"Everyman's Jet Engine" - Why Valveless Pulsejets? No replaceable parts except fuel nozzle (and optionally, spark plug) Strictly speaking, because we have no internal movable parts, we could build our engines with no parts capable of being removed and replaced. However, I would advise against this -- there are a couple of parts that deserve to be made easily replaceable. The fuel nozzle, at least in the case of liquid fuel engines, should be set up so it can be removed and cleaned (or replaced) if it ever becomes clogged or damaged during use. Another reason is that, even when we have a well-tuned engine that runs well, the fuel nozzle is one of the most interesting things to change experimentally! I have seen hobbyists actually weld a sparkplug into the chamber; but, if such an engine is dropped and the plug insulator broken, replacing it will take time-consuming (and very careful) effort. Simply being able to thread the old one out and replace it in five minutes makes a lot more sense to me!