putting a new stem on a carbon steerer

[rollinstok]

Hi,
I,m slowly upgrading the bike and recently had fitted a carbon fork with a carbon steerer. There are spacers above and below the current stem which the mechanic said was kinder to the carbon. I am fitting a new stem soon and want to raise the bars by 5mm.. I can do this by shuffling the spacers about and there will still be a 10mm spacer above the stem ( a Ritchey pro ).
The new stem is a little taller than the FSA it is replacing but think I have the spacer sizes to sort it out.
Please can you help on a couple of possible issues...

How much of the top spacer should be standing proud of the steerer ?
I dont have a torque wrench and am worried about overtightening the stem on the carbon steerer..any advice ?
I believe the steerer has a special bung for carbon that the top cap fastens to.. is it a straightforward job to unscrew and replace cap without any issues ?

Sorry if the questions are a bit newbie.. its the first time I,ve worked with carbon and dont want to damage my lovely new fork. Any advice would be greatly appreciated.

 

[smokeysmoo]

My Cannondale has carbon forks and steerer, it's one of the few carbon parts left on the bike that I can't afford to change presently, (I don't like carbon TBH but that's just me). I actually don't have any spacers below the stem as I want to reduce the amount of stress being exerted on the steerer when I am out of the saddle. It may be me being paranoid, but if I can't relax when I ride I don't enjoy it.
Do your new forks need cutting down? If so put your spacers on to to the height you want your stem at, then remove one 5mm spacer, mark the steerer at that point and cut it, then when you replace everything the steerer will be the right length to secure the top cap. It sounds daunting but I did it myself for the first time last month with my new Ribble frame, and it's a doddle
I don't know if mine has a 'special bung' even though I've dropped the stem as low as it will go I simply re-used the top cap that came with the bike.
As for torque wrenches, some say they are not necessary and do it by feel, however, I'm a tad heavy handed TBH, so I invested in one and it's become one of my most used tools ever since. If in doubt loose fit everything then nip it to your LBS and ask them to torque everything up

 

[fossyant]

Blimey smokey, very paranoid. You need just about 1-2mm of excess spacer or stem above the steerer so that the top cap is only pre-loading the bearings, rather than tightening onto the stem. If you don't have the right amount of spacers, they are cheap.

Trek and one or two others recommend having a 2.5mm spacer or more above the stem - this means that the whole clamping area can evenly grip the steerer, rather than having 2mm or so at the top which might overstress the steerer. It basically means those that are a bit 'ham fisted' aren't going to do damage. This method also makes sense for alloy as well.

 

[smokeysmoo]

Blimey smokey, very paranoid.

I know

 

[baznav]

As long as you have got the carbon steerer bung you can't crush the steerer, realy dosn't matter where the spacers are.
However as some carbon steerer bungs may only insert about 30mm or so if you put all your spacers on top of the stem potentialy you are clamping your stem to an internally unsupported part of the steerer and crushing is verry possible.

 

[youngoldbloke]

+1 - however, longer bungs are increasingly available.