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just bought a all carbon fork (carbon steerer too)
the top of the steerer is flush with the top of my stem (with no room for spacers)
I have ordered a long 50mm carbon steerer bung
how can I preload the headset now if everything is flush?
is it safe to put a 3mm spacer (and rest it ontop of the stem) then bolt it down?
3mm spacer under the stem? Or, cut 3mm from the steerer tube?
[i]is it safe to put a 3mm spacer (and rest it ontop of the stem) then bolt it down? [/i]
yep.
I'd put a 5mm one as you'll find the steerer will 'rise' out of the top of the stem as you tighten the top cap.
Once the stem is tightened the top cap bolt doesn't do anythign anyway so you just need the clearance to do the pre-load properly.
[edit] as per your previous post - you shpoudl always have spacer on top of the stem with a carbon steerer anyway so thet the stem clamps properly on the carbon tube.
I was worried about 'pinching' or cracking the carbon steerer at the top (if the steerer & stem wasn't flush)
ideally 3mm would protrude over the stem and I'd place a 5mm spacer over it.
[i]ideally 3mm would pertrude over the stem and I'd place a 5mm spacer over it. [/i]
you need more than 2mm of gap between top of steerer and top of the spacer os if you have 3mm past the top of the stem use a 8mm spacer.
as long as the steerer is out the top of the stem when it's all tightened up and you use a torque wrench/don't swing on the end of an allen key on the stem bolts you'll be fine.
You're better off with a small spacer above the steerer anyway - so you're clamping the entire stem on the steerer. It's a stipulation with certain carbon steerers.
if spacer is just resting ontop I was worried it would lead to problems if it wasn't aligned or got a knock?
Put the stem on in the desired position, then put a 3mm spacer resting on top, then the top cap. As long as your bolt is long enough it will preload the headset without any issues. Once the stem bolts are tight, remove the spacer and tighten the top cap down loosely.
Once the headset is preloaded the top cap serves no purpose apart stopping it look daft and mud getting down there
2mm looks better.
if it's flush now then the steerer will stick out the top of the stem a bit when you've finished.
once the stem bolts are tightened you can remove the top cap, bolt and spacer if you want - they only hold it together until the stem clamps it all up. I'd leave them on and there'll be a bit of steerer for them to 'rest' on - I wouln't worry.
It should be fine. The steerer will creep up past the stem when you tighten the top cap.
Spacer under the stem is another option
the best I can get then is
steerer dead flush with the top of stem
5mm spacer resting ontop of stem
50mm carbon fork expander bung
no spacers under stem