GM 6.5L V8 – Valve Train

The valve train includes the following parts (refer to Figure 2-21):
• Sixteen hydraulic roller lifters, positioned in cylinder case bores by guide plates and clamps
• A push rod for each lifter that provides mechanical movement and the transfer of lubricating oil to a rocker arm
• Four rocker arm assemblies, each containing a shaft with an intake and exhaust valve rocker arm for two cylinders
• Eight intake valve assemblies, each including an oil seal, return spring, two-piece stem retainer and a spring retainer
• Eight exhaust valve assemblies, each including two oil seals, a return spring, a two-piece stem retainer and a spring retainer/rotator

Each hydraulic roller lifter is an assembly of parts (see Figure 2-22, view A). Lifter operation transfers rotary camshaft motion to the upward and downward motion of the push rod, providing a hydraulic cushion (see Figure 2-22, views B and C).

When the camshaft lobe is not pushing upward, the lifter allows oil under lubrication system pressure to move through an internal plunger and past a check ball. As the camshaft lobe pushes the lifter body upward, oil is trapped under the plunger by the check ball, transferring force from the lifter body to the plunger and push rod seat. During its operation, each lifter pumps oil through its mating push rod, giving lubrication to the rocker arm and upper cylinder head parts.

The hydraulic lifters use guides to keep them from rotating (see Figure 2-23). Each guide positions two lifters, and
a bolt-in clamp holds each pair of guides in place. For the entire engine, eight guides and four clamps are used.

The lifter installation procedure has the following critical steps:
1. Coat the roller (and its bearing) of each lifter with a special extreme-pressure lubricant (GM P/N 1052365).
2. Install each lifter in its bore in the cylinder case.
3. Install each guide, rotating the lifters to align with it.
4. Install each clamp, aligning its ends with the center holes of each guide.
5. Tighten each clamp bolt to 26 N-m (19 Ib-ft) torque.
6. Manually rotate the crankshaft two complete revolutions (720 degrees of rotation) to check for binding.

Each push rod is a hollow steel tube with hollow metal balls welded to each end. One push rod ball end has greater hardness (identified by a paint stripe on the tube) and contacts a rocker arm. The other ball end rests in a seat of the hydraulic roller lifter.

Four stamped steel rocker arms are assembled to a hollow steel shaft and are located by press-in nylon buttons (see Figure 2-24). Rocker arms are identical for either the intake or exhaust valve position for each cylinder.

Two bolts hold each rocker arm assembly to the cylinder head, using specially shaped washers. Each cylinder head has two rocker arm assemblies.

The positions of the pistons must not be close to the valves during rocker arm installation. If any of the hydraulic lifters are full of oil, installing a rocker arm assembly may cause the lifter to push its valve into the face of a piston unless certain precautions are taken.

The procedure for installing a rocker arm assembly has these steps:
1. Rotate the crankshaft so that the torsional damper mark aligns with the TDC mark of the timing bracket on the
front cover.
2. Rotate the crankshaft in a counterclockwise direction so that the torsional damper mark moves a distance of
31/2 in. (see Figure 2-25).
3. Evenly tighten the two mounting bolts for each rocker arm assembly.
4. Tighten the rocker arm mounting bolts to 55 N-m (40 Ib-ft) torque.

The intake and exhaust valve assemblies have the parts shown in Figures 2-26 and 2-27. Each intake and exhaust valve slides in a guide bore machined in the cylinder head. Its valve face contacts a seat surface of the cylinder head that has been hardened by electric induction heating.

Both intake and exhaust valves use the same return spring assemblies, consisting of inner and outer coils designed to dampen vibration caused by high-speed valve operation. A metal washer positioned under each return spring prevents cylinder head surface wear.

Each intake and exhaust valve stem has a square-cut seal ring, and the exhaust valve also uses a lip-type seal mounted on the upper end of the valve guide. An intake valve uses a spring retainer with two valve stem keepers, while an exhaust valve has a rotator with its two keepers.

Valve service includes procedures for minor machining of the valve face and seat surfaces. Valve guide repair involves reaming guides to an oversize bore dimension and using new valves with an oversize stem diameter.

Valve train operation relates to the following diagnosis hints:

Condition #1: Momentary noise after engine is started
Cause: Oil drains from the lifters that are holding valves open when the engine is not running
Correction: None, since the condition is normal.

Condition #2: Intermittent noise at engine idle speed (disappearing when engine speed is increased)
Cause: Check ball inside one or more lifters is pitted or dirty
Correction: Clean or replace suspect lifter(s) – refer to Figure 2-28.

Condition #3: Noise at slow idle or with hot engine oil (quiet when engine speed is increased or with hot engine oil)
Cause: One or more lifters has a high leakdown rate
Correction: Replace suspect lifter(s).

Condition #4: Noise at high engine speed (quiet when engine speed is low)
A. High engine oil level (causing oil foaming)
B. Low engine oil level (causing oil aeration)
C. Oil pan bent or oil pump pick-up damaged
A. Drain engine oil to correct level.
B. Fill engine oil to correct level.
C. Repair or replace oil pan or oil pump.

Condition #5: Noise at engine idle speed (increasing in level as engine speed increases to 1500 rpm)
A. Badly worn or scuffed valve tip/rocker arm
B. Excessive valve stem-to-guide clearance
C. Excessive valve seat run-out
D. Valve spring that is off-square
E. Excessive valve face run-out
F. Valve spring clicking on rotator
A. Replace suspect parts.
B. Check and correct valve stem-to-guide clearance.
C. Machine valve seat(s) or replace cylinder head.
D. Check and replace suspect valve spring(s) – refer to Figure 2 -2 9 .
E. Machine or replace valve(s).
F. Rotate valve spring.

Condition #6: Noise at all engine speeds
A. Foreign particles in one or more valve lifters
B. Excessive valve lash
A. Clean suspect valve train part(s).
B. Check the following valve train parts for wear:
• Push rods (check lubrication)
• Rocker arms/shafts (check lubrication)
• Lifters (sticking plungers or internal wear)

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