FAQ Index Rod & Main Bearing Clearance Alum Rods Octane Test Rocker Arm Geometry 1972 Cylinder Head End Bolt Hole Clamp POLY-LOCK ADJUSTMENT   INSTALLED HEIGHT DIMENSION   LIFTER BORE BRACE

Valvetrain Geometry Rocker arm geometry is important to the stability and durability of a racing valve train. TD rocker systems include instructions, an index tool, and a mock-up push rod to make it easy to get the right geometry when using their ahft system. The vertical location of the rocker shaft is a significant factor in valve train geometry. The correct shaft centerline position will locate the roller tip at the same position on the valve stem tip when the valve is closed and when it is at full lift. At the valve closed position, the roller should be slightly behind the valve stem centerline. The roller tip should sweep across the tip to slightly ahead the the stem centerline as the valve opens to mid-lift position, sweeping back to its starting point behind the centerline at full lift Rocker Ratio Rocker arm ratio is determined by the relationship between the push rod cup, the rocker shaft centerline, and the roller tip. TD machines these critical dimensions to close tolerances to ensure accurate rocker arm ratios. Discrepancies in rocker arm ratio will occur because the motion of the roller tip describes an arc, The valve stem axis is tangent to this arc. Because of this relationship some of the roller tip motion is directed across the valve stem instead of in a direct line along the stem axis. This can account for discrepancies in valve lift based on mechanical rocker arm ratios.