Thread: Push Rod length

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Sean, I think what Pat was sayin' is that the checker you're using might work differently rocker to rocker, as he has gotten different results using using it and prefers not to use it any longer. Apparently he uses the same method most of us use and that is to verify that the rocker tip travels through its arc making the shortest possible trip across the valve tip and the extremes to the intake side and the exhaust side are equal.

The rocker changes its effective ratio as it swings through its arc. The ideal setup would be: Starting off at zero lift with the rocker tip on the intake manifold side of the valve, then moving to the exhaust manifold side of the valve at mid-lift, then coming back to the intake side of the valve at full lift. On the return trip to zero lift, the roller would cross the center of the valve tip and go to the exhaust side of the motor at mid-lift, then back to the intake side of the motor with the valve back on its seat. In this way, the rocker would be at its longest effective length halfway through the lifting of the valve. Its effective length would be shorter at both zero and full lift.

Whether you're using an adjustable checking pushrod or a pushrod that you think might work correctly, de-grease the valve stem tip and color it with a black Sharpie pen. Then, install the pushrod and rocker arm while the lifter is on the base circle of the cam. With hydraulic lifters, jiggle the pushrod up and down while tightening the adjusting nut until all play is removed. Twisting the pushrod with your finger and thumb will not work. You'll be compressing the spring and not even know it. Jiggle the pushrod up and down to remove play. With all play removed, tighten down the rocker adjusting nut to your normal preload. Using a socket on the damper retainer bolt head at the front of the crankshaft and long bar for leverage, turn the motor over several times clockwise. Obviously this is more easily done if the spark plugs are out of the heads. Remove the rocker and check the mark left on the valve tip. The roller tip on the rocker should leave a shiny spot in the center of the valve tip where it wore away the ink you put on the valve tip. The width of the shiny area will tell you the intake side to exhaust side extremes of travel of the rocker tip across the valve tip. Measure this width with your dial caliper and record it in your toolbox notebook.

If the pushrod length is correct, this mark should be centered across the valve stem. If it's too high (closer to the intake manifold), try a slightly longer pushrod. If it's too low (closer to the exhaust manifold), try a slightly shorter pushrod. This method works well when using an adjustable checking pushrod.