Correct pushrod length is dictated by rocker arm geometry. This means the rocker arm tip must operate at the center of the valve tip, across its widest diameter. If it operates off center—say, closer to the intake manifold—the pushrod is too short. Closer to the exhaust manifold indicates it’s too long.
How do you know if your pushrods are too long?
A sure indication that the pushrod is too long is when it takes more than 1 full turn to seat the rocker past the zero-lash point. Though we have successfully run pushrods with more than 1.5 turns, more than 2 turns can actually hold the valve open once the lifter is pumped up with sufficient oil pressure.
How do you determine pushrod length with hydraulic lifters?
The roller tip on the rocker should have left a shiny spot where it wore away the ink you placed on the valve tip. If the pushrod length is correct, this mark should be centered across the top of the valve stem. If it is too high (closer to the lifter valley), try a slightly longer pushrod or lengthen the checker.
What is rocker ratio?
Rocker 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.
How important is pushrod length?
An ideal pushrod length will minimize the distance that the valve trip travels across the valve tip. Pushrods that are either too long or too short only increase this distance. A too-short pushrod positions the rocker tip too far to the intake (inboard) side of the valve tip.
Do you add lifter preload to pushrod length?
Each revolution is worth 0.050-inch so if the count is 10 turns (from the base length of 6.80-inches), that adds 0.500-inch to the original length of the pushrod. In this case, this puts the pushrod length at 7.300-inch. Now all we have to do is add the desired amount of lifter preload to that 7.300-inch length.
