an electric motor and reduction gears not shown enclosed in a housing 14 the housing 14 typically includes a flanged head 15 bolted thereto by bolts 17 to convert rotating action of the drive a into the reciprocating action of the pump c the linkage b includes a crankshaft 16 connected at a one end to the drive wheel 12 by a first pin 18 at the other end the crankshaft 16 is pivotably connected to a crosshead 20 by a second pin 22 the crosshead 20 slides reciprocally within parallel guides 24 integral with the housing 14 the crosshead 20 includes an outer distal surface 26 suitable for the connection of a crosshead extension rod 28 while any connecting means can be employed the crosshead extension rod 28 is preferably connected to the crosshead 20 by flange 30 formed at a proximal end 31 thereof the flange 30 is bolted at the crosshead surface 26 by bolts 32 the crosshead extension rod 28 includes a distal end 34 received in an opening 36 in the drive housing 14 and extending into the pump unit b the opening 36 is preferably sealed by a bushing seal 37 to inhibit flow of lubrication fluid from the drive housing 14 to the pump unit b the distal end 34 of the crosshead extension rod.