How to Replace a Water Pump Seal on a CRF450

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The CRF450R was the second to the largest member of Honda's new-for-2002 CRF motocross-based off-road motorcycles, shadowed only by the CRF650. The CRF's four-stroke 449 cc single-cylinder engine was cooled by a dual-radiator cooling system, powered by a small water pump on the right side of the engine. While the physical demands of off-road racing could take a toll on the water pump, often leading to visible damage to the water pump's aluminum cover. However, less than obvious damage can occur to the water pump's internal seal that could result in failure of the water pump. Internal damage is often displayed as a small antifreeze leak emanating from a tiny hole -- called a telltale hole -- at the bottom of the water pump. If a leak has occurred, the water pump must be replaced.

Things You'll Need

  • Service stand
  • Drain pan
  • 10 mm socket
  • Socket wrench
  • Copper crush washer
  • Flat-head screwdriver
  • Water pump cover O-ring
  • Bypass pipe
  • Bypass pipe O-ring
  • Impeller
  • Impeller washer
  • Impeller shaft
  • Water seal
  • 12 mm bearing remover (Honda part No. 07936-166010A)
  • Bearing remover handle (Honda part No. 07936-3710100)
  • Bearing remover weight (Honda part No. 07936-3710120)
  • Water seal driver (Honda part No. 07965-415000A)
  • Bearing driver (Honda part No. 07749-001000)
  • 12 mm pilot (Honda part No. 07746-004020)
  • 17 mm open-end wrench
  • Torque wrench
  • Pro Honda HP Coolant or similar antifreeze
  • Distilled water
  • One-quart resealable plastic container
  • Triangular side stand
  • Mount the CRF450R on a service stand and let it cool for at least two hours.

  • Unscrew the filler cap from the top of the right radiator.

  • Place a drain pan below the water pump on the right side of the engine, identified by the coolant hose running from the top of the pump to the CRF450R's radiator. Loosen the drain bolt, located at the bottom of the water pump, using a 10 mm socket and a socket wrench. Unscrew the drain bolt and replace its copper crush washer. Let the coolant drain completely into the drain pan.

  • Loosen the coolant hose clamp at the top of the water pump, using a flat-head screwdriver. Pull the coolant hose off the water pump inlet. Unscrew the remaining three water pump bolts, using a 10 mm socket. Pull the water pump cover and O-ring off the right engine crankcase cover by hand.

  • Unscrew all 11 bolts from the perimeter of the right engine crankcase cover, using a 10 mm socket. Pull the crankcase cover and gasket off the engine. Pull the bypass pipe off the coolant inlet on the right side of the engine, located at the upper edge of the crankcase cover's mating surface, by hand.

  • Pull the O-ring off the bypass pipe. Inspect the bypass pipe for signs of damage, such as deep scoring, cracking or corrosion. Replace the bypass pipe if it is damaged in any way. Slide a new O-ring onto the bypass pipe, then push the bypass pipe into the crankcase.

  • Unscrew the water pump impeller from the right engine crankcase cover, using a 10 mm socket. Slide the impeller washer off the impeller shaft, then pull the impeller shaft out from the inside face of the cover. Inspect the shaft for signs of damage, such as any bending or wear. Replace the shaft, if needed.

  • Check the water pump seal, located directly under the impeller's mounting point on the right crankcase cover, for tears or puncture marks. The seal must be replaced if it is damaged in any way.

  • Spin the impeller shaft bearing race, located in the right engine crankcase cover, by hand. Ideally, the bearing should roll smoothly without binding. The bearings must be replaced if the bearings bind or feel notchy. Additionally, the race should not have any side-to-side or up-and-down play.

  • Insert a 12 mm bearing remover -- Honda part No. 07936-166010A -- into the impeller bearing from the inside of the right crankcase cover. Connect the bearing remover handle and bearing removal weight -- Honda part Nos. 07936-3710100 and 07936-3710120 -- to the bearing removal. Slide the bearing weight backward forcefully against the handle until the impeller bearing is removed completely from the crankcase cover. Pull the oil seal out of the crankcase cover.

  • Drive the water seal out from the outside of the crankcase cover, using a water seal driver -- Honda part No. 07965-415000A.

  • Drive a new bearing into the right crankcase cover, using a bearing driver and a 12 mm pilot -- Honda part Nos. 07749-001000 and 07746-0040200. Push the new oil seal into place through the front of the crankcase cover. Drive a new water seal into place over the oil seal, using the water seal driver.

  • Push the impeller shaft through the inside of the crankcase cover. Hold the shaft in place with a 17 mm open-end wrench. Slide the impeller washer over the shaft, then screw the impeller into place by hand. Tighten the impeller to 9 foot-pounds, using a torque wrench.

  • Reinstall the right crankcase cover and gasket onto the engine. Tighten the crankcase cover bolts to 7.6 foot-pounds. Reinstall the water pump cover and a new O-ring onto the right crankcase cover. Tighten the cover mounting bolts to 9 foot-pounds and the coolant drain bolt to 7 foot-pounds. Push the coolant hose over the inlet at the top of the water pump cover, then tighten the hose clamp.

  • Pour a half-quart of Pro Honda HP coolant or a similar silicate-free ethylene glycol antifreeze into a one-quart resealable plastic container, followed by a half-quart of distilled water. Seal the container and shake thoroughly to blend the antifreeze solution.

  • Fill the right radiator through its filler neck with the antifreeze solution. Remove the CRF450R from the service stand, then slowly lean the motorcycle from side to side to remove any air bubbles trapped in the radiators. Add more antifreeze if the antifreeze level decreases after bleeding out the air bubbles from the radiator. Screw the filler cap into place.

  • Mount the CRF450R on a triangular side stand for storage.

  • Transfer the old antifreeze from the drain pan to the container used to mix the new antifreeze solution. Take the antifreeze to an automotive fluid recycling center for disposal.

Tips & Warnings

  • Antifreeze contains ethylene glycol alcohol and can cause serious illness if swallowed or ingested. Store the used antifreeze in a sealed container, away from the reach of children or animals, if you cannot dispose of it immediately.

References

  • 2003 Honda CRF450R Service Manual; Honda Motor Company
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