MERCRUISER 5.0 TOP END ENGINE OVERHAUL


Due to medical and business issues, Cruis'n Rulz! sat unused for 3 years, from 2005-2008, although during this time she was run up to operating temp 3-4 times a year. I had done the exhaust manifolds in 1998, and was thinking about them in the back of my mind, realizing they should probably be looked after. Having towed the boat to the gas station in July 2007, with the hope at that time of getting out, she had sat for another year with that gas in the tank. 
So, with great effort, I managed to get her out for the July 4th Elliot bay fireworks show and the next 2 days boat camping. She was running poorly, sometimes dropping a hole under full throttle, and had poor throttle response. "Bad gas", I thought. 
After sitting on the hook overnight, the engine would not turn over. I thought the starting battery was low, but after several trys, it spun and started ok.
After the weekend was over, back home on the trailer, I ran through the normal flushing routine, running the engine up to temp on the muffs. It ran and sounded normal. I shut it down and returned 1/2 hour later and tried to restart it. No go. I realized now it was not the battery; the engine was hydro-locking. The starter suddenly started growling and was clearly damaged from the effort. I pulled the plugs, and sure enough clear water spurted from several cylinders when cranked.
I squirted ATF into the plug holes and performed a compression test. 150 all around. Maybe I got lucky....Several minutes later, I went to crank it again. The starter sounded like a garbage truck, and the engine spun 3 revolutions and seized. Putting a chain wrench on the balancer, I found I could not advance the crankshaft, but could turn it backwards. Rotating forwards, it stopped at the same point. The only reasonable thing it could be was a stuck valve, so I pulled the valve covers. The #4 cylinder exhaust valve spring was compressed, and the rocker loose. The situation was deteriorating rapidly.
I pulled the manifold on the right bank. Feeling into the #4 exhaust port with my finger, I could feel the broken off valve stem. This then was the source of the seizure, The #4 exhaust valve head was loose in the cylinder, jamming the piston. The port was very rusty looking, and I knew at this point I was in for a whole lotta work.
Follow the links below. They will take you through, dissassembly, cleaning, painting, and reassembling.
Dissassembly and inspection
Cleaning and prepping block and pistons
New Parts Preparation
Parts ready for installation
Assembly and finishing

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