A lot rides on your bicycle’s headset, and most modern bikes are equipped with the “threadless” variety. This rather intricate assembly allows the front wheel to swing smoothly from side to side, and when paired with a suitable stem, it also keeps the fork securely attached to the frame, a matter of no little interest to the thoughtful cyclist. Here’s an exploded view of a typical threadless headset, thanks to Keithonearth and Wikipedia:
The pictured headset uses cartridge bearings, but loose ball bearings in retainers are common, too. The upper and lower races are press-fitted into the bike’s head tube, and if they’re improperly bedded, or if the grease washes away and you don’t replace it, the result can be “indexed steering.” This is something you don’t want.
A properly adjusted, well-lubricated headset will permit the front wheel to swing smoothly and easily from side to side, with no noticeable wobble, or “play.” To check for excessive play, just lock the front brake while rocking your bike back and forth. If the headset is very loose, you’ll hear (and feel) a distinct clunk. This is a rather undemanding test, however. To catch the trouble before it reaches the clunking stage, just cup your hand around the fork crown and repeat the lock-and-rock process. Now you’ll be able to feel even the slightest click.
And what if you do elicit a click or a clunk? What then? Easy: Take up the slack. But don’t overdo it. Too much preload on the headset bearings will shorten their life. The aforementioned “indexed steering” is one likely result. It’s pretty easy to spot, though it’s a lagging indicator of headset trouble. By the time you notice it, the damage has been done. Still, it’s something you want to know. Just lift the front wheel off the ground and swing the bars from side to side. Smooth and easy? Then you’re good to go. But if the wheel moves from one apparently preset position to the next (that’s where the “indexed” comes in), you’re overdue for a new headset.
Fair warning: Swapping out a headset is not a job for the faint of heart. See “Further Reading” below for details. But here’s a worst-case scenario for your consideration: Farwell’s stock-build Surly Long Haul Trucker arrived with a poorly bedded headset. Unfortunately, it passed all the quick-and-dirty tests. The wheel turned easily, and there was no obvious indexing. It did seem a little hard to adjust the play, however. It was either too lose or too tight. But Farwell was in a hurry to get his new bike on the road, and he ignored the warning signs, settling for a “close enough” adjustment.
This was a bad idea. The problem got worse during the first few hundred miles, and when Farwell finally acknowledged that something was seriously wrong, here’s what he found:
Not a pretty sight, is it? The scalloped edge of the crown race exhibits a bad case of the damage commonly (if inaccurately) known as brinelling. The steerer tube was scoured, as well:
It was a terminal case. The headset was ruined beyond repair. The only cure? Fitting a new headset. Which is what Farwell did.
The takeaway message? Check your headset often, and if perfect adjustment — neither too lose nor too tight — eludes you, don’t settle for good enough. Find out what’s wrong, and then put it right. Or have your local mechanic do the job for you. That’s probably the wisest course, in fact, since problems that can’t be resolved with a simple adjustment or lubrication often require replacing the headset, and this requires either specialist tools or a highly developed knack for improvisation. It’s not really a job for a rank beginner.
In other words, use your head. Keep your headset properly adjusted and lubricated. And when trouble surfaces, have it seen to without delay. That’s the only way to head off headset problems.
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