Lubrication Issues

• If a clicking or tapping noise steadily gets louder as you rev the engine, it's probably a "tappet" or upper valvetrain noise. This can be caused by excessive valve lash, low oil pressure or worn or damaged parts. Check the oil level first. Bring it up to full if it's low. Low oil pressure could be responsible if the noise persists. A low gauge reading can indicate serious internal engine problems that are keeping normal oil pressure from reaching the components of the upper valvetrain. Those problems include a clogged oil pump pickup screen or a dirty oil filter. Oil flow can also be hampered by using too thick of a viscosity fluid during cold weather. A related lubricated problem can be caused by worn, dirty or leaky lifters. If the low pressure restricts oil delivery to the lifters, they won't pump up or take the slack in the valvetrain. Excessive valve lash and noise can be caused by this collapsed lifter.
  
  Remove the valve cover if the problem is not caused by lubrication issues. Older import engines require period adjustments to the valve lashes, typically after 30,000 miles. Excessive space in the valvetrain is not only noisy, but accelerates wear of both parts. Slide a feeler gauge between the valve stem and rocker arm when the piston valve is fully closed. The adjustment procedure can be found in the car's manual if there is too much of a gap. It's important to note whether the adjustment is made to a hot or cold engine. If the engine uses a hydraulic lifter, the oil pressure pumps lifters when the engine is running to keep zero lash in the valvetrain. The rocker arms need adjusting if they are clattering. While the valve cover is open, inspect the components. The rocker arms, cam followers and/or valve stems might need replacing if they are too worn. Check for bent push rods and broken valve springs.
  
  

Raps and Knocks

• A deep rapping noise is usually a "rod knock," caused by extreme wear and damage on a bearing. This means a bearing is on track to fail, which will cause the engine to seize or to lock up and break a rod. Either case will cause major damage to the engine. Rod knocks are most commonly found in high mileage and improperly maintained engines. Other causes: low oil pressure, too light an oil viscosity, oil breakdown, excessive blowby from worn rings, dirty oil in the crankcase and abusive driving. You can check bearing wear by dropping the oil pan and inspecting the rod and main bearings.