Viper V10-488 8.0L (1992)
Hydraulic Lash Adjuster: Testing and Inspection
GENERAL INFORMATION
The valve train includes roller tappet assemblies, aligning yokes and yoke retainer. Roller tappet alignment is maintained by machined flats on
tappet body being fitted in pairs into ten aligning yokes. The yokes are secured by a self contained screw and washer assembly.
PRELIMINARY STEP TO CHECKING THE HYDRAULIC TAPPETS
Before disassembling any part of the engine to correct tappet noise, read the oil pressure at the gauge. Install a reliable gauge at pressure sending
unit and check the oil level in the oil pan. The pressure should be between 30 to 80 psi (206.8 to 551.6 kPa) at 2000 rpm. The oil level in the pan
should never be above the MAX mark on dipstick, or below the MIN mark. Either of these two conditions could be responsible for noisy tappets.
Oil Level Check: stop engine after reaching normal operating temperature. Allow 5 minutes to stabilize oil level, check dipstick.
Oil Level Too High
If oil level is above the MAX mark on dipstick, it is possible for the connecting rods to dip into the oil while engine is running and create foam.
Foam in oil pan would be fed to the hydraulic tappets by the oil pump causing them to become soft and allow valves to seat noisily.
Oil Level Too Low
Low oil level may allow pump to take in air which when fed to the tappets, causes them to become soft and allows valves to seat noisily. Any leaks
on intake side of pump through which air can be drawn will create the same tappet action. Check the lubrication system from the intake strainer to
the pump cover, including the relief valve retainer cap. When tappet noise is due to aeration, it may be intermittent or constant, and usually more
than one tappet will be noisy. When oil level and leaks have been corrected, engine should be operated at fast idle to allow all of the air inside of
the tappets to be bled out.
VALVE TRAIN NOISE DIAGNOSIS
To determine source of valve train noise, operate engine at idle with cylinder head covers removed and listen for source of the noise.
NOTE: Worn valve guides or cocked springs are sometimes mistaken for noisy tappets. If such is the case, noise may be dampened by applying
side thrust on the valve spring. If noise is not appreciably reduced, it can be assumed the noise is in the tappet. Inspect the rocker arm push rod
sockets and push rod ends for wear.
Valve tappet noise ranges from light noise to a heavy click. A light noise is usually caused by excessive leak-down around the unit plunger which
will necessitate replacing the tappet, or by the plunger partially sticking in the tappet body cylinder. A heavy click is caused either by a tappet
check valve not seating, or by foreign particles becoming wedged between the plunger and the tappet body causing the plunger to stick in the down
position. This heavy click will be accompanied by excessive clearance between the valve stem and rocker arm as valve closes. In either case,
tappet assembly should be removed for inspection and cleaning.
