Reading the threads, I'm sold on the importance of using a reamer to clean carbon deposits, but I'm put off by the desribed cost of the reamer, a tool that I'd use once in forever. I'm gonna be pulling the glow plugs out related to tracing down a nailing noise.

The pictures in this thread nicely show a glow plug reamer is a very simple tool, that would seem to cost pennies to manufacture. (Thanks for the post with picture bodyart 27, it is the picture that is worth a thousand words that made me "get" what is being talked about in other threads.)

Is there something special like really fine tollerances, and dangers if you miss, that there is no discussion of a homemade tool for cleaning the carbon out of the glow plug area?