You are Here: Technical Help > Marine Engines & Repowering Topics > Repowering Your Boat

Repair or Replace Marine Engines, Boat Engines, Used Marine Engines, Used Boat Engines

Performance Product Technologies Question & Answer Forum

Topic: Re-powering your Boat

Question:What options do I have if I'm looking to repair or replace my existing Marine Engine?

Response:It doesn't take long when looking at the price of new boats to start investigating the alternative option of replacing or repairing your existing marine engine. This forum covers the options of marine engine longblocks versus bobtail marine engines.

Engine Rotation - No matter whether you choose a longblock or complete bobtail engine the rotation will be a very important factor to evaluate. Rotation with marine engines is always viewed from behind the engine looking towards the flywheel. Standard rotation (left hand) means the flywheel is turning counter clockwise looking at it from the rear, or another way to think of it is that the harmonic balancer will turn clockwise when standing in front of the engine looking at it. Opposite rotation engines (right hand) were common years ago however not regularly produced today as the later variety of transmissions; Hurth & Velvet Drive have negated the need for this as the gears can rotate either direction without issue. 

Step #1 Understanding the Terminology

Marine Engine Longblock - This term generally refers to the cylinder block heads as well as the required internals of the engine. Generally marine engine longblocks do not include the intake manifold, engine circulating pump, or flywheel. Depending on the brand product the "tin ware" (oil pan, valve covers, timing chain cover) may or may not be included. Much like the flywheel, since the tin ware is not considered a "wear" item some manufacturers do not include this with their marine engine longblock products.

Bobtail Marine Engine -   This term generally refers to a complete new engine as required to complete a "drop-in" replacement project. Depending on the manufacturer of the product in question these products generally come complete with fuel, electrical, cooling, and exhaust systems as well as the engine mounts yielding it ready to drop right in when replacing a used up engine.

Complete Package -
This term refers to the combination of a bobtail engine and in the case of a sterndrive package the Transom Assembly/Shield (sometimes also refereed to as a gimbal assembly) along with the sterndrive. To read more about sterndrives versus inboards select this link. To read more about inboard drive variations select this link.

Mercruiser Packages - As of July 5, 2009, Mercruiser has stopped selling engine/sterndrive packages. To assemble your own package, you will need a bobtail, transom assembly and sterndrive. Follow the links to go to the appropriate product pages to build your package.

Volvo Penta - Volvo Penta still follows the traditional approach of grouping together complete packages.

Power Packages - This term refers to the growing market for partially completed engines. These range from new longblocks with the fuel and electrical system already installed to this level of content but also including the desired exhaust system. The real beauty with the power package is they work great for the customer that needs a replacement but most of their ancillary accessories are still in good shape and don't need to be replaced. The other application that the Power Packages work great for is when you have a 5.0L and want to go to a 5.7L, or you have a 260 Hp 5.7L and want the 300 Hp 5.7L, or when you have a carbureted motor but want EFI.

When it comes time to investigate the options there are several things to consider; first and foremost is the age and condition of the engine being replaced. If the engine itself is bad, but the exhaust  and other marine engine systems are in relatively good shape it can be a good option to simply replace the marine engine longblock. However, unless you intend to complete the work yourself one must always consider the labor associated with switching the attaching hardware over from the old marine engine to the new one. Common issues that arise when replacing a marine engine longblock are whether the intake manifold will match, making sure the flywheel is correct, making certain the ignition system matches properly, and making the necessary adjustments for mechanical versus electric fuel pumps. With marine engine longblocks there are either remanufactured or brand new options with the prices actually being very close to the same for either option.

If the determination is made that the complete marine engine needs to be replaced one may want to consider a complete bobtail marine engine. When replacing a complete bobtail marine engine you will need to determine if the existing coupler can be used and if the existing sterndrive or transmission will couple directly to this. In many cases of the engine is more than 10 years old you will likely have to change out the engine harness connection plug as these have changed over the years. It is also common to have exhaust changes since the exhaust systems have changed from 3 inch to 4 inch. There are several different manufacturer options as well as even the option of changing from one to the other if it makes more economical sense.

Longblocks

Marine Power

Crusader

Mercruiser

Marine Diesel