Another slipping expander plug, what torque on the preload you need to sieze the headset?

[musiclover]

Extra cautious people like to fix their handlebar first, than drop the expander inside, expand it to the recommended setting, then loosen the stem bolts, assemble the handlebar in normal order. (In order to prevent the expander of expanding the fork out too much without the stem protecting it from the outside).

This is what I have done the last time I dealt with it, but for some reason when I went ahead today to clean my headset the expander was 1 mm out of the fork.

I want to drop it fully this time, torque up to the recommended setting without any stem outside the frame, and then fix it as per normal.

1. Do you think it is safe to expand the expander to 8 nm with fork outside the frame (without stem tightened around the fork)?
2. Why do you think my expander could have been a bit out?

[DaveS]

Whether it's safe to install an expander without the stem in place depends on it's design. Some are not very long and could damage a steering tube. The smart thing is to not do that.

Your plug was above the top of the steering tube because it slipped. That suggests a problem with it.

I avoid expanding plugs entirely. I glue in a M6 thread insert and fill most or all of the stem clamp area with solid epoxy. Most often I use a star nut with the OD ground smaller so it just slides into the tube. A 1 inch star nut only needs a small reduction in diameter. My frames are usually slammed, so the steerer can't be cut any shorter. My current frames could have 10-15mm cut off, so I just set the star nuts deeper.

[Cleaner]

No, it is not adviseable to expand the plug without the stem and spacers on the outer wall of the steerer tube. The hoop stress induced by the expander will be higher without the compressive stress of the stem being clamped on the outside. You run the risk of exceeding the stress limit of the steerer tube material. You can torque it lightly (1-2 Nm) without issue but torqueing it up to spec is potentially problematic.

Many drop in expanders are designed to expand radially within the clamped area of the stem. They are designed to work in conjunction with the stem clamp forces acting in opposition to the exapnsion forces.

If your exapnder is migrating upward during use then something is amiss. It likely slipped within the tube. Without seeing it, it is hard to tell what the root cause would be. Make sure the top cap is no hitting the top of the steerer tube before bottoming out on a spacer or the stem. Do not over tighten the stemp cap bolt as that will act to pull the expander out the top. Only tighten it enough to take the gap out of the stack to seat the bearing races and then another 1/8 to 1/4 of a turn.

Also measure to insure that the expander is vertically aligned with the stem collar if it is designed to be there.

[Orlok]

Extra cautious people like to fix their handlebar first, than drop the expander inside, expand it to the recommended setting, then loosen the stem bolts, assemble the handlebar in normal order. (In order to prevent the expander of expanding the fork out too much without the stem protecting it from the outside).

This is what I have done the last time I dealt with it, but for some reason when I went ahead today to clean my headset the expander was 1 mm out of the fork.

I want to drop it fully this time, torque up to the recommended setting without any stem outside the frame, and then fix it as per normal.

1. Do you think it is safe to expand the expander to 8 nm with fork outside the frame (without stem tightened around the fork)?
2. Why do you think my expander could have been a bit out?

1. You must be crazy to think so.!
2. Not fixed the expander to the recommended setting before fixing the handlebar with the topcap, in that case when you tight the topcap you'll be force the expander out of the steerer tube.!

[tommyboyo]

Yes, it is absolutely fine.

Done it on many tarmac's down the years.

In fact, never done it the other way.

[ghostinthemachine]

Depends on the steerer. And the safety factor.

Have seen some split even when doing it almost properly.

[MikeD]

You should do up the expander first, then tighten the stem bolts. An expander helps keep from crushing the steerer tube when the stem bolts are tightened. If you have the expander in there without it being tightened up, it's just like not having one in there and isn't providing any support.

[BigCol]

It's fine!

See video below from enve - tightening to 8nm with no stem in place

https://support.enve.com/hc/en-us/artic ... structions

[spartacus]

Y'all need to stop blindly tightening things to spec. I don't think most expanders need to be at the maximum safe level to stay put.

[musiclover]

It's fine!

See video below from enve - tightening to 8nm with no stem in place

https://support.enve.com/hc/en-us/artic ... structions

Yes, I have seen that video as well before I asked the question. I think it will be naive to think that 8Nm could damage a carbon fork from within without the stem protecting it from outside.

Y'all need to stop blindly tightening things to spec. I don't think most expanders need to be at the maximum safe level to stay put.

How do you need to do it then without "blindly following the specs"? Use the minimum force and hope it will not slide out?

