The Terminology used when referring to a marine engine can be confusing. Longblock, shortblock, bobtail, partial, what do you call the thing?
Use the tabs above for some explanations. We will start with the complete engine first.
Complete engine, also called a "drop in" is the complete engine including all external components ready to install in the boat. From an installation standpoint this is by far the easiest. Unfortunately it is also the most expensive. However there are some real benefits, the biggest being a full warranty on the whole thing.
A bobtail engine is generally complete and ready to install.
A crate engine is an assembled longblock with some external components. In the case of Mercruiser crate engines the water circulating pump, intake, fuel (including pump and ECM if fuel injected) & ignition system are included. This is a much better bet than a longblock but the other accessories need to be installed. This is also called a partial.
In general a longblock is an assembled block with pistons, crank, pistons, cam, etc and assembled cylinder heads. The "tin" which includes oil pan, valve covers and timing cover is also included.
Installation is more complicated as all the other components need to be transferred from the old engine. There are many things that can go wrong and the warranty is for the longblock only. If you blow a hose or overheat it with a bad water pump there is no warranty. We do not recommend longblocks unless there is no other choice.
CPO is a Mercury designation for a product or engine that is Certified Pre Owned.
A CPO has been remanufactured to originaial specifications and come with a one year warranty.
However CPO products will show some evidence of use: scratches, cosmetic corrosion, and any number of hours are possible. Corrosion on the flywheel, alternator, exhaust ports, water jackets, midsections, and lower units are also possible.
In general the CPO products are a great value!