Abstract: An air starter includes a housing having a rotatable shaft extending longitudinally thereof. A gear is connected in a longitudinally extending helical groove on the shaft so that when the gear is moved along the shaft it engages an engine flywheel whereby the flywheel may be rotated by an air motor connected to the shaft. Piston means surround the shaft and sealably and slidably engage within a cylinder formed in the housing and the housing is provided with inlet and exhaust air passages for conducting air to the cylinder and discharging air therefrom. First spring means abut the piston means and the housing to urge the piston means to a first position in the housing. Annular means extend into the helical groove on the shaft and is arranged to rotate with the gear, therebeing second spring means between the gear and said annular means to retain said annular means disengaged from the gear when the piston means is in the first position.