Headset - A rattling good fit!!

[wotnoshoeseh]

Hi all,
I've got a bit of an issue with the headset on my GT Series 4. It's one of these new fangled headsets (well new to me) that has 2 pinch bolts for the stem/steerer and a cap screw on the top for tightening.
It went loose previously and I had the PB people fix it when I brought it in for one of their free check ups.

Recently though it came back and I followed the procedure to fix it. Loosen the pinch screws on the stem, and tighten the top cap screw. No problem, all the rattles went away. However every time I go over rough ground the rattle comes back. I need to carry a 4mm. Allen key with me all the time.

Anyone got any ideas how I fix it permanently or if there is something else I need to be checking for?

Thaks,
D.

 

[dabac]

All threadless headsets I've come across have used a conical shim/bushing to center the steerer tube in the top bearing. If this piece goes missing the steerer tube can rattle in the top bearing. Cranking down on the top cap might keep it in place while lightly loaded, but isn't enough for rougher riding.

 

[wotnoshoeseh]

Originally Posted by dabac .

All threadless headsets I've come across have used a conical shim/bushing to center the steerer tube in the top bearing. If this piece goes missing the steerer tube can rattle in the top bearing. Cranking down on the top cap might keep it in place while lightly loaded, but isn't enough for rougher riding.

Thanks dabac. What do you mean when you say "go missing". No longer fitted? Lost? Has come loose? It can't have gone missing though - I've never had the headset dis-assembled.

Thanks,
D.

 

[alfeng]

While it is true that most threadless headsets have a "centering cone" of some sort or another, the obvious exception is a CHRIS KING headset ... Some centering cones are plastic, some are metal -- regardless, I think it is probably difficult for the piece to actually disintegrate ... and, if it is absent then it means that it was probably lost. (i.e., not installed) ...

• The reason a centering cone is necessary is because of inner diameter of most cartridge bearings is larger than the outer diameter of the fork's steerer.

In the case of headsets with "loose"/(caged) bearings, the centering cone serves the same purpose as the small "cone" on the crown race AND/OR the cone in a hub which has loose bearings.

 

[tafi]

The main cause I have seen for headsets frequently loosening, is a steerer expander/binder which is not tight enough in a carbon steerer or a starnut which has not "bitten in" properly on an alloy steerer. These pieces are the parts which sit inside the steerer tube and the the top cap screw threads into them. If they are not bound to the steerer properly then they will slowly be pulled upwards by a combination of rough roads and periodic retightening of the top cap, which can cause the headset to loosen. Eventually they can get pulled out the top of the steerer tube.

The solution is to ensure that they are

1) inserted deep enough in the steerer
2) are tight enough: In the case of a binder nut this means tightening the expander hard against the internal walls of the steerer so that friction is high enough. In the case of a star nut this means using a proper starnut punch and possibly also getting a mechanic to check that the starnut's "leaves" actually dig into the inside wall of the alloy steerer. If not then the use of a metal working punch can sometimes get them to do so.

 

[FBinNY]

A common source of frequent loosening of new headsets or (headsets on new bikes) is incomplete seating of the crown race. You adjust the headset then after a bit of riding the crown race settles a bit on the fork loosening the adjustment. Look at the top of the fork below the headtube and see if there's a gap below the crown race. If there is, have the shop tap it down and seat it properly.
The bright side is that if it is a poorly seated race it'll fix itself eventually as it works it's way to the bottom, after which there'll be no more headset adjustments.

The other possibilities include those listed above, a missing or poorly fitted centering cone, or a stem clamp that slips, though I doubt the latter unless the bike is subjected to very rough service.