If the piston is in the bottom of the stroke, the exhaust port is open to the exhaust chamber. At some of the shorter/steeper boat ramps, i.e. the Keys, the angle of launch is such that the stern of the boat goes deep before it begins to float off the trailer. This dunks the engines momentarily so the lower cowl, and even the engine engine cover itself, goes underwater until bouyancy is achieved. This puts the #5 cylinder, the lowest of both cylinder banks, lower than the water level allowing the water back-filling into the exhaust chamber to then enter the cylinder via to open exhaust port. Corrosion sets in and the rod bearing evetually fails, resulting in said catastophic failure. I now launch with the engines trimmed up to prevent this.
Backing down in a following sea, the kind that makes you take some water through the transom door, can also cause this if one of the engines is off. I knew about this possibility and always trolled with both engines on, so the exhaust pressure would prevent this. I don't know if the previous owner, who was a Yamaha-sponsored SKA angler, may have trolled with only one engine started in an attempt to conserve fuel.
That's what the mechanic told me and I've got several confirmations on the FS website. I was real careful launching today.
Let me get the break-in completed and we'll get toigether for some sailfish action this winter or get the dolphin in the spring-summer. It is indeed good to be back in the saddle, albeit somewhat costly.
