So if there's no drive shaft(you said no crankshaft) then it's of no use to us propel a vehicle????510Mods said:Thats truly not a "free piston engine" The pistons should not be connected by any-means to anything. And there is no drive shaft. A free piston motor is like 4 two stroke motors cradling 2 pistons. 1 chamber on each side of piston. Then in the very middle is and exhaust port with a special manifold chamber. But a true free-piston engine has only 2 moving parts. And also has 2 ignition sources, glow plugs for running and spark plugs to initial start. Which the starting is done by feeding it air pressure.