Abstract: A diesel-engine pile driving hammer provided with interchangeable rams for use in a single, outer, cylindrical casing. A large diameter hole or orifice is provided in the casing between a pair of an array of alternate orifices which are capable of being plugged. The larger orifice or alternate orifices provide an air inlet-exhaust port or ports of sufficient dimension to enable all of the exhaust gases of combustion to be expelled in the time it takes a ram of designated weight to travel its upward stroke in the casing and to vary the swept volume of air introduced into the combustion chamber in the casing so that different weight, interchangeable rams may be accomodated in the same outer cylindrical casing to obtain prescribed impact energy values.