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RMA/E and RMB Water Pumps

Apart from  their main pump housings and their pulleys, the RMA/E and RMB pumps are virtually identical.  The RMB one with its double pulley is shown below in cut away form.  Two types of seal were used to prevent water from the main pump body getting into the bearings.  The earlier one is shown in the main illustration and the later one is shown in the inset.    The RMA/E pump is shown in exploded form in the second illustration and the later seal arrangement is shown at the bottom.

RM water pumps are generally very reliable and will run for a long time with minimal  servicing.  Water leaks, play in the bearings or bearing noise indicate that the pump should be removed, checked and serviced as necessary.  Pump removal is quite simple.  On an RMA/RME first remove the four screws holding the fan blades to the pulley and lift them away.  Remove the fan belt or in the case of the RMB, both fan belts.  Undo the four set screws just behind the pulley which hold the bearing housing to the main body.  One of these may be difficult to reach with a straight spanner and one which has been bent will make this much easier.  With all four screws undone, pull the bearing housing forward and lift it away.

Both pump designs have a sealing plates which fit into recesses in the main pump body and the bearing housing.  The bearing shaft passes through these plates with the impeller being attached to the rear end of the shaft.  In the earlier pump the shaft water seal is a ring of carbon which rotates with the shaft being driven by a peg through the shaft. The carbon seal is pushed against the sealing plate by a sealing gland and a spring the other end of which presses against the impellor.  In the later design the carbon seal is encased in a rubber housing which also contains the spring.  The rubber housing is a push fit into the sealing plate and the carbon seal which does not rotate pushes against the impeller to give a water seal. 

To dismantle the pump assembly, remove the nut holding the impeller onto the shaft and pull the impeller off the shaft taking care not to damage it.  Lift out the Woodruff key which drives the impeller from the shaft.  Remove the seal components.  Carefully remove the seal plate.  The seal plate in the earlier design can easily be broken so treat it carefully.  Turning to the front end of the assembly, remove the nut holding the pulley onto the shaft and pull off the pulley.  They pulley is keyed to the shaft with another Woodruff key.  There should be a felt washer behind the pulley which may remain stuck to the pulley.  If not, lift it away.  The shaft can now be pushed back out of the housing taking with it the rear oil seal, packing ring, rear ball race, distance tube and the inner race of the front bearing.  As original the front bearing is a roller race and the out track will remain in the bearing housing as the other components are withdraw.  It is possible that the pump has been rebuilt at some time and the front bearing may have been replaced with a normal ball race.

With everything dismantled clean all the components thoroughly and check them for damage and wear.  If parts need to be replaced they can be bought individually or as a complete kit.

If the carbon seal is being replaced on the later design check that the new seal is a good fit against the impeller face with a large area of contact.  It is possible to get seals where the hole in the middle is too large and the and the contact area is just a thin line around the edge of the impeller face.  Also squeeze the new seal between your fingers and check that the spring inside it is about the same stiffness as the one in the old seal.  A weak spring has been known to allow leakage past the seal at higher RPM.

New bearings may be of the “sealed for life” type and have inbuilt seals on either side.  Apart from keeping dirt out these seals also make it impossible to re-grease the bearings later.  This can be overcome by pulling off the forward facing seal from the rear bearing and the rearward facing seal from the front bearing.  When reassembling the pump place some grease in the space between the two bearings to form a reservoir of grease and this will keep them well lubricated for a very long time.  Do not completely fill the space with grease or it will try to force its way out through the bearings.

 Pump reassembly is a reverse of the disassembly procedure.  Note that the sealing between the main pump body and the bearing housing is done by the sealing plate and the recesses into which it fits.  A smear of sealing cement (e.g. silicon rubber) in these recesses will ensure that there are no leaks around the joint.  Note also that one of the lower screws holding the bearing housing to the main pump body breaks through into the water passage and therefore has a copper washer under it to prevent leakage of any water which may creep along the threads.