Headsets: Shimming a Loose Race or Cup

 

 Occasionally you come across a project where the crown race will not tighten firmly down onto the the top of the fork crown. 

There are three common way to remedy a loose fork crown:

• Shim the steerer tube area where the crown race goes to tighten the fit.
• Use Loctite or similar products to fix the crown race in place.
• Replace the fork or crown race with another that fits tighter.

My preference is to shim. The reason for this is it allows you to use your original fork and your original, good crown race. Here's how I do it - let's use this loose Schwinn Racer crown race as an example.

 Take a piece of thin, pliable sheet metal. I have a sheet of thin brass that I use for this task. I have owned the sheet for many years and it has come in handy many times on many projects. I trim a strip of metal that is a bit wider than the area where the crown race goes. Then I wrap the steerer tube with the shim and slide the crown race down. Keep your wrap as flat and even as possible around the tube.

Above thin sheet brass. Aluminum can also be used.

 

Fitting is done by feel. The crown race should be tight enough that you have to tap it into place gently. It should not be loose, but it also should not be so tight that you have to bash it into place. To tap the race into place, I use a mallet and hardwood dowel. A punch can be used if you carefully tap around the edge of the race and not where the bearings run. A wooden dowel gives you a little more flexibility in tapping on the race. 

Tap around the edge evenly. You should see the race lowering into place gradually. Keep tapping until the race is snugly in place. You should not be able to turn the crown race in place with your bare hand. 

 

Above: crown race with shim, next is to cut off the excess brass

 

Next, carefully run the blade of a utility knife or tip of a file around the shim where it sticks out above the crown race. This is to remove the excess shim.  Be careful when cutting and removing the excess shim- the knife and the shim material are sharp. Take your time and don't cut too deeply.

In a pinch, you may be able to use a strip of aluminum, such as you'd find with a soda can or a beer can. I prefer brass, but any malleable, thin metal shim is better than a loose crown race.

I've also seen Loctite used for this job. Loctite works OK so long as the crown race is only slightly loose. Loctite is not great at filling larger gaps. I like the brass shim because the soft metal conforms to the shape you need.

 

 Works for Cups Too...

Similarly, headset cups can be shimmed in the head tube the same way: by cutting a thin metal strip, shaping into a ring, and then tapping in the headset cup. Again, it should be snug enough that you can't turn the cup in place by hand. Be careful though that it is not so tight that you deform the cup or crack the frame. A flashlight is helpful to see into the head tube to make sure your shim is properly wrapped.