| Just a word on roller rocker arm tips: they are sold to guys under the premise that they reduce friction. They are really there to make up for suboptimal geometry and inferior guide materials. As the rocker pivot moves to either side of its optimal position, the amount of relative motion between the wiper-style valve tip contact feature (called the pallet) and the valve tip increases greatly. This relative motion, (called scrub) applies a side load on the valve stem. This can cause wear on the cold end of bronze valve guides. A roller on the tip of the rocker reduces that valve stem side loading and it helps guides live longer. It also makes up for everyone who has a fresh valve job cut that moves the valve up 0.050″, and now their rocker pivot is too low. Since BBC head rocker stud bolt holes aren’t parallel to the valve, shimming the stand moves the pivot up that 0.050″ vertically, but it also moves the arm toward the valve, making the pattern uncentered on the valve tip. Engine builders tend to look for a centered pattern, while valvetrain engineers want the pivot at the right height before having a centered pattern, if they can’t have both. The roller is more forgiving for the guy who sets his stand height by valve tip pattern. The truth is if you had your own valvetrain engineer designing your system, he’d likely use a fixed pallet (wiper) over a roller tip. |
