What danger a star spangled nut in a carbon steerer?

jumbojimbo

I took my road bike in for a service but the mechanic phoned me later the same day refusing to do it because it had a star fangled nut, and not a compression plug, fitted to the carbon steerer. He said it was potentially dangerous, but is it?

I don't want to damage the forks trying to extract the star fangled nut, and I can't afford to replace them at the moment if I did, but at the same time I don't want to be going downhill at 40mph with the thought, however slim, that the steerer could fail!

Any advice?

Hermes3000

I understand that the compression plug, which is normally used reinforces the steerer, prevents the stem from crushing it. The star-fangled nut may also compromise the integrity of the steerer during insertion.
Forks are cheap compared to the potential dentist's bill.

tri-sexual

Cannondale?

Monty Dog

Some manufacturers e.g. Cannondale are reknown for persisting with star-fangled nuts in carbon steerers whilst everyone else steers clear. FWIW you'll probably do more damage to the fork in trying to remove it. There is a perceived risk that the installation of the nut scratches the inside of the steerer and therefore creates stress-raisers which could ultimately lead to failure at some point in the future. I'm not sure there's ever been a recorded incident of steerer failure due to a star nut - the vast majority are due to crushing due to over-tightening the stem clamp. Taking a pragmatic view I'd just leave it be and wouldn't bother going back to Chicken-Licken the mechanic either!

Velonutter

Using a star nut in Carbon forks is dangerous, it will slip and never lock up.

You should always use am expansion plug with carbon forks, no exceptions.

balthazar

Velonutter wrote:

Using a star nut in Carbon forks is dangerous, it will slip and never lock up.

You should always use am expansion plug with carbon forks, no exceptions.

?? I've encountered star nuts in carbon steerers before, that were fixed solidly enough to preload the headset — their only function. On inspection I didn't see damage to the inside of the tube that would be cause for concern.

I agree completely with Monty: I'd use a plug by choice, but changing now would only make things worse, and there's no need for scaremongering.

Velonutter

@balthazar

Not scaremongering at all, when you come down a fast hill and notice your headset has come loose from the bump you have just gone over and all because you didn't use the proper fitment, then it will probably be a bit late!

Changing will not make things worse because a star nut is easy to knock out as there is no friction to stop it, it's only with Aluminium Steerers that a star nut takes a bit of fettling!

balthazar

Velonutter wrote:

@balthazar

Not scaremongering at all, when you come down a fast hill and notice your headset has come loose from the bump you have just gone over and all because you didn't use the proper fitment, then it will probably be a bit late!

i think you have a miscomprehension about the function of this fixing. It doesn't attach anything— it's only used to fine-tune the headset preload. After tightening the stem bolts, you could remove the top cap, bolt, and expansion plug completely without consequence (apart from making subsequent adjustment difficult!).

The top cap assembly is best thought of as an instrument that's carried on the bike for future convenience.

sheffsimon

Velonutter wrote:

@balthazar

Not scaremongering at all, when you come down a fast hill and notice your headset has come loose from the bump you have just gone over and all because you didn't use the proper fitment, then it will probably be a bit late!

Changing will not make things worse because a star nut is easy to knock out as there is no friction to stop it, it's only with Aluminium Steerers that a star nut takes a bit of fettling!

Star nut doesnt hold the stem on so why would the headset come loose because of it?

I would leave it TBH, is there any record anywhere of a carbon steerer snapping because it had a star nut in it, particularly since the nut is digging into the steerer well above where the bending forces applied by the stem are highest?

Velonutter

No mis-comprehension, with the recommended load recommended by my stem 5nm it ain't a great deal, with Aluminium it is different as you can crank up the bolts but Carbon is a different ball game.

Your choice, I wouldn't and you would, I'd rather be extra safe and do things properly. :roll:

Velonutter

SheffSimon wrote:

Star nut doesnt hold the stem on so why would the headset come loose because of it?

I would leave it TBH, is there any record anywhere of a carbon steerer snapping because it had a star nut in it, particularly since the nut is digging into the steerer well above where the bending forces applied by the stem are highest?

But that is precisely the problem, the star nut can't dig into carbon like it does with Aluminum and therefore can't grip

Who ever said that a Carbon Steerer would snap, I didn't, it won't but it will slip with a Star nut and that is the issue.

Look for the sake of a tenner which would you rather have, peace of mind or a broken body!

balthazar

Velonutter wrote:

SheffSimon wrote:

Look for the sake of a tenner which would you rather have, peace of mind or a broken body!

I don't mean to labour this- but that's beside the point. It's about an accurate description of the scenario, and diagnosis of the problem. Monty's initial comment was precisely that.

It's meaningless to use torque loads on a preload instrument. "cranking up the bolts" would lead to an immobile headset. It may be true to say that the fixing encounters loads of approximately 5Nm, but that isn't how you set bearing preload. I still think you don't quite understand this interface if you think it has consequences for safety.

