Water pump - large cast impellor with bypass and gasket.
Large impeller higher capacity water pump with a high quality die cast body.
Fitted with a PPS, glass filled plastic impeller as used by Aston Martin and Jaguar it reduces weight on the bearing loading and has a triple lip seal giving a better controlled flow rate through the rev range. The pump is about 130 grams lighter and has the rolled edge gasket facing evolved by Rover for better sealing. Tested with coolant pumping at 10,000 rpm with no detriment to the PPS impeller this larger impeller pump moved more coolant than the original early GWP132 standard pump.
GWP134EVO has by-pass hose take off and see GWP187EVO without take off. These water pumps have a much larger impeller, it sticks into the block very slightly more than 1/2"(14.03mm).
This water pump will fit all 1275cc blocks and all small bore blocks, with the exception of early 850/997cc units. These early blocks will need an amount of modification, relieving corrosion and slight material from the liner wall and impeller if required should enable clearance, try spinning pump loosely fitted without gasket for clearance. The high capacity water pump helps to reduce cavitation in the water jacket, particularly at high RPM, as well as circulating a greater volume of coolant. Further reduction of cavitation is achieved by using a large diameter water pump pulley CAM6408 as originally fitted to the Cooper S and reintroduced on the A-Plus engines. It is necessary to check clearance between the large pulley and the head, if a lot of material has been machined from the head face it may foul the pulley.
Small bore engines with 12G940 heads can't use CAM6408 and it is necessary to modify the top edge of the high capacity water pump or the 12G940 head will rest on the pump and not seal properly, modify for at least a 1/16" gap.
Use SH605101 x2 and BH605151 x2 bolts.