Valve Train Analysis

Valve Train Analysis-Engine Off-Valve Cover Removed
Check for damaged or severely worn parts and correct assembly. Make sure correct parts are used with the static engine analysis as follows.

Valve Train Analysis-Engine Off, Rocker Arm
^ Check for loose mounting bolts, studs and nuts.
^ Check for plugged oil feed in the rocker arms or cylinder head.

Valve Train Analysis-Engine Off, Camshaft Roller Followers and Hydraulic Lash Adjusters, Overhead Camshaft
^ Check for loose mounting bolts on camshaft carriers.
^ Check for plugged oil feed in the camshaft roller followers, lash adjusters or cylinder heads.

Valve Train Analysis-Engine Off, Camshaft-Engines
^ Check for broken or damaged parts.

Valve Train Analysis-Engine Off, Push Rods
^ Check for bent push rods and restricted oil passage.

Valve Train Analysis-Valve Springs
^ Check for broken or damaged parts.

Valve Train Analysis-Engine Off, Valve Spring Retainer and Valve Spring Retainer Keys

^ Check for correct seating of the valve spring retainer key on the valve stem and in valve spring retainer.
^ Check for correct seating on the valve stem.

Valve Train Analysis-Engine Off, Valves and Cylinder Head
^ Check for plugged oil drain back holes.
^ Check for worn or damaged valve tips.
^ Check for missing or damaged guide-mounted valve stem seal.
^ Check collapsed valve tappet gap.
^ Check installed valve spring height.
^ Check for missing or worn valve spring seats.
^ Check for plugged oil metering orifice in cylinder head oil reservoir (if equipped).

Static checks (engine off) are to be made on the engine prior to the dynamic procedure.

Valve Train Analysis-Engine Running
^ Start the engine and, while idling, check for correct operation of all parts. Check the following:

Valve Train Analysis-Engine Running, Valves and Cylinder Head
^ Check for plugged oil drain back holes.
^ Check for missing or damaged valve stem seals or guide mounted valve stem seals.
^ Check for a plugged oil metering orifice in the cylinder head oil reservoir (4.6L engine only).

If insufficient oiling is suspected, check oil passages for blockage, then accelerate the engine to 1,200 rpm with the transmission in NEUTRAL and the engine at normal operating temperature. Oil should spurt from the rocker arm oil holes such that valve tips and camshaft roller followers are well oiled. With the valve covers off, some oil splash may overshoot camshaft roller followers.

Valve Train Analysis-Engine Running, Camshaft Lobe Lift-OHC Engines
Check the lift of each camshaft lobe in consecutive order and make a note of the readings.
1. Remove the valve covers.
2. Remove the spark plugs.
3. Install the Dial Indicator Gauge with Holding Fixture so the rounded tip of indicator is on top of the camshaft lobe and on the same plane as the valve tappet.





4. Rotate the crankshaft using a breaker bar and socket attached to the crankshaft pulley retainer bolt. Rotate the crankshaft until the base circle of the camshaft lobe is reached.
5. Zero the dial indicator. Continue to rotate the crankshaft until the (1) high-lift point of the camshaft lobe is in the fully-raised position (highest indicator reading).
6. To check the accuracy of the original indicator reading, continue to rotate crankshaft until the (2) base circle is reached. The indicator reading, should be zero. If zero reading is not obtained. repeat Steps 1 through 6.

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

Remove the Dial Indicator Gauge with Holding Fixture.
8. Install the spark plugs.
9. Install the valve covers.

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.
3. Make sure the valve tappet is seated against 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 push rod and in same plane as valve tappet push rod movement.
4. Remove the spark plugs.
5. Connect an auxiliary starter switch in the starting circuit. Crank the engine with ignition switch in OFF position. Bump crankshaft 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 engine assembly, turn crankshaft using a socket or ratchet.
6. Zero the dial indicator. Continue to rotate crankshaft slowly until 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 rocker arm seats, rocker arms and rocker arm seat bolts.
9. Install valve covers.
10. Install 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 valve tappet face, or worn roller valve tappets, push rod, rocker arm, rocker arm seat or valve tip. With valve tappet collapsed, check 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 leakdown time out of specification can cause tappet noise. If no other cause for noisy valve tappets can be found, the leakdown rate should be checked and new valve tappets installed if found to be out of specification.

Assembled valve tappets can be tested with 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 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.