I recently had the occasion to remove the stem off my second bike in an attempt to install a new one. The new one would not work, so I had to put the old one back on. I had this bike built up by a LBS when I got a new frame. Some of the parts from this now 2nd bike were put on the new frame and some parts had to be bought new, i.e., the stem. I assume it was all done properly, they are a reputable shop. The stem is on a carbon fork (not sure of the size, however).
My question/problem is that when I went to put the old stem back on, I noticed that the stem's diameter was actually too big for the diameter of the fork. Meaning that the bolts could not be tightened sufficiently to allow the stem to secure to the fork. The only way to get the stem to fit snugly on the fork was to tighten the compression plug on top.
Now, the stem is secure on the fork and will turn the fork when the bars are turned. Whereas before tightening the plug the stem would just spin.
Having never done that type of work before, I was wondering if that was proper. I have seen some videos where the stem fits somewhat tightly on the fork before you even get to tightening the bolts.
Is mine situation just one way to do it or totally wrong?
Thanks and I hope that my question makes sense?

What's the diameter of the new fork's stem? Measure your old one and compare it to the new one to make sure they're the same.

There's something wrong with your setup. The top cap is only to provide bearing preload, and the stem should definitely close tight around the steerer tube.

Could it be that your bike originally came with a quick-adjust stem?

Some bikes have what's basically a thick shim that goes over the steerer tube first, and takes the compression from the preload. Then the stem goes over the shim and clamps down around both shim and steerer in the normal fashion. But with the shim doing the preload, the rider can adjust the stem up/down the whole length of the shim w/o having to worry about the headset adjustment going wrong.

RUN, do not walk but run to your nearest LBS and have this corrected. What you are describing is very dangerous and must be corrected properly. The stem must clamp securely to the steerer tube and if yours doesn't it's a serious accident waiting to happen.

Thank you both. I figured that something was wrong when I took it apart. The bike is an older steel Ciocc to which I added a carbon fork. I think it's a 1" fork. I'm very surprised that this LBS would have screwed this up so badly. Is it possible that a shim or spacer of some sort fell out and I didnt notice it or is the stem supposed to fit snugly and no spacer of any sort is proper?

The stem is supposed to be a snug fit, usually direct - but there are 1"-to-1 1/8" shims - which'd make sense as 1 1/8" stems are far more common than 1" (threadless) stems. And apart from losing a few style points, there's nothing dangerous or wrong about using them.

Possibly the stem had a sleeve or shim in it and you have not reinstalled that?

Although HillRider mostly said it, please do not ride that bike at all until the stem is fixed.

Thanks, I didn't see any sort of shim when I took it apart, but I can't understand how the LBS messed it up. I will have to go check it out.

Perhaps what the OP has is a 1" threaded fork, Nashbar makes a carbon replacement, and his stem is mounted to a quill adapter and tightening the "top cap" is snugging the bolt in the adapter. But, having a compression plug confuses me and probably throws my theory out the window.

Well, maybe I mislabeled my top cap and called it a compression plug. It very well may be a 1" threaded fork, I got it a few years ago and don't remember the specifics. Like I said, it's an older steel bike that came with an quill stem and steel fork. I replaced the steel fork with a carbon one so it might be of the threaded kind. Does that change anything?

Can you post pictures of the stem and fork and headset?

Sure, I will try that tonight when I get home

The odds of you having a carbon fork with a threaded steerer are really, really small. Having a 1" steerer with a shim for a 1 1/8" stem would be far more likely.
Do you have a vernier caliper? Or failing that, an adjustable wrench and a ruler? Two quick measurements of the steerer and the stem diameter would settle this nicely.

Will check that and pixs tonight. Update tomorrow!

OK, so here are some pictures of the stem : I think you can see space in the second photo between the fork and the stem. It's obvious that the diameter of the stem is larger than that of the fork. The last pix is of the "cap" or "compression plug" whichever it is.

You have a 1" threadless steerer and a 1-1/8" stem. The 1-1/8" to 1" shim that goes between the steerer tube and stem is missing. You MUST get one or purchase a stem that fits a 1" steerer. The compression plug is used to set the headset preload and the stem bolts then are tightened to hold the setting. After that the plug is not essential but does keep water, etc, out of the steerer.

thank you. I can't believe that the LBS did not install a shim. I don't think I dropped it, but could it have slid down the fork?

Come on man, the bike shop did nothing wrong. If there were no shim, you would have crashed on the first ride. You lost the shim when you tried to install the new stem. Just bring your bike in to the shop and get it fixed.

It will not slide down the fork as it won't clear the headset's top cover. It was left out by someone, either you or the LBS.

Wrong! The bike has not been off the trainer since I got the stem installed.

Thanks, I saw that once I looked at it closely. I think I would have seen the shim if I lost it. The bike is on the trainer and hasn't moved.

I know you really want this to be the fault of the LBS, but I seriously doubt it. They correctly ordered the uncommon sized 1" fork and headset for your Ciocc which shows a certain amount of knowledge. I find it hard to believe that they would then put the wrong size stem on there with no shim. I also find it hard to believe that you wouldn't notice that there was something wrong right off the bat, even if it was on your trainer. The stem/bars would move too easily with only a compression plug holding them on. Just get the bike fixed if you plan on riding it and chaulk it up to mechanical inexperience. Maybe you could look at it as punishment by the C&V gods for installing a threadless carbon fork on a classic Ciocc and then riding it on a trainer.

Actually, that isn't the case. I don't want it to be anyone's fault, but it seems like it is. I've spent a small fortune at that shop so I too would like to believe that I misplaced the shim. That's highly unlikely because the bike is in my basement on the trainer and nothing fell off. As for the stem/bars moving too easily, the problem is that with the compression plug tightly secured, the stem does not move especially while on the trainer where I do no turning. Isn't it possible that they just screwed the plug in and figured that that was good enough or they made a mistake?
As for the C&V gods, I prostrate myself seeking forgiveness. At the time, I wanted to lighten up the bike so swapped out a beautiful chrome fork for the carbon . If only!!!!

I guess it's possible, but unlikely. The shim is inexpensive: https://www.jensonusa.com/Problem-Sol...1-To-1-18-Stem. Order it up, put it in there and try to install the stem. Just put the stem and shim on with the clamping bolts loose, tighten down the compression plug until there is no play on the headset and it turns without too much drag, then tighten the clamping bolts on the stem. If all else fails, hopefully you kept the original fork. If the LBS took it, then yes they screwed up.