I replaced a 1980's era Ford diesel
with a new John Deere 4045 and a ZF63. On the way I replaced or upgraded all filters and fuel lines, installed an electric
to facilitate bleeding, put in new control pod and a 4" exhaust
with a new waterlift muffler
The Ford was totally on it's last legs. Would only start with liberal doses of "Aerostart". When it was partially dismantled it was found to have bent pushrods.
I now have the pleasure of an engine that starts in less time than I can measure, easily pushes the boat
to its hull speed
, and improves maneuvering. Engine and gearbox
are rated to run 24/7 at full power, with a gearbox
that is greatly overrated.
For the cost and the pleasure, not to mention the reliability
I'd suggest going with a new engine and gearbox. It should be assembled by trained workers to specification using the right tools in a clean environment
. My experience with rebuilt engines has not been happy.
On the way you have the luxury of matching the engine with the boat, specifying a heavy duty gearbox and upgrading controls, fuel system and exhaust
Starting the engine at any time to motor
through a period of enhanced risk should not depend on it's reliability
Expensive - but probably not compared with engine troubles at a bad time.