Roller Rockers are a common upgrade for any performance engine build. They reduce friction which in turn frees up more power. There are 2 common types of roller rockers found on small block Fords pedestal mount rockers and stud mount rockers. Each rocker set up gets its name by the way they mount to the heads.
Pedestal mount rockers basically sit on a flat mounting boss that is built into the head itself. The “pedestal” part of the rocker arm sits on top of the boss and has a machined cradle in it that allows the rocker arm to sit down inside it. This cradle is what supports the rocker trunion and allows it to move. These rockers are held in place by a single bolt that goes down through the entire rocker assembly and threads into the mounting boss that is built into the head. The pedestal rockers normally don’t need any adjustment, however in some extreme cases they do. To adjust them, shims are placed in between the mounting boss and the “cradle” that the rocker sits in. The adding or removing of shims shifts the rocker assembly up or down which in turn changes the contact pattern on the valve.
The second common rocker configuration is the stud mount. These are going to be easily identified by wither a 3/8” or 7/16” stud coming up through the rocker arm assembly. The stud mounts don’t have a set base that they sit on. This requires them to be adjusted or “set” to achieve a proper contact pattern on the valve. The stud mount rockers are held in place by a locking retainer nut. Once the desired valve lash is achieved, the locking nut is set in place by the threaded allen head “lock” that is in the middle of main rocker arm nut. This keeps the rocker arm nut from moving and changing your valve lash adjustment.
Adjusting your rocker arms correctly is crucial to the overall performance and life of your motor. Improperly adjusted valves will cause pre-mature wear on your valvetrain that can lead to catastrophic failure.
When installing pedestal mount rockers, make sure you properly lube the rockers, attaching hardware and also make sure the flat side of the rocker trunion is facing up. First step is to make sure the cylinder you are working on has the cam lobes positioned so that both valves are in the closed position. Next, make sure the push rods are seated in the cups and tighten up the mounting bolts by hand until they are snug. When they are snug, you should still be able to spin the pushrod, but not have any up and down end play. Torque the mounting bolt to 15 ft/lb (or recommended manufacturer torque spec for aftermarket rockers). After the rockers are torqued, you should still be able to spin the pushrod. If you are not able to spin the pushrod, shims are needed for additional clearance. If your pushrods are too short and have excessive end play, you need to measure for longer pushrods.
Installing stud mount rockers is similar to pedestal mount installation. Make sure the flat side of the rocker trunion is facing up and slide the rocker assembly down over the stud. Lube the stud and install the retaining nut onto the threads making sure the allen head lock screw is backed out. With the cylinder you are working on at top dead center (TDC) or where the camshaft would have both valve in the closed position, tighten the retaining nut by hand until there is zero lash. You should be able to spin the pushrod freely with no up and down endplay movement. Once you have achieved zero lash, turn the retaining nut an additional quarter to half a turn to set the pre-load on the lifter. As soon as you set pre-load, screw down the allen headed lock to set it in place and prevent the retaining nut from moving.
Now that the 2 most common styles of rockers have been established, lets move on to rocker arm ratio. Rocker Arm Ratio is the length of the valve side of the rocker arm to the center (or pivot point) of the rocker arm divided by the length of the Cam or Pushrod side to the center of the rocker arm. Typically the valve side is longer than the pushrod or cam side, so the rocker arm will "multiply" its motion by its Rocker Ratio. This ratio is typically in the range of 1.6 to 1.7, meaning that for each .100" of pushrod or cam motion you would get .160" to .170" of valve motion. Changing the rocker arm ratio on your engine will have a direct effect on your camshaft lift specifications. The higher the ratio rocker you use, the more valve lift you will see. For instance the Ford Racing “E” cam part number M-6250-E303 is based off of a 1.6 roller rocker and has a lift of .498”. If you change your rockers to a 1.7 roller rocker arm, it will change that lift to .529” just by swapping rocker arms. This is an easy way to modify your cam specs, but must be used with caution. You can’t just blindly throw larger ratio rockers on your current set up to achieve more lift. You have to make sure that the rest of your set up (springs, retainers, valve-train geometry etc.) will function properly with this change.