How the cam opens the valves

A separate motion study for the inline-six: the cam raises a lifter, the pushrod rocks a lever, and the opposite end opens the valve. Each cylinder repeats once every two crankshaft turns.

Teaching candidate, not the installed engine model. Timing landmarks come from the applicable Melling SYB-38 replacement catalog. The smooth cam curve, base circle and linkage dimensions are assumptions. The truck's actual cam identity is unknown.

Cylinder Crank angle 0°

● Intake● Exhaust

What is measured, and what remains assumed?

The manufacturer lists .247-inch cam lift, .395-inch valve lift, 192° duration at .050-inch lifter lift, 270° advertised duration, a nominal1.6 rocker ratio and intake/exhaust centerlines108°/114°. Rounded catalog valve lift does not exactly equal .247×1.6.

The advertised duration's checking height is not supplied. This study assumes zero lift at the ends of a270° window and interpolates a smooth curve through the catalog lift landmarks. It does not reproduce a measured Ford lobe or model spring dynamics, lash, piston contact, tappet crown or hydraulic internals.

The diagram solves a fixed-length pushrod and sliding valve pad. Its joint centers are coplanar at rest. The installed CAD's cup/pad heights and head pedestal must be revised and swept for clearance before this can drive the assembled model.

Melling camshaft catalog, page13 · Candidate checks