Abstract: In a Bourke type engine wherein at least two cylinders are disposed coaxially and oppositely so that the free ends of piston rods extending from pistons reciprocable in said cylinders may be connected by a yoke in coaxial alignment with each other and with the cylinders to reciprocate concurrently as a unit, with the yoke having means rotatably to engage a rotating crank by which the force developed by reciprocation of the pistons is converted to rotating driving motion, the improvements wherein the inner end of the piston rod is placed in abutment with the underside of the piston head and the yoke is modified to house a block slider instead of a rolling bearing to provide better bearing surfaces and lubrication thereof.