A complement of modified and balanced connecting rods, wrist pins, and pistons ready to be installed.  These were all lightened as a set.

Like automobile engines, consumer outboard engines are carefully designed and built to perform well reliably. But most of the time, their design is an exercise in compromise. The engines must be produced in a manner that is cost effective while providing reliable performance for their class. As we all know, this leaves much room for improvement on a factory stock engine.

While there are many aftermarket and factory upgrade parts that can be added to provide increased performance on most outboard engines, there is another side of this modification process that is often underestimated in value and overlooked – lightening and balancing the rotating assembly. This process is also known as blueprinting.

An engine’s rotating assembly is defined as all of the components connected to and including the engine’s crankshaft. This includes the flywheel, pistons, connecting rods, and wrist pins. In a 4-stroke engine, the rotating assembly would also include camshafts, sprockets, and cam chains or belts.

For an internal combustion engine to produce power output, there are two types of energy being produced as the combustion process is carried out.  These types of energy can be broken down to either rotating energy or reciprocating energy.

Rotating Energy: the crankshaft, cams (in a 4-stroke engine), and the flywheel displace energy produced by the combustion process for the engine to produce power. The result is rotating energy that can be used to turn the propeller.

Reciprocating Energy: pistons, connecting rods, and wrist pins move in a back-and-forth motion as part of the process required to produce combustion. These components are driven by combustion, which is converted into rotating energy for the crankshaft.

Fully lightened, pinned, and balanced assembly is better suited to withstand the punishment of constant high RPM use.

In both situations, the rotating assembly components work together to produce the engine’s horsepower output. Those components must be able to withstand high operating stresses and temperatures while being machined to very close tolerances. Pistons, connecting rods, and wrist pins are designed to be matching components in an engine; however, the actual weights of these components can indeed vary. This is where blueprinting becomes important. If performed correctly, lightening and balancing the pistons, connecting rods, wrist pins, and the flywheel will not only allow the engine to develop more horsepower faster, but it will increase engine reliability as well by reducing bearing loads. Since the crankshaft and its connected components operate as a unit, the more precisely those components are balanced, the less off-axis loads are created, resulting in less wasted energy.  For every gram out of balance a connecting rod is, the working component weight squares per thousand RPM.