Hydraulic Lifter Preload

To understand hydraulic lifter preload a comparison must be made between the solid lifter and the hydraulic lifter. With a solid lifter a feeler gauge is used to set the lash between the valve tip and the rocker. This is because a gap is necessary to accommodate heat expansion in the valve train. With a hydraulic lifter the gap is set to zero lash and then a preload is set. This zero lash is why these lifters tend to have a quieter operation.Hydraulic Lifter

This is all accomplished with the use of a spring loaded plunger mechanism inside the lifter body. When we set the preload we are pushing the plunger into the lifter body. Excessive valve train noise will result from insufficient preload and low manifold vacuum or a rough idle from excessive preload.

With zero lash (gap) the pushrod should easily rotate in your fingers but should have no up and down movement. This procedure is easier to perform with the intake manifold removed because you can see the lifter and the heel of the cam lobe. Zero lash is set while the lifter is riding on the cam lobes heel or base-circle. The pushrod must be correctly seated into both the lifter and the rocker arm.

  1. To set the lifter preload turn the engine in its normal rotation until the exhaust lifter just starts to travel upwards.
  2. Adjust the intake valve to zero lash and then turn the rocker arm adjustment nut 1/2 to 1 turn, when unsure about something always use manufacturers specifications. This additional turning of the adjustment nut sets the lifter preload.
  3. Rotate the engine until the intake lifter travels all the way up and then almost all the way down.
  4. Now set the exhaust valve to zero lash and then turn the rocker arm adjustment nut 1/2 to 1 turn.

 

Return