Head Tube Basics - Page 1 of 3
Figure 1 - Head tube, front fork and hardware
This section will cover some of the basics you need to know when pulling apart the steering system of a bicycle for repair or use on one of your own custom designs. A bicycle steering system is lightweight, robust, and highly efficient, and like many mechanical devices, there are several "standard" sizes that are not interchangeable. Knowing how a bicycle steering system is put together will make it much easier to salvage the parts needed for a more complex steering system such as the one used on a tadpole trike or quadcycle.
Most of the head tube hardware will be the same on the bicycles you pull apart with the exception of the length of the head tube and the difference between the two commonly available fork stem diameters. This article will refer to the actual hardware that allows the front forks to move smoothly back and forth such as the bearings, cups, and races. Figure 1 shows a complete front steering assembly cut from an old bicycle frame. I often keep these parts together as a matched set, although most can be interchanged, as long as the fork stem length matches the head tube length.
Figure 2 - Removal of the lock nut
To remove a fork from a head tube, you must first loosen the top locking nuts as shown in Figure 2. There are usually two nuts, a large top finished nut (the larger one) and a thin locking nut that helps the two lock together over the washer, which is still shown on the fork stem. All fork hardware is unscrewed in the counter clock wise direction, since these are standard threads. A large adjustable wrench or a pipe wrench can be used on most of the fork hardware, although the pipe wrench should not be necessary unless the threads have rusted significantly.
Figure 3 - The washer fits on the slotted stem
Notice that the washer, which fits under the lock nut has a key that fits into the slotted section of the fork stem. The purpose of this slot is to prevent the washer from turning along with the locking nut when you tighten it. If the washer is allowed to turn, it would also force the adjustable race to turn and become overly tight over the bearings.
Figure 4 - Removal of the adjustable bearing race
The largest nut in the head set hardware is the adjustable bearing race shown removed in Figure 4. This part creates a bearing surface between the head tube cup to allow the forks to turn with minimal friction, yet remain securely in place. Take note of the orientation of the bearings when you disassemble the head set as it does matter which way they are put into the cups. As you can see in Figure 4, this type of bearing includes a ball retainer and fits into the cups so that the balls face the cup. Sometimes bearings simply fall right out, so in that case you just pack them all back in when reassembling the head tube hardware. A cracked or badly rusted bearing or race needs to be replaced.
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