An injection pump for a diesel engine has a pump cylinder with a pump piston slideably mounted therein. The piston has a broadened foot portion. A cam is mounted on the camshaft and a rocker arm is mounted on a pivoting axis and has a camshaft end and a pump-side end. Means are provided for holding the camshaft end of the rocker arm in substantial contact with the cam. The pump-side end of the rocker arm has contact means for contacting the piston and moving the piston in the cylinder as the rocker arm is pivoted. The contact means includes means for loosely coupling the pump-side end of the rocker arm to the foot portion of the piston.