Mild front end wobble

My bike exhibits a mild wobble of the forks and bars almost any time I
remove my hands from the grips. It is present at any speed and never
increases in amplitude so it's not too scary. It immediately damps down
to zero when I grip the bars again. Because I can't accelerate without
grabbing the bar, I don't know if that would stop it.

Still, I would prefer not to have this situation. Anybody have
suggestions on what causes this and what will stop it?

So far I have checked the rear swingarm bearings, the head bearings, the
front wheel balance, and the tire pressures. All OK. There is no
uneven wear on either tire.

All motorcycles are single tracked, front steered vehicles, so I don't
think the make matters much, but it's a Royal Enfield, an old Brit.

 

I wouldn't.

Brinnelling. Nothing to do with old Isambard at all.

Except that a notchy set of head races produces a different effect. A
sort of gentle rolling motion. So I'm afraid you are wrong here.

<snip>

Worn tyres, mismatch between front and rear in terms of wear, heavy
luggage on the back, or just unsuitable tyres.

Lots of bikes do this to a greater or lesser extent. Don't ride
hands-off.

 

This is probably the phenomenon that Bruce was referring to....

http://www.tribology.co.uk/services/investigate/rb03-4.htm

I've heard of this before. An example I can think of was a story about a
bunch of Japanese cars that were cinched down to the deck of the freighter
by their frames. The vibration of the ship during the voyage caused the
stationary wheel bearings to "Brinnell" (or "false brinnell" as this site
calls it) and as a result they failed prematurely in the cars.

Point contact of the balls on the race makes it almost impossible to keep
the stresses below a fatigue limit, that's why they publish the L10 life for
bearings, the load at which 90% of them are still OK after a standard # of
cycles (10^9 ? can't remember ). But they are supposed to fail eventually
under any load because of this.

Seems fork crown bearings would be a good candidate for this. Especially if
the owner is fond of wheelies and lands hard.

I know people who have had to have these bearings replaced.

But this may not be the problem. Just so you don't think I'm picking a fight
*** my bike will also do this wobble thing at certain speeds if I take
my hands off the bars, it has done so since it was new***.

There's my 2 one hundredth's of a buck.

D.

 

That's interesting. Oh, head races brinnell all right - it's just that
notchy head races show up with different symptoms.

 

The notches that show up in head races are "false brinnelling". This
is common in bicycles as well as motorcycles, and for the same reason.
On a bicycle (or a motorcycle for that matter), the impact loads never
come close to that necessary to actually brinnell the headset. The
phenomenon is caused by displacement of the lubricant, and the
resultant metal-to-metal contact (actually "welding") that takes place
at a microscopic level.

Mark Hickey

 

[Jobst Brandt is a cantankerous, and usually correct, bicyclist who
points out (convincingly) that headset "brinelling" is actually
fretting.]

 

Indeed, the correct term is "fretting". Brinell refers to metal hardness
testing procedures and has nothing to do with wear in any form.
B