Bicycle Mechanics - Compression nut slides within steerer tube

Hello all,

I recently noticed that the fork on my '05 Specialized Tarmac is ever so slightly loose. I loosened the stem bolts and went on to tighten down the cap bolt to eliminate the slight fork play. Upon tightening the cap bolt I noticed that the compression nut was sliding up the steerer tube enough so that adequate bearing pre-load cannot be achieved. The head set is an FSA and the compression plug is a series of expanding wedges held together by a rubber o-ring.

It looks to me like the compression plug is not expanding enough to adequately wedge itself into the steerer tube. Do I need a new one or is there a trick to get it to work correctly? I can't imagine that my head set bearings are worn out...

Thank you all!

JT

PS: I did a search on this topic and found nothing that directly addressed my problem. I was however able to verify that the assembly/adjustment sequence that I have used is correct.

Are you sure the compression plug does not have another allen screw to tighten to lock the plug in place before you pre-load?

+1

5 and 6mm allens

If it still slips, try some carbon prep. But if you are torquing it enough to pull the compression plug out, you must have something wrong with the headset.

is it actually 'slipping upwards' or is it compressing everything together, then bottoming out on the top of the fork steerer? the latter is pretty common, you usually fix it by putting a 5mm spacer between the top of the stem and the compression cap.

--brett

First off, there is only one bolt that comes into contact with the compression nut (c/n) and that is the Allen bolt that goes through the cap on the top on the stem.

Secondly, when I installed the c/n-cap-Allen bolt assembly, I made sure to install the nut onto the end of the bolt by just a few threads, this in order to ensure that the c/n slid far enough down the steerer tube to not come into contact with the bottom of the cap upon tightening of the bolt. When I tightened the bolt though, little effort was required to get the c/n to rise through the steerer tube to the point where it actually come into contact with the cap.

I then removed the c/n, disassembled it, reassembled it and repeated the process. The second time I was able to get a small amount of pre-load on the bearings and proceeded to tighten the stem bolts. The fork has subsequently loosened.

It seems that I need a c/n that will grip the inside of the steerer tube better. That or I modify the existing c/n to grip better...

Thanks!!

JT

I used carbon prep and my compression plug stopped slipping

I used carbon prep and my compression plug stopped slipping

Hmmm....looking on Google right now. Thanks!

I used carbon prep and my compression plug stopped slipping

+1

Try greasing the internal wedging surfaces of the plug as well as the threads, but keep the exterior clean and apply either the Tacx carbon prep Nitro recommended (especially if the steerer is carbon), or anti-seize compound to the exterior surface for aluminum or steel steerers. The point is to not use any lube on the outside of the plug to allow it to grip and compress, yet leave something on the outside to prevent corrosion and seizing.