Ricanfred

About 1500 miles only on the bike with a properly adjusted and torqued stem. I can replicate the knock when I push on the handlebars with force. Many times it does it when I am mounting the bike and the handlebars are turned. Climbing out of the saddle also replicates it. Got frustrated so I took it to the lbs. They say they have not been able to isolate where it's coming from and will check the headset next. Any ideas, shot bearings maybe, or ???

lasauge 

The headset is the most obvious point of consideration, since that's where all the moving parts are. Definitely replace the bearings and check the condition of the races.

AlphaDogg

If he has such a new bike, it's very likely has cartridge bearings. Cartridges are sealed, and thus require no maintenance. If torqued down to the proper preload, the headset should work well.

Ricanfred

That's what I thought. Maybe I'll just have to deal with the noise. LBS says it can take them days to figure it out. I just want to ride it as much as I can before the snow comes.

lasauge 

Just because the bike has sealed cartridge bearings does not mean it's permanently impregnable. Nor do they make damage, installation error, and manufacturing defects impossible. Inspecting the headset and perhaps replacing the bearings is a simple process, and if nothing else, would allow you to cross one more possibility off your list of possible causes for this knocking feel.

Ricanfred

Noted and thanks.

AlphaDogg

I didn't say any of that. I said that cartridges are sealed and require no maintenance. When I said maintenance, I meant flushing the old grease regreasing with fresh grease. They can, as you said, wear out. They can get also contaminated, though that doesn't happen often. Also, replacing the bearings is not like with loose balls. You have to replace the whole cartridge.

Bill Kapaun

Have you tried applying the front brake and rocking the bike fore/aft?

Ricanfred

Yes, no noticeable play between headtube and fork.

mechBgon

I had that bike at one point, and am familiar with the headset. A couple questions:

1. have you, or the shop, confirmed the cartridges are installed in the correct direction? Sounds dumb, but I had to fix a bike yesterday where they had the lower bearing cartridge in upside-down.

2. if you happen to have a stem that has an angle-adjustment cam between the steertube and the stem proper, then you need to have the accompanying offset-hole top cap, and it needs to be oriented in the correct direction. Trek doesn't have any stems like that, but if you retrofitted a stem of that type, e.g. Specialized's popular ProSet stem, then address this.

3. if the headset parts haven't been greased, it's never a bad idea to liberally grease all the contact areas. You do want those cartridges to come out someday

4. confirm there's an air gap between the upper headset cone and the frame. If not, install micro-spacers between the upper wedge ring and the headset cone.

5. try to rotate the headset cone and spacers. If they turn by hand, the headset needs more preload.

rithem

pick the bike up drop it on the ground a few times (rubber side down) listen for the sound, also turn front end full 90 deg on the ground grab front brake & rock the bike for and aft feel the top cap and top of head tube interface while rocking, you are looking for even the slightest hint of play, odds are the headset needs adjusting the the tiniest bit of play will make a knocking sound especially over rough roads. Sounds like you hit the breaking period time to check everything. Don't over think this just make sure the headset has right free movement with out play.

DieselDan

The quick-release skewer can be slightly out of spec and cause this kind of knocking sound. I've dealt with it, on some decently equipped Diamondbacks, by packing grease inside the hollow axle. Sounds a bit crazy, but it worked.

Wayne Meuir

Had this happen on my old Lemond bike and fixed it by changing from carbon fiber spacers on the steerer tube to aluminum one that fit the tube diameter better. The carbon fiber ones were just a bit loose. Aluminum ones fit really nice and tight.
Also, make sure the cap on the steerer tube is not bottoming out on the top of the steerer tube before the stem/spacers gets tight.

Ricanfred

Thanks for the suggestions guys. LBS mechanic called and said there was a lot of debris in the lower crown race. Cleaned, lubed, and adjusted it all and said the noise disappeared. I'll find out today and keep you all posted.

Ricanfred

Very smooth but noise started again, with a vengeance, about 10miles out. Sounds like a "tick" now. Back to lbs it goes. **sigh**

Kimmo 

Bummer.

You could have just put a little bend in it... sound crazier? Bonus: a bent skewer gives you wider modulation over bearing preload when you set and tighten the QR.

mechBgon

Perhaps the crown race isn't a good fit on the fork. If that's the case, some Loctite 680 might do the trick.

Ricanfred

mechBgon, thanks for all the detailed suggestions! Update: LBS was able to eliminate the sound by switching the cf spacers for alloy ones. They then took the alloy spacers out and put the cf back in and changed the order/orientation they were originally installed. Seems like that worked. Riding tomorrow so will update. Thanks again to you all.