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I recently bought a used suspension fork, and only at home noticed that the steerer tube is slitted. It is straight, as i would expect for an a-head, and not threaded, But it has a slit much like the seat tube in a bicycle frame. (The part where the clamp goes)

Can i safely insert a star nut and use an a-head, or do i need something else?

slitted steerer tube

Edit: I found a thingy called "speedlifter". The slit and hole look as if they would match that thing, if that is any help.

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  • How long is your head tube? Could be the slot ends up above?
    – Criggie
    May 7, 2023 at 19:17
  • @Criggie the slot is above the head tube, but the steerer tube is not long enough to cut under the slot.
    – Burki
    May 8, 2023 at 6:12
  • What is the brand/model of the fork?
    – olliebulle
    May 8, 2023 at 23:13
  • @olliebulle it's an sr suntour ncx lite mg
    – Burki
    May 9, 2023 at 5:45
  • What's an "a-head"?
    – Paul H
    May 9, 2023 at 18:52

2 Answers 2

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Short answer. No

The star nut isn't the primary issue. It exists to vertically preload the bearing stack until you clamp the stem bolts on the steerer. A stem clamps onto the steerer and stays there because the friction between stem and steerer is high when clamped.

With the slot in the steerer the steerer can compress under clamping forces and hence you wouldn’t get sufficient friction to guarantee that the stem would stay in place. Hit a big bump and the stem might pop off the end of the steerer leading to much sadness.

A possible hack is to make an inner shim tube with the same outer diameter as the inside of the steerer if you are dead set on the fork.

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Indeed, it seems like you have a Speedlifter ready fork. This mechanism enables the user to quickly adjust the handlebar height with a quick-release lever.

The slot is made with the help of one of their two tools:

Profil-Cut Tool:

enter image description here

Simple-Draw Tool:

enter image description here

In their Assembly and operator's manual on page 17, they specifically say to remove the star nut before adapting the fork.

If the steerer tube is not long enough to cut it or you are not able to put a star nut below the slot, then another option is to buy yourself a Speedlifter!

EDIT:

If you can cut the tube, but can't cut it below the slot, according to Park Tool, the star nut should be about 15 mm (9/16″) below the top of the steering column. FWIW that is where their TNS-1 tool puts it. Ideally this way, you would also be able to attach your stem below the slotted part of the steerer tube.

enter image description here

This setup would seem reasonable, but even then, I can't guarantee anything as the fork has been modified in a way that is not intended by the manufacturer.

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  • Thank you. Yet, my question remains: assuming i can get a star nut below the slot, can i safely use an a-head stem with this fork? And if i need to cut it, but cannot cut it below the slot, how much "un-slotted" material do i need to safely use an a-head stem?
    – Burki
    May 9, 2023 at 12:03
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    At the very end of the cited manual, it states: "If the Speedlifter is to be permanently removed from the head tube of the fork, the A-Head® stem cannot simply be reinstalled on the slotted shaft. First, an A-Head® star nut must be inserted in the shaft (approx. 50 mm from its upper edge). The Speedlifter reinstallation shim must then be installed in the slotted portion of the fork shaft. The A-Head® top cap can now be fastened, but only with an extra long M6 Allen bolt. For more details contact your dealer."
    – Jahaziel
    May 10, 2023 at 16:49
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    I searched the website for this "reinstallation shim", but had no luck. I sounds to me that this shim is the concept that Warren Burton mentions in their answer.
    – Jahaziel
    May 10, 2023 at 17:00
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    @Jahaziel great find. I completely overlooked that part of the manual.
    – olliebulle
    May 10, 2023 at 23:52

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