This time we’ll look at how to identify and adjust a “threadless head set”. Let’s take a look at an example…….
Threadless head sets are pretty common these days.
The “threadless head set” gets its name from the fact that the steer tube of the fork is not threaded. This type of head set has been in wide circulation since the mid-90’s and is almost all you see on modern day bicycles. The stem on a threadless head set system clamps around the steer tube and is responsible for holding the head set adjustment. The “top cap”, which is over the top of the steer tube, has a bolt running through its center that threads into an “anchor” lodged in the steer tube called a “star nut”. These are the principal parts involved in our discussion of adjusting this sort of head set.
Most threadless head sets have stems clamped at the top of the fork steer tube.
Alternate loosening bolts on threadless stems to reduce the chance of overstressing the clamp and possibly causing cracks to develope on the stem.
The first order of business is to release the stems grip on the steer tube. This is done by loosening the bolt(s) that are clamping the stem to the steer tube. Note: If there is more than one bolt holding the stem to the steer tube, it is best to release the bolts as evenly as possible to reduce unwanted strain on the stem. Turn each stem bolt alternately with turns of less than half a full turn at first until the stem is quite loose. The stem is loose enough when you can turn it on the steer tube and the wheel stays stationary.
The only thing this bolt does is adjust the preload on the head set bearings
Next we’ll tackle the actual head set adjustment. Turn the bolt in the center of the top cap, (usually a 5mm bolt) clockwise about an eighth of a turn or less. Re-tighten the stem bolts, again using alternate turns on bolts if there is more than one bolt, and then check your adjustment. Just as with a threaded head set, you want to try to rock the fork back and forth in the head tube by grabbing one of your grips and the front wheel. If you still feel a knock, or some looseness, try the adjustment procedure again until you get a satisfactory result. Remember! Small adjustments, not big ones, and it may take a few tries.
Once you get what you think is a good adjustment, make sure you have your stem lined up straight with your wheel, and double check those stem bolts that clamp the steer tube. Don’t try tigtening that stem cap bolt! All it is there for is to make adjustments. Note: Some higher end stems and steer tubes require specific torque values to be met for safe riding. Over tightening some exotic carbon steer tubes or aluminum/carbon stems can result in failures. Use a torque wrench, or see your local bike shop for assistance if you are not comfortable doing this adjustment on your higher end machine.
Many stems will have torque specs listed right on them, others will require some research. If you have a higher end machine, follow the torque specs carefully!
If you just can’t seem to get your head set to adjust up, here are a couple things to check. First- See if the star nut is slipping or damaged. To do this, simply back out the center bolt in the top cap and remove the top cap. The star nut should be solidly wedged into the steer tube and not crooked, or with stripped threads in the center. If the star nut is damaged, a new one will have to be pressed in before you can continue. See your local bike shop for assistance. If the star nut checks out, look at the steer tube in relation to the top of the stem. Are they equal in height? If so, their isn’t enough spacers under the stem. You should be seeing at least a 16th to a 1/8th inch difference between the top of the stem and the steer tube, which should be lower. If you need assistance, see your local bike shop for parts and help. You won’t be able to adjust the head set properly until the problem with the spacers is addressed.
Next time: Adjusting the rear derailleur