star fangled nuts

[mig]

in steel steerers. what is the recommended depth at which these should be please?

i have a bike with a 'hard to adjust' aheadset in which the SFN is set merely a few mm from the top of the steerer. this seems to be wrong to me.

[andrewjoseph]

I think it should be about 2 cm from top, but length of bolt will have some bearing.

[531colin]

Surely the SFN only needs to be inserted deep enough so the bolt pre-loads the bearing, it doesn't bottom out on the SFN first?
Steel steerers are not famous for breaking, but why not avoid a situation where the SFN is situated in a stressed part of the steerer, ie the bit where the stem mounts?
Also, either the stem, or a spacer above the stem, needs to be above the end of the steerer, otherwise the top cap bears on the steerer, not the bearing.

[Brucey]

if you think the top cap is bottoming out then try a different top cap or a spacer beneath the top cap.

I don't like SFNs at all really. The marks they leave inside the steerer to me look just like the kinds of feature that might start a fatigue crack.

If you think the steerer is stressed where the stem clamps on it you would be right (and it varies with the stem design), but the part just below the stem sees much, much more bending stress. With the exception of those which are damaged through using the wrong kind of stem or an overtightened stem, A-Head steerers that break (anywhere near the top) normally break just below the stem or somewhere near the top race.

BTW there are such things as top caps which have a recess in them that allows the steerer to protrude beyond the stem slightly. I have no idea where to buy them these days which is a shame, because I much prefer the steerer to protrude slightly if it is a fragile (e.g. carbon) one, and a single piece looks far neater than a top cap plus spacer.

cheers

[NATURAL ANKLING]

Hi,
I was dimantling one of my skip bikes for parts
I have no (not much) previous experience with threadless headsets / forks.....really, only with the skip bikes I have bought and my skip trainer.
Well the head cap is plastic and the USELESS NUTSERT was going round and round, so you cannot dismantle the forks from bike unless you trash the real cheap (Apollo ((Halfords Own)) plastic top cap
I like to keep all the bits
So I just drifted the SFN out with a rod thru the hole in base of steerer above tyre, Easy.

Mount SFN in the steerer where the stem clamps but at least 1cm from edge of stem.
SFN damage the steerer tube The steel is harder than steerer tube as its spring quality steel, but damage that much considering that not much tension is needed on the top bolt
Maybe in the hands of ham fisted morons.

[Brucey]

...SFN damage the steerer tube The steel is harder than steerer tube as its spring quality steel, but damage that much considering that not much tension is needed on the top bolt
Maybe in the hands of ham fisted morons.

In normal use there are tens of kg load on each petal of the SFN, and they have very sharp corners. Of course they dig in, it is how they work....! No morons required, ham fisted or otherwise....

I have seen much less worrying-looking scratches than those produced by SFNs turn into fatigue cracks.

One of the few things that might mitigate the situation is that the residual stresses around the damage may not be as harmful as they could be if the same notch was made by other means.

cheers

[NATURAL ANKLING]

Hi,
Surely you must have meant (kgs) pressure not load, I understand the mechanics envolved.
And there is a small surface area of the ends of the SFN
Which is why damage ocurrs. Or is that ten kgs load, not ten's...................I will give you that short of a calculation

[andrewjoseph]

http://www.rutlandcycling.com/103395/pr ... JVXaPD_BwE

Sfn setter.

I don't like them, preferring hope head doctors.

[mig]

funny one really this. the SFN is 2mm down the steerer (above the stem if anything.) the spacers are sufficiently proud of the top of the steerer tube. the top cap nips up okay as does the stem but they leave forward and backward play in the upper bearing race of 2-3mm if pushed against an applied front brake. never seen the like of that before!

[531colin]

2 to 3 mm is an awful lot of play .....it sounds like wrongly assembled, rather than poorly adjusted to me.
If there is play only in the top bearing and none in the bottom bearing, is the wedge in place in the top (adjusting) cup?
Are the balls properly seated in the top race?

[mig]

i was coming to the conclusion that it is the balls in the upper race. will have to strip it next weekend i think.

is there no better way to perform the task done by an SFN? it does seem odd do a job by building in a small flaw in a component.

[NATURAL ANKLING]

Hi,
Hearing the click or knock when stationary rocking on the front brake or even visable, but 2 - 3mm.....sounds wrong parts / assembly.

[RickH]

is there no better way to perform the task done by an SFN? it does seem odd do a job by building in a small flaw in a component.

I have one of these (or an earlier but functionally similar model) on my road bike - it does have a carbon steerer which precludes a SFN but I prefer this type of fixing anyway & would probably use one, given the choice, on a metal steerer.



Rick.

[andrewjoseph]

i was coming to the conclusion that it is the balls in the upper race. will have to strip it next weekend i think.

is there no better way to perform the task done by an SFN? it does seem odd do a job by building in a small flaw in a component.

As I mentioned earlier, I use a hope head doctor in all our bikes. None have carbon steerer. Easier to get out and re-use.

[Valbrona]

Is the fixing bolt threaded along the whole of its length? If it is plain/unthreaded at the top you could be running out of threads as you tighten up. Setting the SFN lower will sort this.