Sportjet 175 flywheel only turns approx 270 degree by hand

[pumper]

We just picked up a 2000 Cutter 17ft with merc sportjet 175 jet drive. owner says the engine stopped on him this past summer after running it at low rpms through a river followed by WOT. Flywheel turns smoothly with socket and bar not quite full rotation ( 280 degrees) either way and does not feel like anything dragging..just stops. Before pulling the engine, does anyone have any ideas of the cause or troubleshoot cause other than major interior engine failure. i.e pump/ gear /impeller issue. Thanks

 

[Cobra Jet Steering LLC]

remove the plugs and look inside also look at the plugs if one is smashed you know the engine threw a rod

 

[pumper]

That makes sense. Thanks for the tip. Will follow up with my observations

 

[pumper]

Pulled the engine out , removed head and crank covers off today and found #2 port piston melted so bad that it had debris jamming at the ports and tons of aluminum debris on walls of bore. Crank looks fines at initial inspection . Rest of the pistons also look fine at this stage of tear down but plastic oil pump gear surface is damaged and seems loose. Would an oil pump failure be the only cause of only one piston to be destroyed like that. It also had iridium style plugs installed by previous owner which all looked normal.

 

[pumper]

Before I rebuild with new #4 piston ( not #2 port as mentioned last post) and new rings on rest, I am still trying to figure out what caused #4 piston to melt. Here is a pic of the heads (top head- center is the one that had melted piston) and the piston Can anyone tell from the coloration or damage pattern what may have been the cause? Leak at head?, too lean mix from carb, etc?? I don't want a repeat. Any help appreciated