Just got a new frameset, BMC GF02, and I am trying to install the headset. The crownrace appears to be too small. Is there prep work that needs to be done to the fork, besides grease, to make it fit?

Fork crown races are often press fit... on a new fork it is not unusual for the crownrace seat to need milling prior to installation of the bearing race. Also, there are two standards (ISO and JIS) that are not compatible. JIS crown race seats measure 27.0mm and ISO measure 26.4mm. While it is unlikely that you have fork that has a JIS spec crown the fix to install an ISO headset is the same as preping the crown race seat...having it milled to the correct spec. These tools are expensive so a visit to a good LBS which has the proper tools is probably needed.

-j

Too small how? 1mm too small or just won't slip in by hand? As said above, this is usually a press fit and need some force. To be sure, measure fork and crown race with a micrometer (or even with a precise vernier caliper).

I assume his bike has a 1-1/8" steerer or even a tapered 1-1/8" x whatever so there should be no ISO/JIS size question.

As noted, most crown races (or base plates if it's a cartridge bearing headset) are a tight press fit and usually installed with something that looks like a slide hammer. Some cartridge bearing headsets have a split baseplate that does install with just finger pressure but these aren't nearly common enough.

Thanks. it's my first attempt at building a bike myself. Just not wanting to ruin a new carbon fork.

You can use an 1 1/4" pvc pipe in place of a slide hammer, or at least I do. If it is a cartridge bearing then you can dremel to make a slit in the base plate so it's easier to seat. I've never done this myself since the pvc method has never failed me.

If it's like the other CF forks I've assembled, including two BMC SLR01s, it's a press fit. What I do is rig up a two by four horizontally, bevel it's edges to match the crown under the steerer, pad it with a folded up rag, rest the fork crown on that, use a piece of PC pipe that fits over the steerer and onto the crown race, then tap it home with a mallet.

FWIW: It's not actually a race, but a bearing seat. Technically, a race is what the balls in a ball bearing assembly ride on. The balls "race" around it.

Found this video on youtube. Has anyone tried this method. https://www.youtube.com/watch?v=jMo9YNPO_7Y

That would be the PVC pipe method... my technique is a little different as I tend to listen to classic rock when I work.

I also have a Park crown race setter which works just as well as the PVC pipe.

LOL... Park tool? Must have to play Linkin Park with that.

no you have the option of playing MacArthur Park

https://en.wikipedia.org/wiki/MacArthur_Park_(song)

https://www.youtube.com/watch?v=GHS8hj4TdT8

Live performance, with critics, analyzing the singer and Jimmy Webb's composition.
https://www.youtube.com/watch?v=amzJDSsC2IA

So I tried the pvc pipe method and the pvc shattered at the fork. I got mad and decided I would just cut the race, I had seen that as a suggestion. When I pressed it down it spread out so much that it didn't fit inside the head tube. So I'm giving up and going to a shop. I'm hoping they can sell me just the piece I need.

There may have been some tolerance issues between the two interfaces. I've always had success with the PVC pipe, and have used it on almost every brand and size. Like I said, I've never tried splitting the base plate, but at least one person that I know did it successfully. Did you use sched. 40 pvc? FWIW, I had a CK base plate go on loose and they have some of the tightest tolerances out there as far as I know.

Sorry for your troubles, man. Hopefully, you can get it all sorted. What brand of headset/fork is it?

It's a BMC fork with an FSA headset. It was shced. 40 pvc. Looking at the headset it says tapered 1 1/8 to 1.5, so I'm thinking I may have need 1 1/2 pvc. I really don't understand why when it is spread out enough to completely seat on the fork why it is too large for the headset. Wondering if the fork needs milling.

My buddy did not split the base plate out of necessity. It was more for ease of installation/removal when swapping forks. And, yes, 1 1/2" pvc is what I use on my 1.5" steer tubes. I don't own anything that is tapered. The good news is that FSA is a fairly common brand. You should be able to replace it for very little out of pocket, and a good bike shop will most likely install it for free.

My apologies if I misdirected you. I'm also not very familiar with road bikes. Probably should have made that clear in my post as well.

no apologies needed. if was just something I wanted to try and do myself.

Thanks. It occurred to me on my ride that in order for that "trick" to work it may be that the base plate would need to be previously installed first. Probably not such a good idea for a first installation. Hope it all works out for you.

Some FSA headset parts are available, go the the small parts section on the FSA site and see if what you need is.

The part that I needed for a Z3 was five bucks and FSA wanted over $15 shipping for what would fit in a 79 cent padded envelope and take two dollars in postage. I bought a complete Cane Creek headset and Profile Design bars for that bike instead of the FSA dicking.