B series water pumps – Which one?

MGA, MGB 3 main bearing, and MGB 5 main bearing engines all had different water pumps.  MGB 5 bearing engines also had two types of water pump, differing in their length.

When ordering replacements, it helps to check which pump type you have, since with the passage of time the original pump may have been changed to another type.

To check the pump type:

MGA pump (GWP103) and 3 main bearing MGB pump (GWP115) have a smaller (60.3mm) impeller.

The earlier 5 bearing pump (GWP114) fitted on enignes 18GB to 18GG had the steel fan with no spacer between fan and the pulley.

The later 5 bearing pumps (GWP130) can be identified by the presence of a spacer approx 20-25mm thick between the pulley & the original 3 bladed steel fan, or by the presence of a 7 bladed plastic fan.

Other applications: 

Obviously, this range of pumps was used on contemporary BMC B series engines.  The MGA pump GWP103 also does all B series 1500 and 1622cc engines other than vans/commercials produced in the late ’60’s and ’70’s.  These engines had the 5 main gearing type of pump.

5 bearing pumps: GWP114 was used in the BMC 1800 and GWP 130 was used in the Marina 1800.

The following photos show the detail differences between the various pumps:

MGA pump:

Paul Walbran Motors

MGA pump has same 60.3mm impeller diameter as 3 brg B but different bolt pattern

Paul Walbran Motors

Length of MGA pump

MGB Pumps:

Paul Walbran Motors

3 main bearing pump (top) has smaller impeller,GWP114 (lower left) is longer than GWP130 (right)

Paul Walbran Motors

Impeller diameter and gasket face of GWP115, fitted to 3 main bearing MGB

Paul Walbran Motors

Length of GWP115 (3 main brg pump, 1962-64) is the same as that of GWP114

Paul Walbran Motors

Length of GWP114, originally fitted 1965 to 1971

Paul Walbran Motors

Impeller size, GWP114 or GWP130 (bottom) – larger than GWP115 or GWP103 (top)

Paul Walbran Motors

Length of late MGB 5 brg pump GWP130, originally fitted 1972 on

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