"Everyman's Jet Engine" - Why Valveless Pulsejets? Built without machining of any kind The total absence of internal moving parts means there are no sliding surfaces (i.e. "bearing surfaces") that require precision machining. Of course, it's true that most builders will want to mount a spark plug for engine starting; but for this, a steel or stainless nut matching the desired spark plug's thread can be used, by simply welding the nut onto a hole in the combustion chamber. A similar technique can be used in most cases to locate a fuel nozzle (or its mounting). While an engine must be built with reasonable "shop rule" accuracy, the demands of high precision machining are completely unnecessary.