Carbon Steerer Expander Bung - Torque Setting?

arlowood

Built up several steel and Alu frames over the past 3-4 years but just about to start my first carbon frame build after bagging a PX Pro Carbon frameset in the "Clearance Sale" a month or so back.

Now equipped with a shiny new torque wrench which I've never had to use previously.

However after a bit of googling I've not yet found any definitive guidance on what torque should be used on the installation of the carbon steerer bung. I know I could employ trial and error eg - pick a setting then install stem (without tightening the clamp bolts) and try to set bearing pre-load. If this fails and the bung moves then up the torque setting and try again

Would like to try and avoid that by doing a once and for all installation.

Also, what's the received wisdom on whether to use assembly paste on the inside of the steerer to anchor the bung more securely. Yes/No/Maybe?

nicklouse

there is not one and can never be one.

tight.

svetty

The correct torque is the amount needed to correctly ensure there is no play in the headset - and no more. Once the stem bolts are then tightened the top cap torque is irrelevant. The bung shouldn't creep up the steerer if is installed properly using carbon paste.

If you are needing excessive torque to elminate play in the headset something is wrong somewhere. Either there isn't enough gap between the top of the steerer tube and the edge of the top spacer (should be 3mm approx), or you need to shim the conical top bearing cap so it isn't bottoming on the head tube.

nicklouse

Svetty wrote:

The correct torque is the amount needed to correctly ensure there is no play in the headset - and no more. Once the stem bolts are then tightened the top cap torque is irrelevant.

the OP is asking about an expander bung. top the top cap. (though that can be part of it) but again that has no torque setting either.

svetty

nicklouse wrote:

Svetty wrote:

The correct torque is the amount needed to correctly ensure there is no play in the headset - and no more. Once the stem bolts are then tightened the top cap torque is irrelevant.

the OP is asking about an expander bung. top the top cap. (though that can be part of it) but again that has no torque setting either.

I've edited/expanded my post to try and clarify

Monty Dog

Assembly paste helps the bung grip better and need for a tighter torque - you just need enough to keep it snug. The main purpose of the bung is to stop the steerer being crushed by the stem, as well as allowing headset bearing adjustment. If the headset works loose, then it only takes a few minutes to re-adjust.

mugensi

Monty Dog wrote:

Assembly paste helps the bung grip better and need for a tighter torque - you just need enough to keep it snug. The main purpose of the bung is to stop the steerer being crushed by the stem, as well as allowing headset bearing adjustment. If the headset works loose, then it only takes a few minutes to re-adjust.

I would have thought that the main purpose of the bung is to give the top cap something to screw into in order to clamp down the stem/pre-load the headset bearing...non?

daniel_b

Can't answer the exact question relating to this bike, but on my Scott, I found an online video where they specify 8nm - I tried this, and wowsas it did make me wince a bit, but it hasn't budged.

This is the vid I located:
https://www.youtube.com/watch?v=cQe9TJJq1PE

Different frame and expander of course, so no idea if that is too much or too little, but might give you something to start with.

keef66

On my Scott I tightened it by hand / allen key. Initially just enough to keep it in place when adjusting headset preload. Then after a couple of shake-down rides and some adjustment, once the stem was tightened around the steerer I took off the top cap and nipped up the steerer bung a bit more. Top cap is irrelevant after that but I put it back on to keep the rain out

arlowood

Daniel B wrote:

Can't answer the exact question relating to this bike, but on my Scott, I found an online video where they specify 8nm - I tried this, and wowsas it did make me wince a bit, but it hasn't budged.

This is the vid I located:
https://www.youtube.com/watch?v=cQe9TJJq1PE

Different frame and expander of course, so no idea if that is too much or too little, but might give you something to start with.

Hi Daniel

TKS for that - had found that video earlier but didn't watch it all the way through so missed the comment about torquing the plug fixing bolt to 8Nm.
I'm using a Zenith expander bung courtesy of Malcolm at Cycleclinic who swears by them. Torque setting should be in the same ball park so I will have a go at 8Nm to begin with.

Anonymous

I've also heard 8NM

daniel_b

arlowood wrote:

Daniel B wrote:

Can't answer the exact question relating to this bike, but on my Scott, I found an online video where they specify 8nm - I tried this, and wowsas it did make me wince a bit, but it hasn't budged.

This is the vid I located:
https://www.youtube.com/watch?v=cQe9TJJq1PE

Different frame and expander of course, so no idea if that is too much or too little, but might give you something to start with.

Hi Daniel

TKS for that - had found that video earlier but didn't watch it all the way through so missed the comment about torquing the plug fixing bolt to 8Nm.
I'm using a Zenith expander bung courtesy of Malcolm at Cycleclinic who swears by them. Torque setting should be in the same ball park so I will have a go at 8Nm to begin with.

Cool, let us know how you get on - I have to put one in to my Exocet 2 when I eventually get around to building it up!