Valve Train Analysis - Engine Running, Camshaft Lobe Lift - Push Rod Engine

Valve Train Analysis - Engine Running, Camshaft Lobe Lift - Push Rod Engine
Check the lift of each lobe in consecutive order and make a note of the readings.
1. Remove the valve covers.
2. Remove the rocker arm seat bolts, rocker arm seat and rocker arms.
Typical Engine With Push Rods

Typical Engine With Push Rods:

3. Make sure the valve tappet is seated against the camshaft. Install (1) Dial Indicator Gauge with Holding Fixture so the ball socket adapter of the indicator is on top of the valve tappet or (2) Dial Indicator Gauge Adapter is on top of the push rod and in the same plane as the valve tappet push rod movement.
4. Remove the spark plugs.
5. Connect an auxiliary starter switch in the starting circuit. Crank the engine with the ignition switch in the OFF position. Bump the crankshaft over until the valve tappet is on the base circle of the camshaft lobe. At this point, the valve tappet will be in its lowest position. If checking during engine assembly, turn the crankshaft using a socket or ratchet.
6. Zero the dial indicator. Continue to rotate the crankshaft slowly until the valve tappet is in fully-raised position (highest indicator reading).

7. NOTE: If lift on any lobe is below specified service limits, install a new camshaft, and new valve tappets.

Remove the Dial Indicator with Holding Fixture, Dial Indicator Gauge Adapter and auxiliary starter switch.
8. Install the rocker arm seats, the rocker arms and the rocker arm seat bolts.
9. Install the valve covers.
10. Install the spark plugs.

Valve Train Analysis - Engine Running, Valve Tappet
Valve tappet noise can be caused by any of the following:
^ Excessive valve tappet gap (collapsed)
^ Incorrectly functioning valve tappet
^ Air in lubrication system
^ Excessive valve guide wear
^ Low oil pressure

Excessive collapsed valve tappet gap can be caused by loose rocker arm seat bolts/nuts, incorrect initial adjustment or wear of the valve tappet face, or worn roller valve tappets, push rod, rocker arm, rocker arm seat or valve tip. With the valve tappet collapsed, check the gap between the valve tip and the rocker arm to determine if any other valve train parts are damaged, worn or out of adjustment.

An incorrectly functioning valve tappet can be sticking, caused by contaminants or varnish inside the tappet. The tappet can have a check valve that is not functioning correctly, which can be caused by an obstruction, such as dirt or chips that prevent the check valve from closing, or a broken check valve spring. A tappet with a leak-down time out of specification can cause tappet noise. If no other cause for noisy valve tappets can be found, the leak-down rate should be checked and new valve tappets installed if found to be out of specification.

Assembled valve tappets can be tested with Hydraulic Lash Adjuster 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 while under a 22.7 kg (50 lbs.) load.

Air bubbles in the lubrication system will prevent the valve tappet from supporting the valve spring load. This 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 gasket on the oil pump screen cover and tube.