The key parts of any camshaft are the lobes. As the camshaft spins, the lobes open and close the intake and exhaust valves in time with the motion of the piston. It turns out there is a direct relationship between the shape of the cam lobes and the way the engine performs in different speed ranges. It is highly recommended that you change the rocker arms with every cam change and keep them together as a package or kit. The reason is, rocker arms burnish themselves to each cam lobe. As we know, each cam is ground on a different angle and each rocker arm wears at a different angle. If you use rocker arms from one camshaft to another, they will most likely trough into the new cam lobes.
The four most common causes of premature camshaft failure:
- Improper break in procedure. Excessive or long cranking on initial start up. Engine must start immediately and run at 1600-1800 rpm's for 20-30 minutes.
- Improper rocker geometry, changed by: increased camshaft lobe lift, valve tip height and rocker stand height.
- mproper valve springs. Inadequate clearance between coils (coil bind), spring pressure too high or spring pressure too light.
- Reground camshafts with reduced base circle diameters will cause premature lobe and rocker wear.
Rocker Arm Burnish
- To correct rocker arm contact pattern, mark the rocker arm with a black ink marker, rotate engine two (2) complete revolutions, inspect contact pattern. If ink is wiped off nose or heel of rocker arm, you will need to adjust the rocker shaft stands.
- Usually milling the stands .015" / .020" will center the pattern.
- Always check valve to piston clearance. The minimum clearance should be .100", if using an adjustable cam gear, check with full advance and retard to assure adequate clearance.