the extension 28 includes portions 40 that extend laterally of the vertical axis of the cap 26 the portions having symmetrically arranged apertures or pivot pin holes 42 44 is a lightening hole the central fulcrum portion 32 of each mass consists essentially of a journal bearing 46 with flanged sleeve like insert guides 48 that receive a pivot pin 50 therethrough each pin has a hole 52 through which the main bearing cap bolt 24 passes the clamping force of the bolt elastically deforms the round hole 40 against the pin 50 preventing motion of the pin washers and lock rings are also indicated to maintain the masses in position completing the construction each leg portion 34 36 of the mass has mounted thereon a low friction cam follower in fig1 4 it consists of a sliding shoe 54 that is pivotally connected at 56 to the mass the shoes have concave outer surfaces 58 fig4 that are adapted to be engaged by the contoured cam surface 60 of a cam 62 formed as an addition to the usual crankshaft cheek the cam in this case has a somewhat elliptical shape with major and minor axes providing small and large radii the concave surface 58 of the sliding shoe followers are shaped to fit the longest cam radius and provide a rocking freedom of movement to compensate for the varying angle between the cam face and the balancer arm the opposite side of the shoe is mated to a cylindrical or spherical surface on.