[musiclover]

Ok, so it's been confirmed, I have an expander with really slippery and smooth body and it does slide out (when torqued to recommended torque). How can you keep it in place other than an epoxy glue?

PS it does not slide out only when I am using minimal force at the preload bolt at the stem... But then I have never been able to use enough force for the preload bolt to slow the steering down.

PPS However, I have to say that the torque I use in attempt to "overload the preload" is quite significant.

[Nezz0r]

Not so sure about a torque rating for an expander anyway. Exception of course for a manufacturer supplied expander installed per manufacturers specifications (location in steerer and relative to stem).

I do them up enough to maintain position, install stem and then put more load on the expander. I use non manufacturered expanders (with a metal sleeve to distribute forces) and do not torque it to a specific number.

Of course I forgot to read all posts and my point was already made. Attached a pic of my expander sleeve (good friction-rich material).

Edit2; I do up the stem after tightening expander.

[musiclover]

Ok, at this point it is not clear what the problem was and what I am trying to achieve, I will give a quick summary and maybe someone will be able to help.

When servicing my headset I noticed: that there was some damage on the bearing cups (places where headset bearings sit in the frame) and that the expander slipped up 1 mm.

I have been told that in order to prevent further damage to the carbon cups where the bearings are I need to tighten the stem preload bolt a bit more, but there seem to be a problem with that as the expander slides up.

I tried to clean the inside of the steerer tube with isoprpyl, torque the expander up - it would always slide up when I would try to torque the stem bolt to the point where the preload forces start getting in the way of the headset bearings free rotation (not able to create enough preload to prevent handlebar dropping to a side under gravity). So, I have never been able to achieve that on this bike yet.

I have then tried to use an old tube on top of the expander to create more friction - it did not work as the expander will not fit inside the fork with tube on top.

I then used some Loctite 243 on the expander but then found out that a) it will not cure if it is not metal to metal b) it may damage the carbon so I removed it.

Unfortunately, I do not have carbon assembly paste so not able to try that.

At the moment I have used some b7000 adhesive as it seems to be very gente to plastics, but it's adhesion normally is not strong at all, so I doubt it will make any difference.

I would use some epoxy adhesive to lock the expander in the steerer forever since it is already slammed anyway. But I just might want to take it out in the future and besides I do not know for sure that there is enough gap between the top of the expander (it goes on top of the steerer tube)...

So, what would you recommend? Am I missing something? Thanks

[Cleaner]

Are you positive that the top cap is not bottoming out on the top of the steerer tube when torquing the screw? That will pull the expander up inside the tube if it is.

If you are unable to preload the bearings in the headtube to eliminate play then something is out of spec with the parts. You should approach this methodically to determine what the issue is. If you can not determine the root cause I would consult with an experienced mechanic to help you. There are multiple items that could be cause of the issue and it is very difficult to diagnose over the internet.

I would not advise application of any permanent bonding agents to the exapnder unless you are using a system thay is designed to be bonded into a steerer tube.

To test the bearing preload, assemble everything to spec. You can then apply the front brake only and push the handlebars to the front, if there is bearing play in the head tube then you will percive this disaplacement. You essentaill rock the back forward and aft and feel/listen for any movement in the stack up. The objective to is take out all of the slack and tighten the top cap bolt a fraction of a turn more. Check this ofter each ride to make sure it is holding.

One easy thing to test is trying a differrent expander. It is possible that the expander is too small radially when expanded or the steerer tube has had material removed by the expander slipping which has made the nominal gap too big for the expander to function to spec. If you suspect this then wrap a single layer of thin cloth tape around the expander to see if that make a difference. This is not a solution but can help determine the root cause. If the tape shows an improvement then that suggests the expander is undersized and is not generating sufficient normal force on the ID of the steerer tube/

If that does not make a difference then you need to methodically go through all components in the stack up to eliminate them as the cause. keep in mind that it may be a combination of parts that is an issue and not one single component.

[musiclover]

At first I thought that maybe that 2.5MM gap between the top of the expander and the top edge of the stem was not enough.

That is why to troubleshoot that I have put a spacer at the top... It has not changed a lot.

Also, if the system was bottomed out, I do not think the expander will have a lot of space to raise up high.

No there is no play in the system. Until I hit a bump on the road (I think) judging by the sounds and damage of the cups. I have not been able to confirm positively there is any play at all, just saying regardless of the top cap preload force the steering is still smooth and very light.