Mariner 2HP Outboard
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Yamaha 2.5hp Outboard Service Manual

Mariner Water Pump Refurbishment

The water pump of the Mariner 2HP is housed in the lower, gearbox, casting of the outboard. Obtain the Yamaha water pump service kit Part number 6A1-W0078-01. Also ask for a second seal, for the lower water pump (It is exactly the same as the one in the kit). The job takes about three hours when all the tools are to hand.

To gain access to the pump impeller and pump body follow the steps:

  1. Remove the propeller taking care not to loose the drive pin.
  2. Locate the lower casting and remove the two 10mm bolts, one located on the upper side front and the other on the lower side, just above the propeller boss.
  3. Gently but firmly ease the gearbox complete with water pump and any internal pipes from the outboard leg. This usually requires two levers applied on opposite sides. The pressure should be applied evenly and the gap must be kept parallel to avoid damage to the casting
  4. Remove the two bolts securing the gearbox faceplate and gently but firmly remove the faceplate. If the propeller shaft is kept pointing up during this operation then the oil will be retained in the gear casing.
  5. Once the faceplate is removed, drain the oil and then carefully remove the circlip from the end of the drive pinion.
  6. Once the lower housing is removed the two 8mm bolts securing the water pump upper housing may be removed and the water pump impeller is accessible. Now carefully withdraw the drive shaft noting the position of the pinion and thrust washers positioned on the drive shaft immediately behind the pinion. Also be careful not to loose the impeller drive pin located in the drive shaft just below the water pump upper housing. Remove the impeller.
  7. Disassemble the drive shaft tube from the pump upper body together with the drive shaft. This may prove to be quite a difficult task as the tube is quite thin walled and can be corroded into the pump housing. Be patiently persistent!
8. The stainless steel pump liner can be removed using a gaz torch to carefully heat the area whilst prising out the body and plastic seating. Remove the rubber seal. 9. Clean the seal housing and replace the seal. Apply grease to the seal and a liberal coating of yellow chromate 'Duralac' to the cleaned pump casting.
10. Align and assemble the SS pump lining into the plastic liner and, taking care to align everything correctly, position these components into the casting. Clear surplus material from all outlets.
11. Carefully clean the casting and replace the seal, 'O'Ring and outlet grommet. Careful not to loose the two locator lugs. NOTE: The seal is not part of the service kit so make sure you obtain one at the time you purchase the pump service kit. Ensure the faceplate is clean. Carefully offer up the drive shaft through the seal.
12. Fit the drive shaft cover tube, using a little MS4 silicone grease. Coat the faceplate of the housing with yellow chromate and place the S.S. pump top plate in position. Locate the impeller drive pin and refit the impeller. Now to assemble the pump and gears.

13. Locate the drive shaft into the lower housing and slowly bring the two halves together until the thrust washers and pinion drive can be assembled onto the end of the drive shaft. Refit the circlip. Refit the gearbox faceplate, renewing the 'O' Ring as required, and refill the gear oil.

14. Carefully bring together the two parts of the outboard (I coated the mating surfaces with yellow chromate prior to assembly) ensuring that the drive tube and water cooling pipe locate correctly in the appropriate grommets. Tighten the two 10mm bolts evenly. I ran the engine at this stage, without the prop, in a large bucket. Once tested, the propeller can be mounted and the engine put back into service.

Do not run the engine dry as this will quickly damage the impeller and cause unnecessary pump wear.

This page was last updated on Tuesday, September 18, 2018 11:05 by Richard Spencer.