I recently bought a 2001 310 Sundancer....

[Genny]

I recently bought a 2001 310 Sundancer. Once in awhile the port engine(350 MAG) raw water pump impeller vanes flip backwards when the engine stalls... this causes the belt to fry on the pump pulley because the pump won't turn.

    What would cause this...and more importantly, how do I remediate this. For now, I just turn the pump from the shaft with a pair of vise grips,, and off we go.???

[wingless]

Wow!

For the operational engine to stall, then to rotate backwards enough to flip some impeller vanes, then something substantial needs to obstruct the rotating / moving mass, causing it to bounce.

This is a serious problem.

Start w/ disassembling the elbow from the riser for an inspection of the internal raw water passages for corrosion and for inspection of the SOLID wall thickness of the raw water passages from the exhaust gas passages.

If bad, then also remove the exhaust manifolds and inspect the engine exhaust ports. If internal corrosion exists then it might be possible to extend the engine life by spark plug removal, followed by oil added and rotating the engine.

[wildog]

This is your problem each u-pipe where the water and exhaust go .has a flapper valve . This is a devise that lets water out with the exhaust . They are made out of plastic or aluminum clad in plastic they are an oval egg shaped insert that lay on top what about a quarter-inch into the exhaust pipe . The purpose of this device is to let water out and not let water run back into your Boat risers elbow and Manifolds this would be secondary to the walls between the exhaust in the water jackets in your manifold and or rises good luck been there done that