Premature impeller failure cause
I repowered my Cape Dory MS 300 back in the winter of 2008-2009. At the end of the first season going from a Westerbeke 46 to a Westerbeke 55. Had an impeller failure at the end of the summer in 2009. The blades of the failed impeller were fine, but the brass fitting/bushing and key pin had delaminated from the rubber bushing. This happend with about 100 hours on the engine.
Last week upon starting the engine I noticed that the burbs of water from the exhaust were much less frequent than normal (15 to 30 sec intervals vs the normal 5 to 8 sec). Turned out that the impeller agained failed in the same manner. It was probably still spinning somewhat providing a little water to the pump and exhaust.
The first impeller was branded as a Westerbeke, the second as a Johnson. Don't know if they are made by the same manufacturer or not. Any thoughts on what the cause may be? My mechanic thinks it could be that the thru-hull and seacock fitting might be undersized for the new engine. I think the thru hull is 3/4" with a 5/8" hose fitting. I looked through the engine manual and installation guide and didn't see a a minimum size for the thru hull. I'm going to call Westerbeke and or Hansen Marine (the Westerbeke dealer) also to see what they think.
Sort of an aside, but I was surprised that the impeller for the new 55 hp engine was much smaller than the one on the old 46 hp. Any ideas will be appreciated.