To give an idea how much weight is in your typical engine, a crank shaft weighs approximately 50 pounds, a connecting rod and piston assembly are 4 to 6 pounds.  At any revolutions per minute (RPM) there is a substantial amount of weight reciprocating and rotating inside the engine block.  At 4000 RPM, 28 grams (1 ounce) of weight 4 degrees from center of the crankshaft produces 112 pounds of external force on the crankshaft.  This causes an overloading of main bearings, which increases bearing wear and significantly reduces the life of the engine.  It also takes away usable horsepower caused by the increased friction.

     The following chart shows how a specific weight is multiplied at different RPM's during engine operation.

     Whenever you rebuild an engine, insist on a quality balance job on your components.  As a standard, each component show weight within 1 gram of each other.  Your vibration dampner (except fluid or rattle dampner), flex-plate or flywheel, pressure plate and timing chain should be balanced with the crankshaft.   Due to the design of fluid dampners and "rattle" dampners, there are internal assemblies that throw the crankshaft out of balance.  They have to spin above 500 RPM to function as per their design.  Many people who do balancing recommend a good steel or stock dampner, because it will work well with most applications and can be balanced with the crankshaft.  The cost of this procedure will normally average between $200 to $350.

     This does add cost to the rebuild, but compared to the benefits, it can add to the engine, it is well worth every dollar spent.