Internal combustion powered tool for driving fastening elements

Portable, internal combustion power operated setting tool for driving fastening elements into a receiving material, comprising a housing (2, 3), an axially extending combustion chamber (9) within said housing, an axially extending piston (7, 7a) guided within an axially extending guide chamber (8) and at least an axially extending part of said guide chamber being mounted within said combustion chamber and being axially displaceable therefrom, said piston can be driven axially within said guide chamber by gas pressure generated by the combustion of an air-fuel mixture within said combustion chamber, and means connected to said combustion chamber for preparing the air-fuel mixture, wherein the improvement comprises that said combustion chamber is defined by an axially extending cylindrical housing, said combustion chamber housing has a rearward end and a forward end spaced apart in the axial direction, means within said combustion chamber for varying the combustion chamber volume including at least one combustion chamber wall (11) located within said extending transversely of and displaceable in the axial direction of said combustion chamber housing, said at least one combustion chamber wall (11) being axially displaceable within said combustion chamber housing between a non-operating condition adjacent the rearward end of the combustion chamber housing and an operating condition adjacent the forward end of the combustion chamber housing, said at least one combustion chamber wall (11) arranged to receive and readably hold said piston (7, 7a), a metering chamber (67) located within said housing for supplying a predetermined quantity of fuel, first means within said housing and in communication with said combustion chamber for supplying air and gaseous fuel into said combustion chamber, and the air-fuel mixture are drawn into the combustion chamber by increasing the combustion chamber volume and establishing a negative pressure therein.