Headset issue...

I'm probably being massively stupid here, but...

I've recently replaced some 1" threaded Time forks with some 1" threadless. I bought a Cane Creek S2 1" headset to use.

I've gone to fit the forks today, and run into a problem. I fitted the crown race and the head tube races without issue, and popped in the sealed bearings. I then went to actually put the fork through, and I cannot push it all the way: the 'lip' of the fork steerer catches on the lower head race. I dismantled everything to have a look, and the lower head tube race seems to be too small for the 'lip' section of the fork. This is a bit odd, as the crown race is the right size (if a little tight). I tried the lower head tube race from the old threadless headset, and it fits fine, sliding over the 'lip' section no problem.

Have I just bought a dodgy headset in the S2??? I'm a bit confused. I can't find much info about the fittings of it, I just assumed all 1" threadless would have the same inside diameter for races.

Image to show the 'lip' section:

Very carefully file or sand the lip away, doesn't take much. Done this twice now and been fine, although my issue was installing the crown race over said lip.

Thanks for the advice, but I don't really want to do that! The crown race fits fine, so in theory the bottom cup should have a slightly larger diameter that fits with zero friction (I can't even get it over atm). The fact that my old cup fits fine tells me it is an issue with the headset.

On closer inspection, Ribble appear to have sent me the wrong headset: a CC 40 EC30.

The plot thickens...

You haven't installed top cup in bottom have you?

You haven't installed top cup in bottom have you?

Nope, that was the first conclusion I jumped to!

I had a similar problem when I replaced a Stronglight 1" threadless headset with a Cane Creek Series 40 1" one. The steerer (alloy fork with pseudo-aero blades) passed through the top cup but not the bottom one. Ended up pairing the top cup of the Cane Creek with the bottom cup of the Stronglight. Looks slightly goofy, but then so does the rest of the bike.

could be a JIS/ISO incompatibility.

JIS headsets: crown race ID - 27.0mm; cup OD - 30.0mm

ISO headsets: crown race ID - 26.4mm; cup OD - 30.2mm

and these are interference fit, so pressing type force is expected

On closer inspection, Ribble appear to have sent me the wrong headset: a CC 40 EC30.

Think this might be why?