been incrementally tightened and I'm sure more than the 5nm noted on the stem.
So maybe my problem is more to do with slip between the stem and steerer rather than bung and steerer.

masjer said:

Also, has the steerer been cut correctly so the stem/headset set can be preloaded during installation?

There is about 5mm gap so enough to preload.

I'll clean up the steerer and stem in case there is some contamination there and have a look to see if I have a spare stem.

masjer

A clean is a good idea. It would be great if you do have a spare stem to test. It would quickly identify if the stem is the problem.

paulbnix

I've found a spare stem, cleaned up the steerer and am awaiting a few rides to see if my problem is solved.

Ben6899

If the bung is sliding as well, it could mean you're never quite achieving proper, full preload.

But see how you get on with the new/clean stem.

womack

paulbnix said:

masjer said:

The bung is not there to stop the stem from rising up the steerer during use (only during installation). What seems to be happening is that the stem isn't gripping the steerer enough.
Have the bolts been tightened incrementally, alternating between each bolt

That's probably true.
The bolts have been incrementally tightened and I'm sure more than the 5nm noted on the stem.
So maybe my problem is more to do with slip between the stem and steerer rather than bung and steerer.

masjer said:

Also, has the steerer been cut correctly so the stem/headset set can be preloaded during installation?

There is about 5mm gap so enough to preload.

I'll clean up the steerer and stem in case there is some contamination there and have a look to see if I have a spare stem.

No expert but I thought 3mm was the right gap. I cut mine to 3mm and have never had a problem.

i.bhamra

womack said:

No expert but I thought 3mm was the right gap. I cut mine to 3mm and have never had a problem.

It's unlikely to make a difference unless going from 3 to 5mm gap means the bolt is no longer long enough to engage the threads on the bung.

paulbnix

There is no issue with correctly setting the preload.
There is no movement in the fork once I set it.
It remains like that for as least a couple of rides.
When I do find the fork has started to rattle I can see that the bung has lifted by a mm or so.

My assumption was that the bung needed to be more secure to stop it lifting.
As masjer pointed out it may be that the stem clamp is not working correctly and allowing the stem and bung to lift.

Its now awaiting a couple of rides with a replacement stem and the stem bolts torqued at 5 nm.

veronese68

If that's the case it's definitely the stem that was slipping. Once you've set the preload and tightened the stem the top cap doesn't really do anything other than stop things going down the steerer tube, it shouldn't have to maintain the preload on the bearings.

webboo

I have this on one my bikes. Fork/ bung/ stem used to come loose. Changed the stem and it was a bit better but still would work loose. In the end tightened it required torque 6nm then gave another turn with the Allen key and it’s been fine.
Apparently sometimes the carbon steerer tube might not be perfectly round and this is the problem.
On my 3 bikes 2 of my stems say torque to 6nm and the other says 7nm.

paulbnix

Thanks Webboo that sounds to be a good reason for my problem steerer. It must be the cheap Px stuff 😃

webboo

I’m sure there was a previous thread on here where a couple of people stated it’s pretty hard to damage the steerer by over tightening the stem.

Ben6899

webboo said:

I’m sure there was a previous thread on here where a couple of people stated it’s pretty hard to damage the steerer by over tightening the stem.

Some good info came up in this thread: https://forum.bikeradar.com/discussion/13117200/columbus-futura-fork-3t-arx-pro-stem#latest

Btw, my outcome was fitting a new stem with the "classic" 2x5Nm bolts. Haven't ridden far yet, as it's my good weather bike. Main driver for me was that, with my Engineer's hat on, I wasn't happy with only one bolt holding the stem onto the steerer!

darkhairedlord

you might problems in the long term if you have used carbon assembly paste. I would avoid on the stem to steerer interface.

paulbnix

I've had my first ride and the steerer is still solid.

I don't normally use my torque wrench for the stem bolts but just use a small Allen key as it naturally limits the torque you can apply.
Anyway I checked the stem bolts with my Allen key after using the torque wrench and they were a lot tighter than before.

I wonder if this could have been the problem either this particular steerer.

joeyhalloran

highly likely as it's the stem that keeps the headset coming loose. If the stem moves then you're just relying on the fork bung/steerer cap.

paulbnix

I've now cycled about 150 miles with the replacement stem and the torque increased to 7 nm and there has been no movement of the bung so the fork has remained rattle free.

Sorted.

wongataa

paulbnix said:

I've had my first ride and the steerer is still solid.

I don't normally use my torque wrench for the stem bolts but just use a small Allen key as it naturally limits the torque you can apply.
Anyway I checked the stem bolts with my Allen key after using the torque wrench and they were a lot tighter than before.

I wonder if this could have been the problem either this particular steerer.

It probably was the problem. There is a reason why torque settings are given - to make sure things are tightened up enough and not too much.

MattFalle

wongataa said:

paulbnix said:

I've had my first ride and the steerer is still solid.

I don't normally use my torque wrench for the stem bolts but just use a small Allen key as it naturally limits the torque you can apply.
Anyway I checked the stem bolts with my Allen key after using the torque wrench and they were a lot tighter than before.

I wonder if this could have been the problem either this particular steerer.

It probably was the problem. There is a reason why torque settings are given - to make sure things are tightened up enough and not too much.

#inspired

paulbnix

Wongataa could be right, it's just never been an issue on previous bikes.
Forceful hand tight has been enough.

I'm now using 7nm although the stem says 5.