Just fitted some forks to a frame & without any spacers the gap from the top of the stem to the top of the steerer tube is 6mm.
I know 3mm is recommended, will 6mm be OK?

assuming you mean the top of the steerer is 6mm below the top of the stem then I wouldnt risk it.
It really needs to be clearly above the top of the top bolt hence the 3mm recommendation.
The risk if this critical part fails is pretty nasty….not worth it IMHO.

Lower stack height stem or even a single bolt stem may be the answer.

If this is with a certain frame <ahem> and you don’t feel you can run with a 6mm gap, I have a headset that could help you out. What stack height is the stem? Some FSA stems will shave off 5mm over the usual 40mm jobs.

Yep, thats right – what headset?
If the CK headset sat closer to the fork crown it would be fine but the crown race is thick so the lower cup is a good 2-3 from the fork.
Would like to keep the Thomson or Ritchey WCS stem, both 40mm.

There’s a chance you’ll crimp and weaken the steerer as the top bolt(assuming its a 2 bolt stem) isn’t tightening down on tube correctly. Lower stack headset or stem might sort it.

Nice to keep the CK headset on it but could help in either of two ways: CB headset (21mm stack) or, depending on the length you need, a FSA stem. Obviously done at a very-patient-buyer rate 😉

IMO 6 mm is fine – so long as the steerer is above the top stem bolt

I need to loose 3mm, so the CK is listed as 31mm so need 28mm or less.
Just bought a Crank Bros due to same problem on a winter SS frame but it seems a bit low quality – very sensative to amount of preload to whether it turns freely or not.

The top of the stem to the centre of the top bolt is 7mm on my Ritchey WCS stem. 6mm on the Thomson.

Might just order a CB headset. I’m assuming the CB headset with the most balls per race is the best, Opium DH 34/34?
The CB Cobalts or Iodine have 28/28 or 28/34.

File the top of the stem. 🙂

XLII is about 28mm…probably more reliable than the CB headset but closer to your limit. I’ve a fitted once but unused XLII…I have an embarrassing amount of bike bits that I really should flog on 😳

Alternative to the CB headsets is the Across (Balfa bring them into the UK). Typical headsets have a c31mm stack height. CB are 21. Across comes in at 24mm I think. Lightweight and look built to last.

Very unimpressed by CB headsets, completely dead in under a year. If you only need 3mm buy a lower stack stem instead

Sunline V1 All Mountain stems have a 34mm stack height, i’d be looking at something like that and keeping the king. CB stuff is chocolate.. lots of folk have reported very early corrosion issues with their Headsets.

Quit stressing~ if you use the ritchey stem, you’ve got a whole mm of insurance 😉 … unless its a carbon steerer

as anc says, the Sunline V1 has quite a low stack height. Quite a nice little stem too. I’m happy with mine. It’ll give you a few more mm to play with.