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Used an Expander instead of Star Nut on Carbon Fiber fork.

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Used an Expander instead of Star Nut on Carbon Fiber fork.

Old 06-04-17, 11:04 AM
  #1  
Mark42
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Used an Expander instead of Star Nut on Carbon Fiber fork.

Couldn't get the darn star nut into a carbon fiber steerer tube. Try as I might, it would not go in because the wall of the CF tube are much thicker than a steel tube. Even after bending up the tabs on the star nut to give it a smaller diameter. Still no go. I found steerer tube expanders, and ordered one. Lubed up the cone surfaces with a touch of grease, and it installed and gripped tight.

I'm wondering how tight can I make it before possibly breaking the CF tube? How tight is tight enough to hold firm? Also, the headset is a cartridge style, and no matter how tight the cap screw gets, the bearings don't seem to notice and show no resistance to turning like what happens with cage bearings. Is that normal with cartridge headsets?
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Old 06-04-17, 11:15 AM
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Star nut will cut into the composite structure gouging thru the epoxy.

If you add an interior sleeve of metal , to protect the composite structurally..

then you might get away with a star-spangled nut ..

I cannot say if you irrevocably damaged the fork, trying....


Expanding one was what you should have used in the 1st place..


I / We, here, cannot say "how tight"?, unless you use a torque wrench,
then 'how tight' is communicating a standard unit of measure, number.





....

Last edited by fietsbob; 06-04-17 at 11:21 AM.
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Old 06-04-17, 11:35 AM
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I just disassembled a carbon steer tube expander/headset/bearings last night. I tightened mine just enough that it didn't slip while setting the headset preload. If it had slipped, I would have tightened slightly more, until it didn't slip. You only need the bearing preload tight enough that there isn't any play when holding the front brake and rocking the bike.
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Old 06-04-17, 12:10 PM
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Listen to Bob. No star nut in Plastic steering tube!
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Old 06-04-17, 12:17 PM
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Your not supposed to use a metal star nut in a carbon steerer.
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Old 06-04-17, 12:18 PM
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Originally Posted by Mark42 View Post
Couldn't get the darn star nut into a carbon fiber steerer tube...
Good, because you could've ruined your fork.

Originally Posted by Mark42 View Post
I'm wondering how tight can I make it before possibly breaking the CF tube? How tight is tight enough to hold firm?
It doesn't have to be all that tight -- just enough to resist the pull from the stem cap while you're adjusting the bearing preload. Once you've set the preload, then tighten the stem clamp bolts. It's the stem clamp bolts -- not the top cap bolt -- that bear all the load when you're done setting up the headset.

Originally Posted by Mark42 View Post
Also, the headset is a cartridge style, and no matter how tight the cap screw gets, the bearings don't seem to notice...
Off the top of my head, I can think of two possibilities:

(1) You've already tightened the stem clamp bolts. Those need to remain loose until you've set the bearing preload with the top cap. Then, once you've got the bearing preload adjusted (or rather, you've got the play removed), tighten the stem clamp bolts.

(2) The fork's steerer tube cannot reach all the way to the top of the stem (or spacers above the stem) while you're adjusting preload with the top cap. Otherwise, you're tightening the top cap down against the steerer tube and not the stem and spacers.

If you're unsure of what you're doing, there are plenty of good step-by-step tutorials like this one online.
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Old 06-04-17, 12:27 PM
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Originally Posted by Mark42 View Post
Couldn't get the darn star nut into a carbon fiber steerer tube. Try as I might, it would not go in because the wall of the CF tube are much thicker than a steel tube. Even after bending up the tabs on the star nut to give it a smaller diameter. Still no go. I found steerer tube expanders, and ordered one. Lubed up the cone surfaces with a touch of grease, and it installed and gripped tight.

I'm wondering how tight can I make it before possibly breaking the CF tube? How tight is tight enough to hold firm? Also, the headset is a cartridge style, and no matter how tight the cap screw gets, the bearings don't seem to notice and show no resistance to turning like what happens with cage bearings. Is that normal with cartridge headsets?
You really need to understand how to do this correctly, so that you don't damage your steerer.

