Jana,
I had to replace a 2GM20F last year in a 1988 Hunter 30. I just bought this boat the year before. PO let the boat sit in the water for over five years without use. There was no compression in one of the cylinders. Surveyor did not find an issue when we bought the boat. Choice was to rebuild at $5800 or buy new at $6400 with new transmission, motor mounts, panel etc. No brainer there. Cost to remove and install was another $7K (Haulout, labor, etc). Fortuanately, no fiberglass work for removal and install. The engine came right out of the companionway without any problems. I did have to expand the engine compartment into the rear berth and modify the plywood that the stairs are mounted to since the new three cylinder engine is longer. Nothing a good afternoon in my woodshop could not fix.
One word of advice, have the fuel tank cleaned and inspected if you have not done so recently. I did not do that and this year was full of frustration with a new engine that was starving from fuel. Marina could not figure out why the engine was starving of fuel. They would test the boat in the slip.. no problem. I would motor out to point to sail and the engine would die. Sailed back to marina (thank goodness for the correct wind direction). Finally pulled the tank after a couple of months of the marina treating other possible causes to find 2 inches of crude on the bottom that was choking a screen in the fuel line inside the tank. Diagnosis - spashing of fuel in the tank loosened the junk on the bottom. We found the tank to leak after cleaning the inside. So I purchased a new tank.
Regarding the 3YM20... great engine, lot's of power to push a 11K pound boat. YM was recommended by service marina. Other suggested engines were less power. No problems with it so far and it is easier to service. Water pump screws face forward for easy access to impeller. Prior engine was a pain to access impeller. Also other frequent access points (ie dip sticks, fill points) are easy to get to as well.
Good luck on the project.
Tim
"Buying a new boat one part at at time"
