I bought a nice Craigslist find this weekend, a Cross Check with a Chris King NoThreadset. Anyway, when I took it home I noticed a fair amount of play in the headset, so I decided to tighten it. I loosened the stem bolts first, and then started to tighten the cap bolt, checking the play with every half turn or so. Anyway, I wasn't noticing any improvement in spite of the cap bolt getting tight, so I (probably foolishly) kept turning, and then I heard a snap! Now the cap bolt can be turned indefinitely without getting fully tight (it will appear to get tight and then a quarter of a turn after that will bring it back to being loose), and of course there's still just as much play in the headset. So my questions are: what the hell was going on with the headset in the first place that the cap bolt was tight without a corresponding reduction of play? And did I break the star nut? How should I proceed?

what was the snap is the question..did the cap bolt crack? did the threads on the fork stem strip? Find out what the snap was,,and replace or repair it. There is no need to loosen the goose neck bolt to tighten or loosen the fork bolt. It might of been frozen when you went to tighten it,,it just snapped,,,happens

The OP is asking what the snap was, so why would you expect him to know what it was?

That's what he's trying to do.

Yes there is. If you don't loosen the stem bolts all you are doing is tightening the top cap bolt (I don't know if there is a real name for it, so I'm calling it the top cap bolt) against the stem, adding unnecessary torque to the bolt without actually tightening the headset.

WTH is a fork stem??

I think you probably stripped the bolt and star nut. Time for new ones. Shouldn't run you any more than $30. Did you forget to loosen the stem bolts before you tightened toe top cap bolt? This is a very common mistake.

Sorry howeeee, I have to be a dick sometimes to make sure that wrong information like this does not get passed as truth.

Probably the starnut or bolt were damaged or stripped when the prior owner tried to adjust the headset without loosening the stem first. Or possibly there's no centering cone, so he forced it, but it still couldn't tighten.

That's just speculation, but probably not a mile off, and it would have been nice if the seller mentioned headset issues. but thats water over the dam now,

Step one assess your situation. Remove the bolt (if it'll screw out) and lift off the top cap. If the bolt won't back out, you can sometimes get it started by using the loosened stem to put some upward pressure on the top cap as you try to unscrew the bolt. If that fails you'll need to resort to extreme measures to remove the top cap (if this is the situation, post anew, and I'll give you some ideas)

1- is the stack height enough so the top of the steerer is recessed below the stem or top spacer or by 2-5mm? If not you need another spacer?
2- is there a centering cone for the top bearing, and does the lowest spacer, or the stem press on it without touching the surrounding top HS part?
3- is the star nut OK, or stripped, or damaged, and is it broken enough to come out (they usually aren't)

If all is OK except for damaged starnut stuck in the steerer, the easiest solution is to use a punch to push it about another inch deeper and abandon it there. Put in a new starnut with a new bolt and you're good to go.

+1 on FB's suggestions.

If you have a stripped bolt, it's not hard to simply find a replacement that should fit and have the correct length, or if you notice that the spacers stack barely clears the top of the steerer, then adding a 2mm spacer shouldn't look too hokey, and then you can kept star-nut and bolt as is and tighten using threads that aren't stripped.

If star-nut and bolt are both compromised, pushing the existing star-nut down is the exact solution I use too. I gotta bag of these, and the main reason, I think, is because half the folks who service these bikes seem to have a bad habit of over torquing the top bolt -after- they've already adjusted the headset for play, or they simply don't leave enough spacers and are tightening against the steerer tube.

If you're missing the centering cone for the headset, well, you may need to get one to replace it. That may mean contacting manufacturer or having the LBS do that for you and order the part. The headset shouldn't be ridden without this.

If you need to ride the bike now and you're not missing the cone, it may be possible to simply loosen the stem bolts and then firmly press down on the stem near the steerer tube and then tighten up. There may be some play, but if you have a strong enough person to manually "squeeze" the headset per se, then you may be able to snug up a stem bolt just tight enough to prevent slip, then relax and complete the tightening process for both stem bolts to secure the headset in place. The tightness may actually be pretty close to using the top bolt/cap to do the preload. So this will give you time to source replacement parts.

I have only refurbished about 300 bikes in the last three years and keep about 20 riders for myself,,when the headset comes loose I tighten it, never loosening up the gooseneck bolt and never have I heard a snap ...but I am glad you know you are a dick.

You do know that the OP is talking about a threadless headset, right?

Yes, I think Howeeee is still with the threaded headsets. It would be hard to snap something on those, for sure.

Either he is a dick, or you are ignorant and don't know it (the worst kind of ignorance).

I vote for door #2.

Nahh, it's definitely both.

#1 is often a cause of headset adjustment problems
#2 Maybe or maybe not. The OP's bike has a CK headset. Older versions did not have a centering cone but relied on an O-ring in the top bearing cap to keep it centered. Newer CK headsets do have a centering cone.

In the context of my post O-rings and centering cones are equivalent since they serve the same function. I know you're pretty diligent about checking the details of the various components. I don't have the patience for that and prefer to think big picture.

In any case, the OP got the info 4 days ago and hasn't been heard from since. I guess he too the info and ran, fixed his bike, and didn't hang around for the howeeee and AlphaDogg show.

The KK headset cap bolt is usually tightened to about 6 in. lbs. of torque. If you reefed on it hard enough to strip something, it was tightened way too much. I'm not positive about the torque, but that is easy to check.

"Taking care not to shear o-ring, slide bearing cap, any spacers, and then stem over steerer tube. Place stem cap on top of stem and insert screw through cap, threading into star nut. Tighten approx. 4-10 in.-lb. (Max. 15 in. lb.)"

https://chrisking.com/tech/tech_headsets