Crown Victoria V8-281 4.6L SFI (1998)
Hydraulic Valve Tappets: Component Tests and General Diagnostics
Leakdown Test
1. Place valve tappet in tester with plunger facing upward. Pour hydraulic tester fluid into cup to a level that will cover valve tappet. The fluid can be
purchased from manufacturer of tester. Using kerosene or any other fluid will not provide an accurate test.
NOTE: Do not mix parts from different valve tappets. Parts are select-fitted and not interchangeable.
2. Place a 7.94 mm (0.312-inch) steel ball provided with tester in plunger cap.
NOTE: Valve tappets cannot be checked with engine oil in them. Only testing fluid can be used.
3. Adjust length of ram so that pointer is 1.59 mm (0.062 inch) below starting mark when ram contracts valve tappet plunger to facilitate timing as
pointer passes Start Timing mark.
Use center mark on pointer scale as Stop Ramming point instead of original Stop Ramming mark at top of scale.
4. Work valve tappet plunger up and down until valve tappet fills with fluid and all traces of air bubbles have disappeared.
5. Allow ram and weight to force valve tappet plunger downward. Measure exact time it takes for pointer to travel from Start Timing to Stop Timing
marks of tester.
6. A satisfactory valve tappet must have a leakdown rate (time in seconds) within minimum and maximum limits found under Specifications.
7. If valve tappet is not within specification' replace it with a new valve tappet. Do not disassemble and clean new valve tappets before testing
because oil contained in new valve tappets is test fluid.
8. Remove fluid from cup and bleed fluid from valve tappet by working plunger up and down. This step will aid in depressing valve tappet plungers
when checking valve clearance.
Noise
Hydraulic valve tappet noise may be caused by any of the following:
- excessive collapsed valve tappet gap.
- sticking valve tappet plunger.
- valve tappet check valve not functioning properly.
- air in lubrication system.
- leakdown rate too rapid.
- excessive valve guide wear.
Excessive collapsed valve tappet gap may be caused by a worn valve tappet, roller valve tappets or valve tip. With valve tappet collapsed, check gap
between valve tip and follower to determine if any other valve train parts are damaged, worn or out of adjustment.
A sticking valve tappet plunger may be caused by dirt, chips or varnish inside the valve tappet. Correct the sticking by replacing with a new valve tappet.
Air bubbles in the lubrication system will prevent the valve tappet from supporting the valve spring load and may be caused by too high or low an oil
level in the oil pan. It may also be caused by air drawn into the system through a hole, crack or leaking 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 may result. If no other cause for noisy valve tappets can be
found, the leak-down rate should be checked and any valve tappets outside the specification should be replaced.
Assembled valve tappets can be tested with a hydraulic tappet leakdown 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. Test the valve tappets with a hydraulic tappet
leakdown tester.
