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Hydro locked 7.4 Mercruiser

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Snakeriversailor77

Contributing Member
I'm working on a Mercruiser 7.4. The engine was run and stopped suddenly. Checking it and pulling the plugs water was found in all the cylinders. This is a closed system engine and the reservoir tank was still full. No water was found in the oil. A compression check showed it to be good except #1 which had none. Pulling the heads didn't show any obvious damage . The heads and exhaust manifolds showed inordinate amount of rust. The engine showed that it had been taken apart previously and I'm thinking the flappers failed and caused the previous problem and this one too.hoping for the best and having the heads freshened and manifolds checked. Push rods may need replacement too. Has anyone else dealt with something similar. Hoping the rods aren't bent. Anything else I should look at?
 
Pull the heads, most times the valve tulip or pucker from the blast of cold water.pull all the valves and inspect the head and valve seat areas for cracks.
 
The engine must come apart completely and have all components checked. In your case a reconditioned long block is probably a better way to go. You'll get back on the water faster and it will likely be less money.
 
The customer was advised to go with a long block but didn't want to. Ordered new manifolds and risers. The old ones had corroded and failed at the riser manifold gasket face. Didn't find antifreeze in the manifolds and the closed system was still full when I disassembled it. The new manifolds wanted me to specify antifreeze or no antifreeze in manifolds and I indicated they didn't. Still wondering if I was correct. Anyone know for sure, 7.4 L MPI, hose from cooling comes in on the bottom.
 
.A compression check showed it to be good except #1 which had none. Pulling the heads didn't show any obvious damage .

engine serial number would be helpfull some pics of what you have there, a full system would include the manifolds with A/F . damaged valves in#1
 
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