Own and operate any boat long enough and you'll face this costly choice. Your engine will need major repairs, or it will need to be rebuilt or replaced altogether. If you choose to replace your old engine with a new one, know this: There's a lot more to repowering a boat with a stern drive or an inboard than just swapping engines.
Before you start, find out if the job is worth the money. Rarely does the market value of a boat increase enough to justify the cost of repowering. It's often smarter to simply repair your old engine or install a rebuilt engine instead of a new one, then sell or trade in your boat, moving up to a new model.
How much will your old boat be worth with new power? To find out, log on to www.nada.org for an estimate. Also, if you own an older, larger model, hire a marine surveyor to evaluate your boat's worth. It may suffer from other problems that would make repowering pointless. Of course, if you plan to own the boat for another dozen years or so, the cost of repowering may be significantly less than buying a new boat.
Your next task is to find out why the engine failed. Marinized engines rarely wear out, especially during the first 10 years of operation. Usually it's problems with components or poor maintenance that cause engine failure, not wear and tear. Unless the cause of the failure is determined, you may be wasting your money-especially if you're buying the block and intend to use the same alternator, starter, pumps, wiring harness, and so on. Each component should be tested before reuse. If your boat is an I/O, you may want to consider a new outdrive or, at the very least, having your existing outdrive rebuilt. There could also be problems associated with the airflow in the engine compartment. Or you may need to check out the drive train, including running gear and alignment.