Low speed wobble - steering stem bearing adjustment

[lamoun]

    My front end would make a cracking nose while braking for some time now, also there was a front to back freeplay on the front wheel.

    Today I decided to take my sorry ass and adjust the steering stem bearing. At first I tighten the bearing nut a bit (living some front-back freeplay) and rode the bike around the block. I could feel the handlebar wobble slightly - left to right - with a frequency about once per second. I tighten the nut a bit more to eliminate the freeplay and the wobble got much worse. Riding at about 25miles/h and leaving the handlebars the bike would weave across the road.

    Finally I slacken the nut (very difficulty - so it was already over tighten) and screw it slightly. No freeplay and very little wobble. I'll try to screw it less tight and see if it totally eliminates the wobble.

So the million dollar question. Why tightening the bearing nut will cause, or amplify, steering wobble?

Something similar I found http://gstwins.com/gsboard/index.php?topic=18397.0

[tt_four]

Ideally, those bearings should just be tight enough that nothing has any play in it, but that the front end still moves freely with no friction. If it wobbles when you're riding the bearings are probably adjusted too tight, and they're not moving freely, which makes the handling react weird.

If you can't find a happy medium, that means the bearings are probably shot. They would need replaced. Cartridges can usually be overtightened and still feel smooth, even though they'll wear out faster, so it's hard to say what's actually doing it. The other thing to keep in mind, is that when you tighten the one nut, and feel like the adjustment is perfect, and then you tighten the locknut, the first one moves and takes it out of adjustment. You usually have to over compensate and play with it until it feels just right.

[johnny ro]

I thought there was supposed to be a small amount of preload in an adjustable rolling element bearing, to ensure all the rolling elements are given a chance to make contact and one largest ball does not wear out right away.

[tt_four]

I don't know. Your response sounded way more technical than mine did, so you're probably right.

[The Buddha]

What were you tightening.

Of you were tightening item #10 in the diagram with the handle bar plates removed ... as in, tightening  with a C spanner or a proper socket spanner and trust me, they exits, but I made mine from a socket and it is attached to me surgically ... it aint getting away ... life saver ... Anyway, it cannot put in a wobble if it was tightend, uness it was waaaaaaaaay loose to begin with amd you tightened it a hair.

If they were indeed loose, I would open it clean it and re grease it as look for flat spots.

If you were tightening item 15 ... WTF ... any damn thing can happen, its the wrong item to fix the issue. Your bike is coughing and sputtering and to fix that you're replacing turn signals ... yea that is about close enough.

Yes bearings have to have a light preload, I like to hand tight with my socket with the front wheel sitting on the ground ... as i ints on the center stand with wheel making contact with the ground and I hand tighten the collar, and back off 1/4 turn.

Cool.
Buddha.

[lamoun]

I was tightening #10, with #15 and #12 removed.
Ahh, in every case the steering is smooth, the only difference is the wobble and the front end freeplay.

[sledge]

The accepted way to check headstock bearing preload is correctly set is to use a springbalance and pull the bars horizontaly with it. The setting is a barn-door, 200-500 grams so aim for 350.

Loosen the stem-head bolt  (the large chrome nut directly below the keyswitch) and the two upper fork-clamp bolts so the top clamp is free to float up and down then make the adjustment on the locking ring, retighten the stem-head bolt to 35-55 (aim for 45) Newts and the clamps at 18-28 (aim for 23) Newts and check with the springbalance. Repeat until you hit the barn-door. If you cant get the correct settings or are still getting clunks and a wobble the bearings are shot.

Nothing kills headstock bearings better than water ingress, use the bike a lot in the rain or God-forbid pressure wash it on a regular basis and you are going to have problems sooner rather than later

[The Buddha]

I was tightening #10, with #15 and #12 removed.
Ahh, in every case the steering is smooth, the only difference is the wobble and the front end freeplay.

Remove 15 and 11 and tighten 10.
Cool.
Buddha.

[tt_four]

Yeah, if it's wobbling, as in the front end moves independently from the frame, it's definitely too loose. What I was talking about, with it being too tight, is more of the front end just not responding to the affects that normally turn the front end of a bike. If you rode a motorcycle by steering the front wheel in the direction you wanted to go, it wouldn't happen. Instead it would just feel like the steering was tight. Because you do the opposite, and push the bars in the opposite direction and let the lean of the bike actually turn the wheel where it should go, that's when you run into handling problems from the bearings being too tight, because you want to turn right, so you push on the right handlebar, the wheel goes left, the bike drops to the right, and instead of the front wheel steering itself to the right like it's supposed to, the bearings give too much resistance and you have to manually turn the wheels where it should be. That doesn't sound like what you were originally describing, but I figured I'd throw it out there since you hadn't really diagnosed your problem yet. I've gone through that problem before when i was younger on bmx bikes when the headsets had problems of coming loose. I would just try to overtighten them, and then you'd actually have to steer the bicycle everywhere. It's much more noticible on a 20lb bmx bike than it is on a 400lb motorcycle though.