Thanks Warren.

There are two types of filler necks that I am considering, one type is a length of aluminium tube with a thread cut on one end to accept the cap:



This type I would cut to length and may consider adding a knurl to provide keying where it locates in to the carbon part, providing that I cure the composite with the filler neck in place. If I bond it in after the cure I will probably just rough it up with some 80 grit or similar to provide keying but keep the part smooth for better location.

the other type is shorter and has a flange for mounting:



This type I would only really consider fitting pre cure and laminate the whole thing in to place

The easiest way would generally be to bond it into place from underneath.  You could certainly laminate over the base of the neck to give extra security to it. 

Alternatively if you can find a carbon tube of the right size, you could use a small section of carbon tube with a threaded insert bonded into it to accept the oil cap. With it being a carbon tube, you can make it more of a "feature" rather than something added on.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

I've been toying with the idea of making a carbon fibre rocker cover for my A series engine, the main body should be easy enough, but I'm a bit stuck on what to do for a filler neck. I think trying to produce a neck from composite would be difficult to do & potentially be quite weak, so this leaves me with the option of using an off the shelf aluminum weld on filler neck.