Although an improperly adjusted headset won't cause a fire or catastrophic bicycle breakdown, it'll wear out the headset faster and make controlling your bike a little more difficult. Plus, I usually ride 'no hands,' and having a buttery smooth headset that's not too loose is pretty critical to the sans hands riding.
Moreover, by checking the headset you can find many possible problems with your bike (not only headset problems). Much of this instructable is dedicated to diagnosing the problem, which simultaneously diagnoses other potential issues with your bike.
This is actually a really easy thing to check for, and it takes less than a minute to do. After you get the hang of it, properly adjusting a headset only takes a few minutes to do. Don't be scared by all the steps - I'm just trying to be as clear and thorough as possible!
Step 1: Assessing Your Headset
Step 2: Too Tight?
Turn the handlebars. There shouldn't be much or any resistance. Alternately, point the front wheel directly in front of the bike (as if you were riding in a straight line) and pick your bike up so that the front tire is a few inches off the ground. Slowly and slightly tilt the bike from side to side (not front to back!). Your handlebars (and front wheel) should turn as you slowly tilt the bike. If you can tilt the bike 15 - 20 degrees and the handlebars/front wheel don't move, your headset's prolly a bit too tight.
Step 3: Too Loose? Pt. 1
This is usually the case, and unless you know what to look for it can go unnoticed. Stand on the left hand side of your bike, so that the handlebars are in your left hand and grab the seat with your right hand. Grab the front brakes and lock them (with the brake lever, as you usually would wile riding) so the front wheel won't turn. SLIGHTLY rock the bike front-to-back. Your hands should be moving 1/2" or less (in unison, naturally). The front wheel should remain completely stationary and the back wheel should be moving / rolling just a little bit.
You probably don't know what you're looking / feeling for - keep reading and I'll get to that!
Step 4: Too Loose? Pt. 2
Don't move yourself - stay on the left hand side of the bike, keep your right hand on the saddle and left hand locking the brakes, just turn the handlebars (and correspondingly the front wheel). Again, slightly rock the bike back and forth - the front wheel should remain stationary and the rear wheel may rock/turn just a little bit.
Step 5: What a Loose Headset Feels Like
If the headset is loose, you'll feel it in the rocking, both when the wheel is straight and turned.
Although you won't necessarily hear anything, you'll be able to feel a slight 'loose' movement. It's kinda hard to describe, but it's similar to rolling a pencil between the palm of your hand and a desk - one of the pencils with a hexagonal cross section. Aside from feeling the part of the pencil that you're actually touching, as you are rolling this pencil you can sense in your hand the impact of each one of the pencil's faces as it makes contact with a hard desk. The sensation of a loose headset is similar while rocking the bike - you'll detect a subtle rocking/knocking, especially in your hand that's on the handlebars, gripping the brake.
If the headset is very loose, you'll feel a pretty obvious sloppy, looseness in the rocking.
Step 6: What Happened?
As you gently rocked the bike with the front brakes locked, there are a few things that may have happened; each points to a different problem (or problems) with your bike.
1) When the wheel was both straight AND turned you didn't feel any 'loose' movement. You were subtly rocking your bike and that movement was all that you detected.
- Your headset (and probably the rest of the front end of your bike) is in good shape!
2) When the handlebars were straight, you felt the subtle loose movement previously described (or possibly not so subtle) as you were gently rocking the bike AND when the handlebars are turned (step Loose? pt. 2) you no longer feel that subtle loose knocking / movement as you rocked your bike.
- Something is probably loose, but it's most likely not your headset. Your front wheel may not be secure in the drop-outs, or your brakes may be loose (not just the brake pads, but the part(s) that hold the pads, check the bolt that I circled in pink if you have that style brake).
3) When the handlebars were straight everything felt tight, AND when the handlebars were turned you felt the subtle knocking / 'looseness' while rocking the bike.
- Your front hub is probably loose. See the second picture.
4) You get the subtle knocking / looseness BOTH when the handlebars are straight and turned.
- Your headset is probably loose, or some combination of other problems mentioned in this step. If the headset is loose enough, you can see this rocking (most visible where the green circle is on the first picture).
These are the typical problems that I can think of, but it's certainly not an exhaustive list. Additionally, the knocking / looseness may not be so subtle. If it feels like something's really loose, take your bike to a proper shop - it may not be safe to ride!
Step 7: Tighten That Headset (A)
1) Using the wrench, turn the 'locknut' (hereafter 'nut') counterclockwise to loosen everything.
2) By turning it clockwise, tighten the 'threaded top race' (hereafter 'race') I just use my hand.
-- (Informative, but certainly not necessary: at this point really loosen the race too much so you can feel what a headset feels like when it's too loose. Alternately you can overtighten it with a wrench to get a sense of what an overly tight headset is like).
3) Using previous steps 2,3, and 4 check to see if you tightened the headset too much (step 2: Too tight?) or not enough (Too Loose? Pt 1 & Too Loose? Pt 2). The end product is the 'buttery smooth' headset, but don't worry about hitting that mark right now. The goal right here is to get the headset close to buttery, but not properly buttery.
Step 8: Tighten That Headset (B)
NOTE: This will most likely tighten the race a little (despite any washers that may be between the two!), which means the headset will tighten a little bit.
Again, check the adjustment of the headset (turn the handlebars back and forth, then grab the brakes and rock, then turn the handlebars at a 90 degree angle and rock) as previously described.
If your headset is perfect - buttery but not loose, you're done! It's pretty rare that this happens though. Usually at this point it's still just a little out of whack - either too loose or too tight.
Step 9: Tighten That Headset (C)
If the headset is too tight, try turning the race counterclockwise with the wrench. If the wrench won't fit on the flat part of the race that a wrench usually fits on, use a rag over the wrench and tighten on the smooth part. The pictures denote this - the wrench is in the same place in both pics, but the rag is wrapped around the wrench in the second pic. The rag will help protect against scratching the race, but beware - you can easily scratch your race this way.
Yet again, check to see if the headset is too tight, too loose, or just right.
Step 10: You Got It!
It may be a bit tricky at first, but you'll get the hang of it. Like I said initially, this entire process from start to finish only takes a few minutes once you've done it a few times!
Guess where this instructable was made!? I made it at TechShop - http://www.techshop.ws. Sweet place, lots of help, amazing possibilities!