Expander plug in a carbon steerer tube

arthur_scrimshaw

Evening

I've got a terrible creaking when I'm out of the saddle or using the front brake so decided to strip down the headset as the noise seemed to come from that area. Cleaned and re greased everything but when I was reassembling the stack I noticed the expander plug was set way down in the steerer, well below where the stem clamps the steerer tube.



I know the primary purpose of the bung is to preload the bearings but I thought in a carbon steerer the bung also served to prevent the stem from collapsing the steerer?
It's been like that since the shop cut the steerer down and I've done a few thousand miles and not died yet? Is it ok or should I be worried?
Bike is a carbon synapse.

To cap it all I've still got the bloody creaking, looks like its the disc brake?

wongataa

The expander plug is there just so you can load up the headset bearings like the star nut for metal steerer tubes.

timothyw

Picture isn't loading for me at the moment FYI.

My view is that although it isn't vital that the bung sit where the stem is, it's certainly desirable, so if you have means to adjust it so that it lines up better with the stem (or another expander in the parts bin that might do the job better) then it isn't a bad idea.

As with so much else in cycling though, how much of an issue this is depends on the type of riding you do, and what sort of rider you are - clearly it's likely to be more important for a powerful sprinter to reinforce the clamping point than for a 60kg mountain goat, or a leisure rider who rarely gets out of the saddle.

svetty

Different manufacturers have differing advice and guidance about this. The bung should ideally be - as you say - sited at the level of the stem to both enable preloading and to resist the stem clamp crushing the steerer. In reality the steerer is strong enough that it can absorb road impacts and unless you over-tighten the stem clamp it is most unlikely that you will have a problem. Still, if you can re-site the bung I'd do so.

arthur_scrimshaw

Thanks for the replies - can you see the pictures now? I think I may have solved it - the top cap is not just a cap but a series of discs with run down about 50mm and I presume these internally support the steerer from being crushed?

svetty

Arthur Scrimshaw wrote:

Thanks for the replies - can you see the pictures now? I think I may have solved it - the top cap is not just a cap but a series of discs with run down about 50mm and I presume these internally support the steerer from being crushed?

Yes, it's those that support the stem.

arthur_scrimshaw

Cheers, mind now at peace!

rnath

Re. original post, don't know if you solved your creak but in case it helps I had a similar problem. After repeatedly rebuilding the front end over several months and going slightly insane trying to track it down, it turned out to be the front skewer simply needed regreasing. Just never occurred to me.

arthur_scrimshaw

rnath wrote:

Re. original post, don't know if you solved your creak but in case it helps I had a similar problem. After repeatedly rebuilding the front end over several months and going slightly insane trying to track it down, it turned out to be the front skewer simply needed regreasing. Just never occurred to me.

I did in the end!

After eliminating the headset I did exactly what you suggested and it still creaked!
I then cleaned the brake pads and that sorted it :oops: - occam's razor lesson learned.