Velonutter

balthazar wrote:

Velonutter wrote:

SheffSimon wrote:

Look for the sake of a tenner which would you rather have, peace of mind or a broken body!

I don't mean to labour this- but that's beside the point. It's about an accurate description of the scenario, and diagnosis of the problem. Monty's initial comment was precisely that.

It's meaningless to use torque loads on a preload instrument. "cranking up the bolts" would lead to an immobile headset. It may be true to say that the fixing encounters loads of approximately 5Nm, but that isn't how you set bearing preload. I still think you don't quite understand this interface if you think it has consequences for safety.

Lets agree to differ Mate, I don't think you comprehend the dangers or the simple mechanics and you don't think I do, so lets draw a line under that and agree to differ.

springtide9

balthazar wrote:

i think you have a miscomprehension about the function of this fixing. It doesn't attach anything— it's only used to fine-tune the headset preload. After tightening the stem bolts, you could remove the top cap, bolt, and expansion plug completely without consequence (apart from making subsequent adjustment difficult!).

The top cap assembly is best thought of as an instrument that's carried on the bike for future convenience.

+1
The star nut / top cap are used to just used for adjusting the headset only. They serve no other function at all and are not designed for any load. That's the whole point about the design! It's the stem clamp that does all of the work on holding your forks on!
The reason for applying a little tension on the top cap nut (or giving a torque value).. is to stop it undoing and coming loose... and so that people don't put any proper tension on it... as it's not designed to take any load!

I wouldn't by preference use a star nut at all.... but they are a real bugger to get out if you need too - even of a pair of MTB suspension forks (where you can be a bit rougher)

I personally would be tempted to leave it in. I think you are more likely to cause damage to the carbon forks in removing it. Star nuts will go in with little scoring to the carbon (due to the design)... and are much more likely to cause scoring if you try and remove them.

Pseudonym

Velonutter wrote:

I don't think you comprehend the dangers or the simple mechanics and you don't think I do, so lets draw a line under that and agree to differ.

the 'simple mechanics' are that you appear to have misunderstood what keeps a headset under tension, once the cap bolt has been nipped up......

andyrr

Who put the thing in the fork to begin with ?
As mentioned, I've konly heard of Cannondales using these on carbon steerers - the walls are sufficiently thick I think.
I've seen some comments indicating that the presence of the compression plug inside the steerer where the stem is clamped helps to prevent the tightened stem from being squashed although others say that once the compression plug is used for removing the initial play from the headset they can be removed so you takes your pick ...
I'm sure the nut could be removed safely if you wanted to - maybe with a drill to break through bits of it so it just falls to pieces.

springtide9

andyrr wrote:

Who put the thing in the fork to begin with ?
As mentioned, I've konly heard of Cannondales using these on carbon steerers - the walls are sufficiently thick I think.
I've seen some comments indicating that the presence of the compression plug inside the steerer where the stem is clamped helps to prevent the tightened stem from being squashed although others say that once the compression plug is used for removing the initial play from the headset they can be removed so you takes your pick ...
I'm sure the nut could be removed safely if you wanted to - maybe with a drill to break through bits of it so it just falls to pieces.

The bung is not there to help prevent compression damage. It's only purpose is for adjusting the headset. The reason why bungs are preferable is so that they don't 'scratch' the carbon and potentially create a weakness if the scoring is deep. They are also much easier to remove without causing damage.

I have tried several times removing star nuts. Some have been successful; others unsuccessful. If someone here knows a 'tried and tested' way of removing them... please share.
I have tried the drill trick.... drilling through the centre so that you collapse the nut. Unfortunately the steel used seemed very tough when I tried (and there is no going back once you trash the threads). On one occasion... while drilling (with decent drill bits)... I had to put a reasonable amount of force onto the drill to get it to cut properly... and once the shell weakened a little... even trying to take care.. I pushed the bung further in... (which is where it then stayed!)
The drill method has worked for me on another occasion..... but I still ended up using more force than I would have liked. On both occasions they were on MTB suspension forks.
Personally after having a few attempts at this over the years... I'd live with it as they are. If you are that paranoid about it... treat yourself to an upgraded pair of forks. Most of the force on the bung probably has already been applied when seating the headset.. so it's unlikely the bung is going to cause anymore damage (unless you decide to remove it!)

PhilofCas

Velonutter wrote:

balthazar wrote:

Velonutter wrote:

SheffSimon wrote:

Lets agree to differ Mate, I don't think you comprehend the dangers or the simple mechanics

He totally does, that's why he's confident that his handlebars won't come off the stem if he pulls up hard, you're not understanding what is keep the fork/stem/handlebar safe and secure.

Spend a few minutes sussing it out and you'll see what everyone is saying....

A friendly mediator.

RowCycle

I've got a star nut in a carbon steerer, have done for a year or so, no problems so far...

