Engine Balancing and Blueprinting, although they are sometimes thought of as one and the same, balancing and blueprinting are separate and different procedures. Balancing refers to removing weight from the flywheels, or adding it, to equalize weight distribution.
Blueprinting refers to any of a number of procedures used by engine builders to make sure that the dimensions of various engine parts, and their operating clearances, fall within a certain range.
Balancing and blueprinting are often mentioned together because one naturally follows the other as the engine builder prepares components for final assembly. Balancing is the more complicated of the two, so we'll start there. By first discus the anatomy of a engine, and take it from their. Then we'll discuss why first-rate balancing and blueprinting are so important. The engine anatomy, the V-twin crankshaft assemblies consist of two flywheels, two connecting rods, a crankpin that joins the flywheels near their outer edges and anchors the connecting rods, two shafts that support the crankshaft assembly in the crankcase, and a handful of smaller parts, including bearings and cages, crankpin nuts, crankpin nut lockplates, and lockplate retaining screws. For a single cylinder engine the design is much the same, understandable has a single cylinder engine for some parts one and not two, the main difference between a single and two-cylinder engine.
For balancing purposes, the pistons and their related parts, rings, wrist pins and wrist pin keepers, can also be considered part of the assembly.
A glance at a V-twin crankshaft reveals why it requires careful balancing. The crankpin, connecting rods, pistons, and other components weight thousands of grams. Instead of being distributed evenly around the flywheels, that weight is concentrated at the crankpin. To greatly reduce the vibration this would cause, manufacturers create a counterweight by making the flywheels heavier and the side opposite the crankpin.
To equalize weight distribution, the weight on the crankpin and the flywheels counterweight, the mechanic balancing the lower end removes weight from the counterweight by drilling holes in them. Extremely light or irregularly shaped flywheels and heavy. Big-bore pistons require that weight be added to the counterweight. This is usually accomplished by drilling holes and filling them with Mallory metal, a heavy tungsten alloy that has more mass than the steel removed by drilling.
Before making any changes to the flywheels, the engine builder needs to attach a bobweight. The formula used to determine the weight of the bobweight is: (reciprocating weight x balance factor) + (rotating weight)/2.
As the formula indicates, component weight, which is what the bobweight is mimicking, is divided into two categories: Rotating weight and reciprocating weight. Rotating weight does exactly that - it rotates. The crankpin, crankpin nuts, lockplates, and screws (if have), connecting rod bearing assemblies, and connecting rods are attached to the flywheels and rotate with them. They comprise the rotating weight. Reciprocating weight moves up and down with the pistons. Reciprocating parts include the pistons, pistons rings, wrist pins, wrist pin retainers, and connecting rods. Did you notice that the connecting rods are listed as both rotating and reciprocating weight? Because the bottom of the rods is anchored to the flywheels, it rotates with them and is included in the rotating weight. The upper portions of the connecting rods, however, are attached to the pistons and travel back and forth with them, so they are included in the reciprocating weight.
The rotating weight of each rod is determined by placing the crankpin end on a gram scale and suspending the other end from a thin piece of string or placing it on a balance stand. I prefer to use a fishing line, and remember not try to hold it in your hand, even the most steady hand shacks. After carefully leveling the rod, the mechanic notes the weight indicated on the scale. The procedure is reversed to determine reciprocating weight: The rotating end is suspended and the reciprocating end weighed. If don correctly, the rotating and reciprocating weight will equal the total weight of the rod.
Now, let's talk about balance factors, which represent a percentage of the reciprocating weight. Traditionally, engine builders have used a balance factor of 58 to 60 percent for street engines, and factors as low as 52 percent for high-revving race engines.