Cam Walk (Axial Thrust) Phenomenon The tell-tale signs are a worn thrust face on the block (if movement was backward) or a scored timing chain cover (if movement was forward), or excessive wear of the cam’s distributor drive gear.

Generally, the recommended amount of end play is between 0.003 in. and 0.010 in. Always follow the camshaft manufacturer’s instructions when measuring and adjusting.

The flat-tappet cam lobe is more pointed at peak lift, while the roller cam nose tends to be rounded; this means the roller is holding the valve open at higher lift for a longer period of time, which results in a greater fuel/air charge. The lobe shape also opens the valve much faster.

The big advantage roller cams have over their flat-tappet cousins isn’t the reduced friction most people immediately think of, it’s increased tappet velocity (i.e., faster ramp rates). This increased velocity, as much as 30 percent, equates to more power.

Flat-tappet cam lobes are ground at a very slight angle to prevent the cam from moving. Roller cams cannot be machined this way, so a roller-cam button is employed to limit cam movement.

There are four types of lifter designs and matching camshafts currently available for the big-block Chevy: flat-tappet in either mechanical (fixed length) and hydraulic (self-adjusting), and roller lifters that have a roller bearing that follows the contours of the cam lobe, also in either mechanical or hydraulic.

They can run anywhere from $450 to over $550 a set depending on the specifics. So compared to a typical $65 – $75 set fo flat tappet lifters, a set of roller lifters is going to set you back a bit more $, but in the end, for what you gain in performance & reliability, it is well worth it.