Need advice on threadless headset that keeps coming loose
 

I've got an 1 1/8" Cane Creek headset on a mountain bike that has been switched over several times to other frames over the past 10 years or so. I just used it on a parts bin bike I put together and it keeps coming loose after each ride. I have to loosen the bolts on the stem, then really crank down on the cap bolt that goes into the star nut, then tighten the stem again. The result is the steering feels tight. Is there something to look for or have I finally just installed/removed too many times?

Thanks

First an most obvious, especially because you're cranking down.

Are you sure the steerer ends short of the top of the stem/spacer stack and that the top cap isn't bottoming against the steerer? Note some top caps, are stepped, and need extra recess of the steerer so as not to bottom.

The second most popular is a crown race or headset cups that weren't fully seated. As you ride, they settle deeper throwing off the adjustment. Also, this can mean that a stack height that seemed adequate when you put it together, may no longer be, so check that anew.

Lastly, but more rare is a stem that simply doesn't clamp tight enough. I wouldn't look here until you've confirmed that the other two causes don't apply.

also make sure the split compression wedge is present

One other thing that I'd check is the head tube shape. Pull the headset cups and measure the head tube top and bottom, both front-to-back and side-to-side. If the front-to-back measurement exceeds the side-to-side measurement your head tube has been ovalized. I don't know how to fix that.

I'm betting that you just need one more small spacer. If there isn't a 2 or 3 mm gap at least between the steerer and the top of the stem or spacers, then the top cap will never be able to fully tighten down .

I didn't think about that but I agree that's the mostly likely scenario.

Number of ways, epoxy, steel cups that have ghetto knurling performed, aluminum shims from a Miller can (has to be Miller) in a flower arraignment around the headtube with some locktite that is used for taking up volume, can't remember the number, but could find the number if felt compelled. Any of these will work, choose your method.

How many of them have you actually done?

So I pulled the headset apart today. I had installed the top sealed bearing upside down in the cup. It looks to me like the resulting rocking back and forth "ovalized" the cup, as RetroGrouch was talking about. I flipped the bearing over and the fit is tighter, but alas, the gap isn't something that can be completely solved and it looks like I've finally killed it. It's a testament to how these can last though, it's got thousands and thousands of miles on it and has been installed on at least 4 bikes. And even then is wasn't worn out; it would still be running strong if I hadn't flipped that bearing and ruined it.

I have done two different Bridgestone MB frames with a Steel Campy record headset with ghetto knurling. This method was suggested to me by a local mechanic with decades of experience. The bike shop owner who suggested epoxy or JB weld has done many on his own bikes, as he is a old MTB racer. The flower method is from a reputable frame builder over on the Velocipede forum. That method works great as I set one of my Bridgestones up with a aluminum cup headset without the locktight to see if it worked. It does.