115 hp yamaha compression low help

[pursuit001]

hi all i have a 1995 model 115hp yamaha which was running fine then stopped like it was starving for fuel and will no longer start now i have tested the compressions 140psi on 3 cylinders and on number 4 it is o psi i removed the bottom 2 plugs and both are showing signs of water rust marks on the plugs would this be a blown head gasket or has it dropped a ring it has spark and plenty of compression on all the others cylinders but will not fire im thinking when its on the muffs that when firing it if its a head gasket blown that its filling the pots with water on the bottom two cylinders and not allowing it to fire so what do yous think where to start blown head gasket or dropped a ring ???????

[STUIE63]

either way you will have too take the head off so that is where I would start . my guess is gasket though

[pursuit001]

thats what i was thinking makes sense to me that when you put the the muffs on it filling the 2 bottom cylinders as its a loop charge eninge so as it fires its filling the pots with water still yet to try it without water connected to see whether it fires you would think if it was a ring it would atleast have some compression being a loop charge engine as it fires it will be firing filling one pot then throwing water back through the exuast into pot number 4 as its only the bottom 2 cylinders that the plugs are showing signs of water rust marks on plugs

[djfish71]

I doubt it would be the head gasket as they are separate gaskets for port & starboard cylinders, sounds more like the lower crankshaft seal has leaked, they should be changed about every 5 years on those engines, just to be on the safe side.