Hello, Calvin Jones here, Park Tool Company, with Tech Tuesday
in this video we're gonna look at troubleshooting the head
...set. The headset is a pair of bearings
in our head tube that help give a smooth action to the front fork
yet should not have play or knocking. A typical mechanical test is the bounce test.
This one seems very reasonable - turns smooth,
no excessive rattling. Let's look at a different bike.
This bike has much more going on. Definitely some excessive rattle noise
but let's isolate those noises - let's look deeper where they really are.
it can even be a loose cage. This cage is deformed
eliminate that, get it out of here
Next, let's move to the front end.
Here a good test is to lock up the front brake,
grab the stem and rock it back and forth.
Definitely you feel - this is much more feel than a visual thing
were feeling knocking - a resonance, a thumping in our front end.
But there are still several things that can be going on here.
Grab the fork, grab the front wheel,
I pull side to side, I feel nothing. That is appropriate, there should be no play
in the hub bearings. I can rotate 90 degrees,
lock it again, and go back and forth, I still get the knocking.
on this fork, it's good to grab lower and upper right at the transition
I feel for the knocking - in this case there is no knocking.
You move your hands up to either the fork crown
or the top cap, and definitely we can feel knocking right here.
Below, the same thing - I feel motion.
The play is definitely in the headset adjustment.
We need to adjust this headset. We're going to loosen the stem bolt,
we're gonna tighten the top cap, its gonna pull the fork up,
it's gonna push the stand down, press on those bearings and remove the play.
so first we're going to loosen the lower pinch,
We're gonna loosen this upper stem pinch bolt, then we're gonna come here
and we're gonna go maybe a quarter turn, make sure your stem days straight
secure,
then let's test again:
It's not eliminated - it's still there!
fails the same test - I still have motion here
so we need to go deeper.
In fact that's taking off the top cap
So here we can see the source of the problem.
Inside we see the steering column
it is so long it h.as come to the top of the stem
what was going on here is that the top cap is not pressing on the stem
to press on the spacers to press on the top cap to press on the bearings.
It is pressing on the steering column. There is no motion and no preload going on with the stem.
We can take the fork out, we can cut it,
or we can save some time and headache
by adding another small spacer - a headset spacer to the top
effectively lengthens the stem underneath our cap.
That is the quickest way
Reinstall this,
center it up,
loosen the stem bolts,
another eighth or quarter turn - small steps on our bearing judgments
stem's straight
We tighten back and forth, back and forth again finishing with a torque wrench if we like,
and test the bearing play.
No excessive rattle.
no knocking. It's good to go.
So when we have an adjustment that's just not working,
we keep doing it and there's no change, something else is going on.
dig a bit deeper. And that is headset troubleshooting.
Thank you.