Hydraulic Valve Tappet

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
- worn adjustment shims
- worn cam follower
- worn cam follower bores

Excessive collapsed valve tappet gap may be caused by loose rocker arm seat bolts, incorrect initial adjustment, or wear of valve tappet face, roller valve tappets, push rods, rocker arms, rocker arm seat or valve tip. With valve tappet collapsed, check gap between valve tip and rocker arm and/or camshaft lobe (depending upon application) to determine if any other valve train parts are damaged, worn or out of adjustment.

A sticking hydraulic valve tappet plunger may be caused by dirt, chips or varnish inside the valve tappet. The sticking can be corrected by disassembling the valve tappet and removing the debris causing the condition.

A hydraulic valve tappet check valve that is not functioning may be caused by an obstruction such as dirt or chips that prevent it from closing when the cam lobe is lifting the valve tappet. It may 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 may be caused by too high or low of an oil level in the oil pan. It may also be caused by air being drawn into the system through a hole, crack or leaking O-rings on the oil pump screen cover and tube.

If the Leakdown time is below the specified time for used hydraulic valve tappets, noise may result. If no other cause for noisy hydraulic valve tappets can be found, check the Leakdown rate and replace any hydraulic valve tappets outside the specification.

Test the assembled hydraulic valve tappets with a Hydraulic Tappet Leakdown Tester to check the Leakdown rate. The Leakdown rate specification is the time in seconds for the plunger to move a specified distance while under a 22.7 kg (50 lb) load. Test the valve tappet as follows:

LEAKDOWN TESTING
1. Disassemble and clean the hydraulic valve tappet to remove all traces of engine oil.

NOTE: Do not mix parts from different hydraulic valve tappets. Parts are select-fitted and not interchangeable.

2. Place hydraulic valve tappet in tester with plunger facing upward. Pour hydraulic tester fluid into cup to a level that will cover hydraulic valve tappet. The fluid can be purchased from the tester's manufacturer. Using kerosene or any other fluid will not provide an accurate test.

NOTE: Hydraulic valve tappets cannot be checked with engine oil in them. Use only the testing fluid.

3. Place 7.94 mm (5/16-inch) steel ball provided with tester in plunger cap.
4. Adjust length of ram so pointer is 1.59 mm (1/16 inch) below starting mark when ram contacts valve tappet plunger to facilitate timing as pointer passes the Start Timing mark.

Use the center mark on the pointer scale as Stop Timing point instead of the original Stop Timing mark at top of scale.

5. Work valve tappet plunger up and down until hydraulic valve tappet fills with fluid and all traces of air bubbles have disappeared.
6. Allow ram and weight to force hydraulic valve tappet plunger downward. Measure exact time it takes for pointer to travel from Start Timing to the Stop Timing marks of tester.
7. A satisfactory hydraulic valve tappet must have a Leakdown rate (time in seconds) within specified minimum and maximum limits.
8. If hydraulic valve tappet is not within specification, replace it with new hydraulic valve tappet. Do not disassemble and clean new hydraulic valve tappets before testing because oil contained in new hydraulic valve tappets is test fluid.
9. Remove fluid from cup and bleed fluid from hydraulic valve tappet by working plunger up and down. This step will aid in depressing tappet plungers when checking valve clearance.