Basics Steps For WR400F Water Pump Rebuild

Drain coolant, remove front exhaust, (if exhaust has dents, this would be a good time to fill with water and place in freezer). If you don’t want to drain oil, then lean bike on left side. Remove: kick start lever, brake pedal, 2 oil line bolts on side cover, coolant hose on side cover, water pump cover. Use a 12 mm socket to remove impeller (put engine in gear and lightly tap on wrench). Remove 8 mm bolts holding side, 1 lower bolt on oil filter cover and 2 upper clutch cover bolts (the ones that go into engine case; complete clutch cover removal is unnecessary), remove side cover (if the gasket is not damaged it can be reused), remove water pump shaft, pry out water seal (note spring side faces out toward impeller), use socket and tap against oil seal to remove seal and bearing (note spring side faces in toward engine/bearing).

Check shaft for grooves and replace if necessary, mine only had cosmetic blemishes and looked bad until I cleaned it up with emery cloth (and this was after 9 years of significant use) Check bearing and replace if needed; mine was good.

Press in new seals using a socket if needed, make sure to grease the lips, tap in the bearing with socket.

Reverse the removal steps, make sure the pump shaft is aligned with the slot when installing the side cover.


Thank for the info. I am just about ready to tackle a water pump replacement on my 426. This surely helps.

Thanks again.

Really appreciate the information.

My WR400f started leaking water badly. I changed the water pump seal and as the pump shaft was in good condition did not repalce.

It leaked just as bad.

On reading the information on the forum I realised the guy who owned it before me had fitted the seal back to front.

I refitted it new seal correctly and no issues.

reading this forum saved me replacing pump shaft and a lot more money and still have the problem

Big thanks

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