"Major Overhaul: New cylinder
"Major Overhaul: New cylinder kits (pistons, piston rings, cylinder liners; if rods are good they are reused) new main, rod, camshaft, and balance shaft bearings; new oil pump; new/rebuilt blower and turbo; oil cooler pressure tested/replaced; crankshaft removed/checked/cleaned/polished; aftercooler pressure tested/replaced; new/rebuilt cylinder head; new injectors; cylinder block hot-tanked, cleaned and pressure tested; new/rebuilt fuel pump; new/rebuilt water pump; gear train inspected; exhaust manifold cleaned; camshaft inspected; governor inspected; blower drive inspected/replaced; governor drive inspected/replaced and all new gaskets and fuel/coolant hoses. Also, I'd recommend going to a new-style fuel rack (if you have the old style) The old style takes a screwdriver to adjust the rack; there are two screws you turn. With the new style, you loosen the lock nut, turn the screw, and lock it down with the nut. On the new style, each injector is independent of each other. If one injector sticks the engine will start smoking/knocking. On the old style rack, if one injector sticks wide open, ALL the injectors stick wide open. Then the engine runs away and blows up. It's just a little extra insurance to have a new-style rack installed.
Marvin is accurate with his $15-$20K/each overhaul estimate. The engines should be pulled to do a major overhaul.
You can, however, perform an in-frame overhaul if you have enough room to do so. I don't know how your engine room is configured, so I can't tell you if it would be easier/more cost efficient to go ahead and remove the engines. I can tell you though, if I were the mechanic I would want to remove the engines. (Although mechanics will have varying opinions) I can do a lot better job with the engine out in the open on a stand and the job would be MUCH easier on my end. But I don't know how much it would cost for the crane service to remove the engines......that could be a deciding factor for you. Plus when re-installing the engines, it makes for a good excuse to re-align the engine to the gearbox which might get rid of any vibrations you may have experienced before (If the engines were out of alignment)
If you detune the engines to 385HP, yes you will get a few more hours out of them....maybe up to 7-8K hours depending on how well you take care of the engines.
Now whether 770 total horsepower will be enough for your boat, I couldn't tell you. I know our 800HP towboats can easily push a couple of barges...and I imagine our towboats are MUCH heavier than your boat. But our 800 horse towboats are lucky if they make 6-7 knots even by themselves....
Hope this helped."
