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During the balancing process, bob weights are bolted to the crankshaft. They’re equal in mass to 100 percent of the rotating weight (big rod ends, rod bearings), and 50 percent of the reciprocating weight (pistons, pins, locks, small rod ends). With today’s lightweight rods and pistons, material is typically removed from the crank counterweights, although heavy metal is sometimes added in extremely long-stroke cranks that have small counterweights. Since a crankshaft acts as a lever, the farther away from the crank centerline the weight is removed, the greater affect it has on balance.