LangerDan

springtide9 wrote:

andyrr wrote:

Who put the thing in the fork to begin with ?
As mentioned, I've konly heard of Cannondales using these on carbon steerers - the walls are sufficiently thick I think.
I've seen some comments indicating that the presence of the compression plug inside the steerer where the stem is clamped helps to prevent the tightened stem from being squashed although others say that once the compression plug is used for removing the initial play from the headset they can be removed so you takes your pick ...
I'm sure the nut could be removed safely if you wanted to - maybe with a drill to break through bits of it so it just falls to pieces.

The bung is not there to help prevent compression damage. It's only purpose is for adjusting the headset.

The bung does have a function in resisting compression forces. On Time frames using the "Quickset" head-set, all the bearing preload is applied using the headset topcap (not the stem cap) and the stem sits above this. There is no bung or star-fangled nut used in the steerer. Because of this, Time provides what they call a "compression stopper" to be inserted into the top of the steerer to protect against the forces from tightening the stem.

springtide9

LangerDan wrote:

springtide9 wrote:

andyrr wrote:

Who put the thing in the fork to begin with ?
As mentioned, I've konly heard of Cannondales using these on carbon steerers - the walls are sufficiently thick I think.
I've seen some comments indicating that the presence of the compression plug inside the steerer where the stem is clamped helps to prevent the tightened stem from being squashed although others say that once the compression plug is used for removing the initial play from the headset they can be removed so you takes your pick ...
I'm sure the nut could be removed safely if you wanted to - maybe with a drill to break through bits of it so it just falls to pieces.

The bung is not there to help prevent compression damage. It's only purpose is for adjusting the headset.

The bung does have a function in resisting compression forces. On Time frames using the "Quickset" head-set, all the bearing preload is applied using the headset topcap (not the stem cap) and the stem sits above this. There is no bung or star-fangled nut used in the steerer. Because of this, Time provides what they call a "compression stopper" to be inserted into the top of the steerer to protect against the forces from tightening the stem.

Does this mean we should also start fitting bungs into our carbon seatposts? Or doesn't it matter on the post where you have most of your body weight?

Time might be using them as a way to shave off more weight from their fork/stem combo - ans this is not the norm.

buder

balthazar wrote:

Velonutter wrote:

@balthazar

Not scaremongering at all, when you come down a fast hill and notice your headset has come loose from the bump you have just gone over and all because you didn't use the proper fitment, then it will probably be a bit late!

i think you have a miscomprehension about the function of this fixing. It doesn't attach anything— it's only used to fine-tune the headset preload. After tightening the stem bolts, you could remove the top cap, bolt, and expansion plug completely without consequence (apart from making subsequent adjustment difficult!).

The top cap assembly is best thought of as an instrument that's carried on the bike for future convenience.

+1 its the stem that locks everything in place not the startnut

Monty had it above, starnuts can dig into the steerer which is not a good thing in the case of carbon however.

The analogy above is not correct, the starnut itself just by it being there wont cause the forks to fail going over a bump down a hill at 40mph !!, I think what might be inferred is that the star nut could have caused existing damage during the pre-load stage which may contribute to a failure at some point if it has caused some damage to the inside of the steerer when the headset was adjusted.

More to the point which may help answer your question regardless of what you have in there at the moment how does the inside of the steerer look did the mechanic say ??.

You can get a bung for next to nothing if the forks are fine no need to change them but id want to know if it was mine if the starnut has caused any damage or not

rozzer32

I got some new 3T forks for my Cervelo and they supplied a star nut to use. But they also supplied an Aluminium insert that you have to bond to the inside of the carbon steerer where the star nut will sit. That says something to me that they don't want you to use a star nut with just the carbon. Does ask the question why they don't just supply an expander though :?

D4RK1

Am i missing a trick here? Im from a mtb backgroud and star nuts are as easy to remove as they are to fit. Just knock it all the way down the steerer and out the bottom. No need to drill and its not going to make anymore of a mess on the lower half of the steerer than the top half its already gone down.

Mark

keef66

That's what I was thinking. Surely the shape of the thing dictates it goes downwards a lot easier than it goes upwards? If it came upwards easily it would be pretty useless at it's job, no?

I'd just whack it further down to allow room to fit a bung. If the manufacturer saw fit to install one from new I can't see it doing irreparable damage to the steerer.

Cleat Eastwood

sorry if this is s tupid question, but whats the point of the nut anyway, and why cant you just clamp the stem to the steerer.

balthazar

Cleat Eastwood wrote:

sorry if this is s tupid question, but whats the point of the nut anyway, and why cant you just clamp the stem to the steerer.

It's to apply finely controlled preload to the headset bearings. It's possible to do everything up without (I have done before, in a pinch), but bearing adjustment will be considerably off. With needle roller bearings, which some headsets have, precise adjustment is even more critical for long life.