Valve Train Diagnosis

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, 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 - Valve Springs
^ Check for broken or damaged parts.

Valve Train Analysis - Engine Off, Valve Spring Retainer and Valve Spring Retainer Keys
^ Check for proper seating of the valve spring retainer key on the valve stem and in valve spring retainer.
^ Check for proper 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 proper operation of all parts. Check the following:

Valve Train Analysis - Engine Running, Positive Rotator and Valve Spring Retainer Keys
^ Check for proper operation of positive rotator.

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 1200 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 with Bracketry 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 (A) 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 (B) 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, the camshaft roller followers operating on that camshaft must be replaced.

Remove the Dial Indicator with Bracketry.
8. Install the spark plugs.
9. Install the valve covers.

Valve Train Analysis - Engine Running, Valve Tappet
Valve tappet noise can 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 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.
A sticking valve tappet plunger can be caused by contaminants or varnish inside the valve tappet.
A valve tappet check valve that is not functioning can be caused by an obstruction such as dirt or chips that prevent it from closing when the camshaft 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. 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.
If the leakdown time is below the specified time for used valve tappets, noisy operation can result. If no other cause for noisy valve tappets can be found, the leakdown rate should be checked and any valve tappets outside the specification should be replaced.
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 lb) load. Test the valve tappets.