After playing around with the spacers to adjust the stem height, I cut the steerer. For the perfect height it turned out that the top of the steerer is flush with the top of the stem, which wasn't exactly what I intended. I know I will need a 3mm spacer above the stem. Is this OK since the spacer floats a bit, or will the cap, once everything is tightened, hold it without any problem?

Cut the steerer again. Or put the 3mm spacer under the stem, it's only 3mm.

Personally, I wouldn't do this. YMMV. You can't move the stem up just that 2-3mm and put 2-3mm of add'l spacers under it? You're really that dialed in?

Yes, it's fine to let the spacer 'float'.

I'd take another 2mm off the steerer. I would not put a "floating" spacer above the stem. Not from a safety perspective, it simply seems like a cheesy way to complete a bike build.

O.K., why does he need the spacers above the stem...? I thought OP said the perfect height was top of steerer to top of stem. Someone???

You need a 2-3mm gap to preload the headset before tightening the stem. He cut it flush.

Flush (zero gap) means you cannot torque the stem down onto the headset to get the slop out of the bearings.

You get it by either cutting the steerer correctly, or by leaving something like 7mm of steerer above the stem and putting a 10mm spacer on that.

It's not a safety issue at all. The top cap can do anything it wants to once the headset preload is set and the stem clamp bolts tightened. The OP could use the spacer to get the adjustment, then remove it and put the cap right on top of the stem if he wishes or just leave the spacer there. No harm either way.

Vpiuva- Yes it is that dialed in.

I tried both 3mm higher and 3mm lower, but, it wasn't quite right. I think floating it will work since the cap has a grove so that it fits inside the spacer. That should hold it OK, but I just wanted to double check before cutting it again.

Yes, which is why I said it wasn't a safety issue in my original post. Thanks for corroborating that.

Of course he could just preload the the bearings with the squirming spacer and remove it. If he wanted to use the top cap (which while doing nothing, certainly looks better) he'd have to hope he didn't have one with a convex or raised bottom. Because then, it wouldn't fit in situation where the steerer was flush with the stem.

I'm pretty persnickity when it comes to building bikes, and I think there are two ways to do steerers. One, you cut it 3mm below the top of the stem and two, you cut it longer than the stem and put enough spacers on it to allow the 3mm for preload. Having a spacer sitting on top of the stem supported only by the bolt seems pretty lame to me. No real mechanical reason, just lame in its own right. Although I suppose that while you were preloading the bearings it could move a bit from side to side and scratch the top of the stem. Or perhaps move or allow the fixing bolt to bend if it received a good rap. Idle speculation, but neither of those things can happen if it's installed properly.

Yes you did and I appolgize for misreading your comment.

Even when everything is adequately dialled, I like to have some play available. It's nice to be able to raise or lower the bars without scrapping the bike.

So what would I do? Use either a 2 mm or 5 mm spacer on top of the stem. Use just enough to hide any gap that would show between the stem and its cap. It's nicer that way and in terms of looks, you will hardly notice any difference between 0 mm and 2 mm of spacers at the top of the stem.

Safety and engineering wise, you could use a 10-mm spacer (or whatever you have) on top of the stem to preload the steerer and tighten the stem in place. After that, you could discard all that and leave the steerer open. Not nice, but sturdy.

Also a real effective rain and dirt catcher.

Run it.

In my first post I suggested cutting the steerer again, which if the OP can't or won't change the stem hight, is the only option because the configuration is not right, and will always be just a cobb job.

This is the thing I just don't get about this entire discussion. As you've suggested, cutting another 3mm off is the way to go since it's currently flush. That won't change the set-up of the bike. It won't lower the stem. So I'm just not clear on the reluctance to cut it.

If it isn't necessary, why cut it?

Because that's the correct, no muss, no fuss way to do it?

I just like building my bikes the way they should be built. And "should" is a very personal thing. If it works for you to have an unsupported spacer on top of the stem - that's grand. I'd take the extra 15 minutes and cut it.

Just cut the stem again. Takes just a minute.