Camshaft Lobe Lift

Check the lift of each lobe in consecutive order and make a note of the readings.

1. Remove valve covers (6582) .

2. Remove rocker arm bolts, rocker arm seat (6A528) and rocker arm (6564) .

3. Ensure valve tappet (6500) is seated against camshaft (6250) . Install Rotunda Dial Indicator with Bracketry 014-00282 or equivalent in such a manner as to have ball socket adapter of indicator on top of valve tappet , or Cup Shaped Adapter TOOL-6565-AB or equivalent on top of push rod (6565) and in same plane as valve tappet or push rod movement.

4. Remove spark plugs (12405) .

5. Connect an auxiliary starter switch in starting circuit. Crank engine with ignition switch (11572) in OFF position. "Bump" crankshaft (6303) over until valve tappet is on base circle of camshaft lobe. At this point, valve tappet will be in its lowest position. If checking during assembly of engine, turn crankshaft using a socket or ratchet.

6. Zero dial indicator. Continue to rotate crankshaft slowly until valve tappet is in fully-raised position (highest indicator reading).

7. Compare total lift recorded on indicator with specifications.

8. To check accuracy of original indicator reading, continue to rotate crankshaft until indicator reads zero.

   NOTE: If lift on any lobe is below specified service limits, camshaft and valve tappet operating on worn lobe(s) must be replaced, as well as any valve tappet showing pitting or having contact face worn flat or concave. Refer to Inspection, Camshaft and Hydraulic Valve Tappets.

9. Remove dial indicator, adapter and auxiliary starter switch.

    CAUTION: After installing rocker arms , do not rotate crankshaft until valve tappets have had sufficient time to bleed down. To do otherwise may cause serious valve damage. Manually bleeding down will reduce waiting time.

10. Install valve covers .

11. Install spark plugs .

Hydraulic Valve Tappet

Hydraulic valve tappet noise may be caused by any of the following:

1. Excessive collapsed valve tappet gap.

2. Sticking valve tappet plunger.

3. Valve tappet check valve not functioning properly.

4. Air in lubrication system.

5. Leakdown rate too rapid.

6. Excessive valve guide wear.

   Excessive collapsed valve tappet gap may be caused by loose rocker arm bolts/nuts, incorrect initial adjustment, or wear of valve tappet face, or worn roller valve tappets , push rods , rocker arm seat or valve tip. With valve tappet collapsed, check gap between valve tip and rocker arm 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 . The sticking can be corrected by disassembling the valve tappet and removing the dirt, chips or varnish that are causing the condition.

   A valve tappet check valve that is not functional may be caused by an obstruction such as dirt or chips preventing it from closing when the camshaft lobe is lifting the valve tappet , or it may 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. This may be caused by too high or too low an oil level in the oil pan (6675) , or by air being drawn into the system through a hole, crack or leaking gasket on the oil level indicator tube (6754) .

   If the leakdown 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 leakdown rate should be checked and any outside the specification should be replaced.

   Assembled valve tappets can be tested with Hydraulic Tappet Leakdown Tester TOOL-6500-E or equivalent 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 tappets as follows:

Leakdown Testing

1. Disassemble and clean valve tappet to remove all traces of engine oil.

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

   NOTE: Valve tappets cannot be checked with engine oil in them. Only testing fluid can be used.

2. 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.

3. Place a 7.94mm (5/16 inch) steel ball provided with tester in plunger cap.
   
   
   
   

4. Adjust length of ram so that pointer is 1.59mm (1/16 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 Timing point instead of original Stop Timing mark at top of scale.

5. Work valve tappet plunger up and down until valve tappet fills with fluid and all traces of air bubbles have disappeared.

6. 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.

7. A valve tappet that is satisfactory must have a leakdown rate (time in seconds) within minimum and maximum limits specified.

8. If valve tappet is not within specification, replace it with a new valve tappet . If a worn flat valve tappet is replaced with a new valve tappet , it is recommended that a new camshaft be installed. It is not necessary to disassemble and clean new valve tappets before testing because oil contained in new valve tappets is test fluid.

9. 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.