Headset question - handlebars sticking straight ahead
 

I just switched the stem on one of my bikes and when putting the new one on I noticed the handlebars really want to go straightforward - imagining straight ahead being 0 degrees, the handle bars turn smoothly 45 degrees either way but really catches while straightforward. It is a threadless headset. I didn't notice this before I switched the stem, but that doesn't mean it wasn't happening. Does it sound like the headset is bad? Or I adjusted it wrong? I loosened everything and it still catches going straight without the star nut cap or stem attached. It probably only has 1000 miles or so on the bike, so I would be surprised if it was wearing out. Thanks in advance

???????

make sure your bearings are seating back in correctly. Try installing the old stem and see what happens. If it only happens with the new stem then its possible that the face on the stem is off yielding uneven compression on your bearings. Yes, sometimes stems do have uneven faces.
Lou

try the old stem as mentioned above.
also keep an eye out for the housing catching/pushing on each other or the brakes or cable stops or whatever. it always seems like a chaotic mess to me.

this is called "headset getting indexed."

if it's not totally screwed up, you can fix it by re-greasing your bearings and setting the preload on your headset a bit lighter.

You should be able to feel the headset bearings 'notch' into position if its indexing, as vqdriver mentioned. For a 1000 mile bike that's unusual unless it's been torqued down HARD.

More likely have a look at the cable run; especially for bikes with headtube stops the cable outer length has to be cut 'just so' to allow untrammeled and straight steering.

The classic 'index steering'

What type of headset is it?

dave

Wow - thanks for all the suggestions. I'm going to start with putting the other stem back on. It's a FSA headset - kind of generic looking. It came stock on the bike, which is a Rocky Mountain Sherpa 30. It really almost locks in totally straight, and is smooth outside of anything but straight ahead.

+1 on being indexed. Since the headset spends so much time in one position it can develop wear in the races which will tend to trap the balls in that one place. Can be made worse if the cups installed perfectly, if it's been torqued down too hard, or if there's some odd differential pressure like the stem suggestion.

That said, I've been able to delay the inevitable in the past by disassembling the front end, spinning the bearings a bit (so the balls go to a different place in the race) and reassembling. Won't fix the problem, but at you'll reset the indexing clock.

Brunelled.

didn't know he worked on bikes.

http://espn.go.com/nfl/player/stats/...5/mark-brunell

A "fix" I have found for an indexed headset is take the HS bearing cups out of the frame and rotate one 90º clockwise and the other 90º counter-clockwise and reinstall.

right on.

dave

Thanks again for all the suggestions. This forum is great for getting knowledgeable people to give good answers. I googled headset indexing and it sure seems to meet all the symptoms - especially the "snapping" into place I found reference to on Sheldon Brown's website. Looks like I finally have a use for an old headset I saved just in case.

I use a marking pen and put a dot on cups before taking them off so I can
set them back at 90º .

http://i48.tinypic.com/2v3n71l.jpg