i got a set of 66 closed chamber heads and i was looking for some rockers and some of the rockers said rail type. what does that mean?
The rocker is guided by the valve with 'rails' on the tip. If it is not guided by the rails, then it needs to be guided some other way. Clevelands, for example are fulcrum guided. Hipo 289s are pushrod guided. FEs are located on a shaft for guidance. Dave
The term, even though not proper, refers to the type of rocker arm used to keep the rocker arm tips in contact with the valve stem tips. There is another way to use non rail rockers by installing guide plates. However even doing this requires the old studs to be pulled, the pads machined down and the holes threaded for screw-in rocker studs. It's under these new studs that the guide plates are installed and held in position to keep the push rods in alignment thus keeping the rocker arms also from going out of alignment. Heads from 79 up to the last years of the 5L and 351 used a different mounting called pedistal mounts as well as different rocker arms that automaticlly kept the alignment. They all worked well in normal street application but once you start to modify for high rpm and heavy valve spring pressures and higher lifts then the stud method has the reliability advantage as well as the adjustability for performance cam use.
