A couple weeks back on a short run from dock my Model 6R69M suddenly quit with signs of overheating (engine quit, was very hot to touch and there was slight smoking around powerhead. I rowed home and tested in water tank. Engine was not making any "mist" (this engine has no peephole but has "mist" setudnp instead) indicating inadequate water flow. I removed thermostat cover and found extensive salt etc corrosion. I cleaned the thermostat cavity thoroughly but couldn't remove the cylinder head (one bolt/screw stuck) to do a deeper cleaning of the water jacket areas. I replace the thermostat and thermostat gasket/o-ring plus the thermostat cover gasket. Engine starts fine but still overheats. There is no mist coming out. I pushed a stiff wire up the mist hole and still no mist (I have found this technique often clears debris/buildup in peepholes).
So here is the question: should I risk breaking off the one stubborn Cylinder Head Screw p/n 308728 or should I separate the powerhead from Main Drive Shaft to attempt cleanout from underneath in those areas? I am unsure if powerhead has ever been separated on this engine (a mechanic replaced the water pump around 5 years ago. Unsure on this design if pump/impeller can be replaced without separating powerhead from Drive Shaft).
If I do attempt to remove the stuck cylinder head screw (other 7 of 8 screws have all been loosened) what is the best technique? Should I use Impact Driver with 1/2drive 3/8 socket vs. 3/8 socket with Breaker Bar? I have been soaking the stubborn screw with Liquid Wrench, transmission fluid etc for at least 1 week, but this screw is so tight I doubt that even capillary action is getting fluid in where it can do any good.
Thanks for any input.
So here is the question: should I risk breaking off the one stubborn Cylinder Head Screw p/n 308728 or should I separate the powerhead from Main Drive Shaft to attempt cleanout from underneath in those areas? I am unsure if powerhead has ever been separated on this engine (a mechanic replaced the water pump around 5 years ago. Unsure on this design if pump/impeller can be replaced without separating powerhead from Drive Shaft).
If I do attempt to remove the stuck cylinder head screw (other 7 of 8 screws have all been loosened) what is the best technique? Should I use Impact Driver with 1/2drive 3/8 socket vs. 3/8 socket with Breaker Bar? I have been soaking the stubborn screw with Liquid Wrench, transmission fluid etc for at least 1 week, but this screw is so tight I doubt that even capillary action is getting fluid in where it can do any good.
Thanks for any input.