Hi everyone, I have top cap that came with a locking star mechanism. It looks like it is a bit wide to fit into the stem. How do I push the star into the stem? Rubber mallet?

yes use a rubber mallet and drive it down 15 mm from the top . keep it straight as you do. parktool makes a tool (Item # TNS-1) that make it easier .

First if you have a carbon steerer tube you MUST NOT use a starnut, you must use an expansion plug. If you have a steel or Aluminum steerer and the proper starnut proceed as below.

Get a long bolt, say 60 or 75 mm, with the correct threads (usually M6 x 1.0) and thread the starnut onto it so the fingers point toward the bolt head and the threads are completely within the nut. Then center the nut over the steerer with the bolt on top. Use a hammer on the bolt head to drive the nut down until it's flush or just below flush with the top of the steerer. Use care to drive in in parallel to the center line of the steerer. Once it's flush, remove the bolt, place the headset's top cap over the steerer and thread the bolt back in through the center hole of the top cap and through the nut. Drive the nut down until the top edge is about 15 mm below the top of the steerer using the top cap as a guide to keep it centered. Remove the bolt and install your spacers and stem. Fit the top cap and the provided bolt and adjust the headset.

Or use a tool designed for the job https://www.parktool.com/product/thre...t-setter-tns-1, make life a lot easier, and get's it installed correctly every time

i just did this for the first time myself and used a slightly different method that i read about here on the forum a while ago. not only did it work perfectly but i didn't have to go to the hardware store. (you need a socket wrench set though).

Here's what i did:

• put the allen bolt you have into the star nut (remove the top cap). screw it in not all the way, but maybe 1/3 or 1/2 way, enough that it's in there pretty well.
• from your socket set find a bit that fits over the top of the allen bolt but is smaller diameter than the star nut. I used maybe a 10mm wide "long" bit (the inner diameter of the bit should be as close to the outer diameter of the allen bolt as possible
• put in place and gently tap it in with a mallet to the correct depth
• it should be pretty easy to keep straight the taller the bit you have

Hopefully that makes sense, i usually bring them down to the bike shop but i gave it a shot this way and it worked perfectly.

In this picture you'd use one of the first couple as pictured (back row, right - narrow and tall)

I have used a socket wrench, works perfect and save me some money

As recommended above, the correct tool is the way to go if you are doing a lot of headset installations as in a bike shop or if you run a bike repair business. It's an extravagance for the home mechanic who may install a new fork and headset only a few times in a decade. Either the long bolt or deep socket methods work fine for occasional installations where time is not of the essence.

Note: No matter how you install the starnut do not stand the fork on it's dropouts while pounding it in.

I find it's an extravagence worth having, I only work on my own bikes, but it saves a lot of time when needed, & it's a cheaper tool as far as Park Tools go.

Piling on,+'s .. steel steerer tube is a must, I'd not like digging big scratches
in an aluminum steerer banging one in,
(edit) I note reading dealer catalogs,
there is a special star nut made just for aluminum steerers)

and carbon is a big Nyet. compression clamp/nut probably better..
for CF & Al.

Just to let you in on my experiences, the last time i installed one i was having a bad day. I used a socket as previously described with the bolt running up the centre of the socket to help keep the star nut square as it went in, but where i went wrong, i knocked the star nut in too deep and the bolt wasn't long enough to reach it. Then i thought i could knock it all the way through and out the bottom of the steerer but of course the steerer is butted and it wouldn't go all the way through.

I had to go get another star nut and the first one is still down in there, sometimes i'm such a dummass.

I prevent this by marking the shank of the bolt with a marker about 15 mm above the top cap and use that as a depth indicator. Drive the bolt and starnut down until the mark is even with the top cap.

+1000 on that.

If you drive one too deep again, before you pound it all the way down the tube out of the way, you can usually drill out the center enough for the petals to break off and get the pieces out.

KeS