Noisy Hydraulic lifters can be caused by several reasons, none of which are due to a defective lifter and as a result, are NOT covered by warranty.

1.  The most common cause is particles in the oil getting jammed between the lifter plunger and the lifter body, causing the plunger to become “stuck down”

The clearances between the plunger and body of a Hydraulic lifter can be as little as .00012”,  .003mm.  or 3 Microns (1/30th of a Human Hair)  Any particle larger than this circulating in the oil has the potential to flow through the lifter and jam the plunger in the body.  This is especially common after a rebuild where particles are left in oil galleries or crevices, and find their way into lifters.   Replacement of the lifters usually fixes the problem, as all the initial dirt has been captured by the lifters or the filter.

Note some “Racing” oil filters only filter down to 27 Microns and may not be suitable for Hydraulic lifter engines.

2. Aeration of oil in the pressure chamber of the lifter can cause noise.  This may be the result of air in the high pressure chamber of the lifter affecting valve train lash. When this occurs, valve closing velocity is increased, which causes the noise. Air can be present in the lifter at shutdown due to an aerated oil condition, or it can be ingested into the lifter during a cold start from a suction side leak at the oil pump or oil pump pick up tube o-ring. Oil aeration level, oil viscosity, time to achieve oil pressure, engine speed, and lifter design all play a part in whether lifter noise is observed. Once air gets into the high pressure chamber, it will slowly be expelled through the very tight clearance of the plunger and body.  Aeration can be caused at high RPM by low oil levels or an incorrectly designed oiling system.  This will result in lifters becoming “spongy” and will significantly affect the valve train operation.

3. If the engine has been off for a few hours or more, the valve spring may cause the lifter to leak down where the valve is open.  This is normal and the noise should stop after a few seconds, and at the most after several minutes.

4. “Lifter” noise has also found to be caused by loose Piston Wrist Pins, Piston slap or Roller Rocker arm noise!