Pushrod length is a critical measurement for any engine that uses them, especially when rocker arms with no adjustability are used. With the popularity of the OEM LS non-adjustable rocker arms, even in advanced engine builds, determining the correct pushrod length for your combination becomes all that much more critical.
To walk you through the process of determining the proper pushrod length Melling’s Tech Director, Cale Risinger, made the tech video. It’s not a difficult process, but it requires attention to detail and calipers capable of measuring down to the thousandth of an inch.
“You’ll need the lifters installed along with the cylinder head and head gasket installed and properly torqued,” Risinger starts. With the cylinder being checked sitting at top dead center, you can drop in the adjustable pushrod. Then you can install the rocker arms and torque them down.” One thing to note during this process is to make sure your adjustable pushrod is adjusted shorter than your expected length.
Once everything is torqued down, it’s time to open up the adjustable pushrod. “Unscrew the adjustable pushrod until all the slack is taken out of the rocker arm assembly,” directs Risinger. “This measurement is zero-lash. Remove the rocker arm assembly and the adjustable pushrod, without altering the adjustable pushrod’s length, and measure it.”
With hydraulic lifter valvetrains, most manufacturers and builders recommend a certain amount of lifter preload. With no adjustments available on the LS rocker arms being used in this example, that means the preload must be established via pushrod length. In this example, Melling recommends half of the lifter’s travel as the preload setting.
“In this example, we’re using an LS engine with a full lifter travel of 0.180-inch,” explains Risinger. “Adding half of that [.090-inch] to the measurement of our adjustable pushrod [7.373-inch], and that gives us gives us 7.462 inches.” Taking that measurement to Melling’s part seach, we find the closest pushrod length offered is 7.457 inches, which will reduce lifter preload by only .005 inch, and will work perfectly in this application.