F 350 4WD Pickup V8-351 5.8L VIN H EFI (1997)
A sticking tappet plunger can be caused by dirt, chips or varnish inside the tappet. This condition can be corrected by disassembling the valve tappet and
removing the dirt, chips or varnish that are causing the condition.
A nonfunctioning tappet check valve can be caused by an obstruction (such as dirt or chips) preventing it from closing when the cam lobe is lifting the
valve tappet. It can also be caused by a broken check valve spring.
Air bubbles in the lubrication system will prevent the valve tappet from supporting the valve spring load and can be caused by too high or too low an oil
level in the oil pan, or by air being drawn into the system through a hole, crack or leaking oil pump inlet tube gasket on the oil pump screen cover and
tube.
If the leak-down time is below the specified time for used valve tappets, noisy operation can result. If no other cause for noisy valve tappets can be
found, check the leak-down rate and replace any outside the specification.
Assembled valve tappets can be tested with Hydraulic Tappet Leak-Down Tester to check the leak-down rate. The leak-down rate specification is the
time in seconds for the plunger to move a specified distance of its travel while under a 22.7 kg (50 lb) load.
