Manual - Chapter 4 - Cooling

9. Water pump: removal, renovation and refitting

  1. To prevent leakage of water or oil from the cooling system to the lubrication system and vice versa, two seals are fitted on the pump shaft. The seal on the water pump side is of the mechanical type having a spring loaded annular face which bears against the rear face of the impeller. The second seal, which is mounted behind the mechanical seal, is of the normal 'feathered' lip type. Both seals area drive fit in the pump body.
  2. Where work on the seals is required, the pump must be removed first, as follows.
  3. Drain the coolant. See Section 2. Drain the engine oil, as described in Routine Maintenance. Disconnect the oil pressure switch lead and remove the radiator bottom hose
  4. Remove the pump front cover retaining screws and withdraw the cover then remove the pump body retaining screws and withdraw the pump body; a few gentle taps with a soft-faced mallet should break the joint seal.

    Note: the 0-ring sealing the coolant passage between the pump and the crankcase lower section, also the 0-ring around the pump drive shaft rear end; both of these should be renewed whenever they are disturbed.

  5. Remove the pump drive gear and insert a 6 mm Allen key into the pump shaft rear end. Clamp the key in a vice to hold the pump shaft and unscrew the impeller retaining nut (early models) or bolt (later models). Using a soft-faced mallet, or a hammer and a wooden or soft metal drift, tap the pump shaft out of the impeller, then withdraw the impeller and shaft.
  6. Taking care not to scratch or damage the pump body, pull or lever the mechanical seal out of its housing and use a slim (5 mm/0.20 in blade width) screwdriver to drive out the rear seal working from the pump's rear face.
  7. Carefully clean all components and check those of the oil pump for wear; see Chapter 5 - section 23 Oil pump: removal, examination and refitting. Renew both seals whenever they are disturbed, also the 0-rings.
  8. On reassembly, fit first the rear seal, with its manufacturer's marks or numbers facing forwards, using a hammer and a tubular drift such as a socket spanner which bears only on the seal hard outer edge. Drive the seal in until it seats against its locating shoulder. A smear of grease around its outside edge will help the procedure.
  9. The mechanical seal is fitted in the same way, using a 22 mm socket spanner and 1 /2 inch drive to drive it in until it seats. However, it must be kept completely free from grease and must be washed in a methylated spirit/water mixture to degrease it before installation
  10. Insert the pump shaft into the rear of the pump body. The mechanical seal centre is a very tight fit on the pump shaft; to refit the shaft rest its rear end against the work surface, apply both thumbs to the mechanical seal centre and press the seal (and pump body) over the shaft end.
  11. Tighten the impeller retaining nut or bolt to its specified torque setting then refit the pump drive shaft with a new 0-ring. Installing an 0-ring around the coolant passage, apply a thin smear of Three Bond 1207 B sealant to the pump/crankcase mating surfaces and refit the pump ensuring that the drive shaft engages correctly in the output shaft.
  12. Rotate the crankshaft to centralise the pump gears while tightening the pump body mounting screws to the specified torque setting (where given). Connect the oil pressure switch lead to the switch terminal and carefully refit the switch cover. Apply a thin smear of Three Bond 1207 B sealant to the mating surfaces and refit the pump front cover, tightening its retaining screws to the specified torque setting, where given.
  13. Fill the cooling system again. See Section 4. Refill the engine with oil as described in Routine Maintenance. Refit all other disturbed components.
  14. In the event of seal failure, the inter-mixing of oil and water in the engine will cause sludge to form. The extent of sludging will depend on the quantity of contaminant and the length of time during which contamination has taken place. Before the machine is returned to service, when new coolant and lubricant should be used as a matter of course, it is strongly recommended that the engine be flushed out thoroughly using a proprietary flushing oil. Furthermore, where extensive contamination is evident, an additional oil change is recommended approximately 500 miles after seal renewal. It should be noted that the presence of water in the lubricating oil will reduce its lubricating properties dramatically and may cause permanent damage.

9.3 Remove bottom hose prior to oil/water pump removal

9.4a Remove pump front cover retaining screws...

9.4b expose pump body mounting screws

9.5a Use an Allen key to hold the pump shaft when slackening impeller nut or bolt

9.5b Remove impeller to release pump shaft

9.6 Pump mechanical seal is fitted behind impeller

9.11 Always renew O-ring around coolant passage