Abstract: A diesel fuel injection pump having a rotary fuel distributor head including a rotor disposed in very close clearance thereinside wherein a thermal shock barrier of an elastomeric material having a low thermal conductivity is disposed about the outside of the distributor head, the barrier having apertures through which the injection pipes pass. In its preferred form, the barrier is a one piece member fitting the distributor head beneath the injection pipe nuts. In an alternative form, the barrier comprises two pieces mating along the injection pipe apertures and enclosing the connections between the injection pipes and the distributor head. The barrier need not be waterproof but must be sufficiently protective of the distributor housing to prevent substantial amounts of water from contacting the distributor head.