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What causes steering cup indentation?

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What causes steering cup indentation?

Old 03-10-19, 12:48 PM
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What causes steering cup indentation?

So...this morning I took my bike out (Dawes Ligntning)...and immediately noticed funky steering. It's like it has auto-return-centering on the steering. At normal speed or higher, I don't notice anything unusual. But at slow speed, I notice the steering is like I have a low psi front tires or something. Slower the speed, the worse it feels.
I pulled over onto the side of the busy highway...and turn the handlebar left and right. It feels like there's an indentation on the steering cup. I will pull bearings and cup out tonite and rotate the cup by 180 degrees. In the meantime, I'm investigating the cause...

I recall hitting a bump in front of my drive quite hard last time after I was on my way home from a group ride. I recall stopping to check to see if my rim was bent...it did not...and I recall breathing a sigh of relief. Strange thing is I hit this bump with my other bikes (all have wider tires) without ever any problem.

So, now I am left struggling to make sense of this incident.

Theorys of cause:
  1. Not enough tire pressure? I am running 25c tires, and I run 85 psi for comfort.
  2. Cheap stem headset? It a quill stem and looks like a Tange headset...not sure though.
  3. The stem bearing was adjusted too tight?
  4. I was putting too much weight on the handlebar. I recall feeling the harshness thru onto my shoulder...must be my elbow was locked.

Wat say you all?

Last edited by mtb_addict; 03-10-19 at 01:20 PM.
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Old 03-10-19, 01:13 PM
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How old is the headset? The usual cause of indenting is the repeated scrubbing away of the lubrication from small steering motions, ie riding a straight line. Fact of life of a bicycle headset. More lube will help - a little. Being BMX and doing regular wheelies and full handlebar spins would help a lot.

Your headset will only get worse. Rotating a cup will slow the decline. Changing the balls out to one size larger will buy you about a thousand miles. (It will also open up the tight clearances designed t keep out water and grit but you no longer have a HS worth saving so that doesn't matter.

Start your search for a new headset.

Ben
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Old 03-10-19, 01:22 PM
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Originally Posted by 79pmooney View Post
How old is the headset?
Ben
Bike is a NOS from Bikeisland (Bike Direct). The bearing is practically new...because the bike gas been sitting in a warehouse for a few years. WHen I first got the bike (a month ago), I did unscrew the lock nut and top cup to peek at the bearings...and the bearing grease looks good (shiny, translucent, and creamy, and generous amount)...so I left it as is.

Last edited by mtb_addict; 03-10-19 at 01:27 PM.
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Old 03-10-19, 01:31 PM
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Is it only in the centered steering position that it sticks? Or are there other sticky spots as you steer to the sides?
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Old 03-10-19, 01:33 PM
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Originally Posted by rseeker View Post
Is it only in the centered steering position that it sticks? Or are there other sticky spots as you steer to the sides?
Only when center position. That is the only sticky position.
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Old 03-10-19, 01:35 PM
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I think it is also possible the problem has been there since the beginning and I just never noticed it. Becuase it only manifest itself when it is going slow. And I usually don't ride slow on this bike. I ride slow today...because I was commuting to work.

If this is the case, that the factory could have over torqued the bearing...I guess.
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Old 03-10-19, 02:32 PM
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Most likely the bearing adjustment was too tight. Impacts from most riding will not damage the bearings. After you looked at the grease did you gently adjust the bearing by getting the pressure just right so there is no play but no resistance to turning and then locking the locknut against the top bearing cone?
Is it possible you tightened the top cone adjustment by tightening it like a nut and bolt? That will push the balls in tight enough to make a dent. A lot of people make this mistake. Before I knew better I did it once too.
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Old 03-10-19, 03:25 PM
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I have an old Cannondale with a lot of miles that had the same problem. Rotating the bottom cup 90 degrees solved the problem.
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Old 03-10-19, 05:44 PM
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i diassemle the head set...wipe the cup and cone clean...and I see the headset is in perfect condition!

i slab some axle grease on there and put everything back. Now no more problem. Wierd!

so...my guess is the bearing had self-tighten somehow...bearing got too tight maybe...perhaps when i hit that bump, the shock torque self-tightened the adjustment cup..that is only explaination i have. if so...strange...never have a bearing go tighten on me.
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Last edited by mtb_addict; 03-11-19 at 08:13 AM.
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