Jem, Just a couple of extra thoughts on this topic:- It is extremely important that, whatever you decide to build, you really want to build it because, in a project of this nature, there will be times when you are all by yourself and feeling that it will never be finished. At this point it is pure determination that keeps you going! A lack of such determination results in the engine joining the thousands of other part builts gathering dust under benches. On the subject of scale backheads. I think a truly scale backhead is a sight for sore eyes but, having driven a few, I can assure you that it is like putting your hand in wasp's nest! and that's with 5" gauge engines. Barrie MODEL ENGINEERING DISCUSSION LIST. To UNSUBSCRIBE from this list, send a blank email to, modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line.