1980/90 mercruiser 3.0 140 hp /water in oil/ explosion sound💥

[samerama50]

Hi everybody, i bought a projet boat with a mercruier 3.0 L 140hp who didn't run for few years ,what i did :
-Emptied oil and was full of water but not milky, oil and water were separated from each other
- put new oil
- rebuilt the Mecanical gas pump and changed all filters
- compression test cylindre 1 and 4 had compression around 125 psi
BUT 2 and 3 nod nothing 0 zero !!!
- put new spark pulgs
- i thought just to give it a try and see what happens, it took a while to start but as soon as it start it do like explosion sound so i shut off , Each time i start it its give same sound of explosion abd i never passed a 1 second running the engine
So what shout i do from here and what do you think about : the water in oil
No compression cyl 2 and 3
Explosion when running
Thanks in advance .

 

[Scott06]

Valves are staying open in cylinders 2&3 explosion is backfire or exhaust valve is open when the cylinder fires. Likely the water in the engine means the parts of the engine are rusted like valves

Tear the engine down or at least take the head off and see what you have but if you had water in the crank case for a long period of time the engine will need to be rebuilt

 

[samerama50]

Valves are staying open in cylinders 2&3 explosion is backfire or exhaust valve is open when the cylinder fires. Likely the water in the engine means the parts of the engine are rusted like valves

Tear the engine down or at least take the head off and see what you have but if you had water in the crank case for a long period of time the engine will need to be rebuilt

Thx i will try to open the head this weekend and see as you said

 

[samerama50]

I opened the valve cover all seems to be good but one spring is lower than all other , i tapped on it but didn't move up , what should i do next ? Thx

 

[Scott06]

I opened the valve cover all seems to be good but one spring is lower than all other , i tapped on it but didn't move up , what should i do next ? Thx

This valve is stuck open as said remove the head. Take head to machine shop for valve job may need new guides and valves won’t know until you strip it down

 

[itsathepete]

At the very least you have a bent and stuck valve. You likely had a piston hit that valve and damage the piston. Pull the head and look.