Any install notes for carbon steerers tell you to never use a star nut.

You only need to tighten the expansion plug enough to hold it in place while setting the bearing preload, an easy to moderate tightening is all you need.

Bearing preload adjustment

See the Park Tool repair guide

The stem must be a few mm lower than the top of the stem or any spacer above the stem.
Like this example, showing an aluminum steerer.


This allows the cap's center bolt to pull up on the steerer tube, preloading the bearings. Like SkyDog75 said, the stem's two clamp bolts must be loose when you do this!

Tighten the cap with very light finger pressure, barely tightened. Then straddle the bike, hold the front brake, and rock it back and forth. You can feel the click/clunk when the bearings are still loose. Tighten just enough to make the movement go away.

Spacer above the stem
Many carbon steerer manufacturers recommend a spacer above the stem, to move the clamping force downward from the edge of the steerer.

Like this. The steerer tube extends above the stem, and needs a spacer that's a few mm taller, to keep the preload gap.




Stem clamping torque
You must be careful not to crush the steerer. Use just enough torque on the two bolts to keep the stem from moving. I hold the front wheel between my legs, facing the back of the bike, and try to turn the handlebars with an easy amount of force, to make sure the stem doesn't move.

If it's not quite tight enough, the bearings will get a little loose after a few rides. Just do the front brake-rocking the bike test again to see if everything is still correct. If it's gotten loose, you'll want to re-do the preload (undo the two bolts of course), and use a little more torque on the two bolts. Don't overdo it.

An example of a crushed steerer:

Last edited by rm -rf; 06-04-17 at 12:44 PM.
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Old 06-04-17, 12:44 PM
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Most expanders I have seen require no more than 7nm.
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Old 06-04-17, 01:25 PM
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Thanks for all the great input. I never had a carbon fork before and this one came with no instruction. Knowing how easy it is to get star nuts into steel steerers, I was not about to start hammering on this CF fork. I had no idea the espanders were available, but I just started browsing the parts sections of bike websites for steerer tubes and found them. Set the preload so rocking the bike didn't show any movement at the crown. Thats the way I left it. I am surprised at how strong the CF fork is seeing as it is so light.

Thanks again for all the advice. I really do appreciate the time it takes to post your knowledge.
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Old 06-04-17, 01:50 PM
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I could not find torque spec for my fork so I went with 8 Nm which is the spec for some ENVE forks.


-Tim-
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Old 06-04-17, 02:30 PM
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Originally Posted by Mark42 View Post
Thanks for all the great input. I never had a carbon fork before and this one came with no instruction. Knowing how easy it is to get star nuts into steel steerers, I was not about to start hammering on this CF fork. I had no idea the espanders were available, but I just started browsing the parts sections of bike websites for steerer tubes and found them. Set the preload so rocking the bike didn't show any movement at the crown. Thats the way I left it. I am surprised at how strong the CF fork is seeing as it is so light.

Thanks again for all the advice. I really do appreciate the time it takes to post your knowledge.
did you add a spacer to the stack? sounds like you NEEDED an extra spacer, from your earlier posts... the side load on the bearings WILL bind up the bearings, if there is enough free space at the top of the tube, inside the stem. I make sure there is about 1/8 to 1/4 inch inside the stem to allow adjustment... i try to use 1/8" as a minimum... some top caps require more, btw.
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Old 06-04-17, 02:53 PM
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Originally Posted by SkyDog75 View Post
It doesn't have to be all that tight -- just enough to resist the pull from the stem cap while you're adjusting the bearing preload. Once you've set the preload, then tighten the stem clamp bolts. It's the stem clamp bolts -- not the top cap bolt -- that bear all the load when you're done setting up the headset.
+1 Once you have set the preload and tightened the clamp bolts the top capand its bolt are no longer needed except to cover the hole.
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Old 06-04-17, 04:23 PM
  #13  
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Originally Posted by maddog34 View Post
did you add a spacer to the stack?
The steerer tube is about 4 mm or so below the cap.
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