waterpump and fan?

How does a bad waterpump cause the radiator fan blades to break off?
97 328iC Automatic 115K

2 months ago I got my waterpump replaced. Next thing I know is that my fan blades broke off. Then I got a new fan and fan clutch.

Last week fan broke again... Took it to a BMW speacialist. They said the engine mounts looked fine.

They changed the waterpump, fan, shroud, radiator. Note all oem parts.

The old waterpump (2 months old) the metal impeller does not spin around freely, it seems as it broke. Note it was an aftermarket part.

My question is... can a bad waterpump cause the fan blades to shear off???

What can cause a new waterpump to fail or to be destroyed?

Can this bad waterpump be taken back to the parts store, i've got all my receipts... and will they be responsible for the fan...etc?

Thanks for your input.

There is a hose in the top of the radiator shroud that snakes around to the coolant reservore.It is heald in place by two plastic tabs on the shroud.If they are broken off or if the hose was installed wrong the fan may hit the hose. And it my only do it when the car is going fast enough to cause the blades to flex.

when the water pump bearing fails it causes the wobel in the pully witch is transfered to the fan blades and if water pump pully is moving in and out bad enough the fan can hit stuff or if it fails all together the belt can come off and damage the fan.