I used to do a bit of casting as part of my "day job" in our family run jewellery workshop. Mainly using silver and gold I used a delft clay and some aluminium flasks to produce one off pieces that could be finished off by hand. I had some success with this process and found that it was great for reproducing detailed reproductions of existing pieces. The downsides of the method for producing bike related parts were mainly that you couldnt melt enough metal to pour the size of pieces I would want without having some sort of forge to get the metal (aluminium usuall) to 1340 deg to pour it successfully, and the 4" flasks were quite limiting!
I have been looking at the possibility of casting some of the hard to find pieces I need/want for my Indian projects, and found a couple of really informative sites
Lanstrom's Foundry Where the Warpath Indian cases are cast - awesome!
Backyard Metal Casting some great how to's and a whole lotta source info here
So I'm off into town on monday to buy me some fire cement and fireclay bricks! I'm gonna build me a forge ;-)