Hello everyone, Dunc 333 has me to post some pics and give an overview and background of what happened. 1999 Yamaha CV75, (75A in the USA I believe) I've had since new. Yearly service by Yamaha reps in Sydney and flushed after use for 5 - 10 minutes. Usually within an hour after use. A couple of minutes at idle then 3000rpm then back to idle and unplug fuel line until fuel runs out.
Generally running for 2 - 3 hrs on Sydney Harbour at least once a month. I drift fish so motor is stopping and starting maybe 20 times a trip.
Occasional outside trips which usually involve trolling at 5-7 knots for several hours at 1500>2000 rpm.
Boat was serviced in July 2017. Invoice states pump parts, spark plugs, gear plug washers and 2 throttle washers that were sticking.
Fished at the end of July and boat did not go back in the water until mid October for various reasons. Boat was trailered 150km each way to Shoalhaven Heads. Unfortunately I encountered a sand bank on this trip but boat ran well after this with no issues.
Next trip was January 2018 when the incident happened. Boat was checked and prepped the day before. Both son and I commented on the strength of the tell tale and how easily the motor started.
Was the tell tale working at the ramp? I can't say for sure. (My bad).
15 to 20 minute run at 3500rpm then down to 2500rpm for 15 knot zone for maybe 5 minutes. Coming out of the zone we sped up to 3500rpm and the motor over revved. I thought we may have hit some weird cavitation or worse - dropped a blade or even the whole prop.
Pulled back the throttle and went to go again and motor over revved and heat alarm went off.
Shut down and checked for blockages or line tangles with nothing obvious.
Went to try again and alarm was still there and noticed no tell tale. Called a mate and got towed back in.
Back home tried a few things then pulled the exhaust covers off. Son found a piece of metal. There was also some salt build up with bits of grit in some areas and the area where we found the key had rust stains around it........
A few days later his mate who is a marine mechanic came around to have a look and I showed him the bit of metal.
"Woodruff key - there's your problem". Pointed to where we'd found it which he thought was most unusual and he seemed to think we'd find another key. Took bottom of leg off but could not find another key. He thought the key was slightly worn but still serviceable. Impeller looked like new but the white plastic housing was slightly distorted and discoloured which he attributed to the heat. Put the old key back in and away she went! Ordered new parts.
I'm slightly mechanical having worked on surface mount robots for 26 years but I'm no marine guru. BUT - I can't see how that key got there.
Her's the pics where you can see the rust stains showing where we found the key.
I'm waiting for the parts and we'll reassemble. Having cleaned the covers some of the interior paint has been abraded away - does anyone think this will be a problem?
Cheers DJOZ