How do I know when to replace my headset? The seal has been broken (plastic piece on a 105 headset) for quite some time. I used to ride in the rain alot but not so much any more. There is a slight bit of friction in the headset but how much do i allow for before I replace it?

Also is this a job I can do myself? Do I need special tools? If so then is it more cost effective to have the bike shop do it?

Thanks.

By "plastic piece" if you are referring to the top cap, then that is nothing to worry about and does not indicate your headset is broken. It is used to initially set the tension on the headset, but once the stem is tightened serves no purpose. Read this, should answer most of your questions regarding headsets:

https://www.parktool.com/repair/byreg...mageField2.y=9

There are 2 times to replace your headset, when it breaks, or you are getting a new fork. They wear in together, and its important that they get replaced at the same time.

The headset bearing and the crown race are what wear together, not the fork. Headsets do wear out instead of breaking.

First, repack the headset. When headsets go bad they usually dont turn smoothly and "lock" on center. This happens because the headset was loose and when you hit a hard bump, all the force is on one bearing, which dents the crown or race. Tighter is better with headset adjustment. It spreads out the force along all the bearings.