Re: Premature impeller failure cause
I am beginning to suspect a product failure if you have followed the installation steps I discussed. Replace the impeller with Westerbeke parts. All I use are Yanmar direct parts - no aftermarket. Replace every 12 mos or 100 hours.
Replace your impeller as I described. Give her a good run for some hours. Open is and take a look at the impeller. Also, at 55ish HP, you should put out about 5 gallons of water/minute from the exhaust. Stick a bucket under there and see what you get. THat is what the specs are for Yanmar anyways, IIRC. CHeck out the amount with Westerbeke.
Hope these suggestions help. ALso, make sure your hose is not collapsing under higher rpms (from Thull/strainer to block).
Called Hansen Marine (where I got the engine) this morning. They were saying the thru hull should be 1". I think I have a 3/4" with a smaller hose fitting attached. (being 450 mi from the boat I cant check right now) I'm goung to check with Westerbeke directly also. Can't find a specification in the installation guide or manual.
Thanks for the help. The Hansen guy thinks that the impeller is having to work too hard to get water causing the delamination.