Hummer H2. Manual - part 63

the valve seat.  

CYLINDER HEAD REASSEMBLY 

Valve Stem Installed Height 

Valve stem installed height must be checked when new valves are installed or when valves or valve seats have 
been ground. Install valve in valve guide. Measure distance from tip of valve stem to spring seat. See Fig. 11 . 
Distance must be within specification to allow sufficient clearance for valve operation.  

Remove valve and grind valve stem tip if height exceeds specification. Valve tips are surface hardened. DO 
NOT remove more than .010" (.25 mm) from tip. Chamfer sharp edge of reground valve tip. Recheck valve 
stem installed height.  

Fig. 11: Measuring Valve Stem Installed Height 

VALVE STEM OIL SEALS 

Valve stem oil seals must be installed on valve stem. See Fig. 2 . Seals are needed due to pressure differential at 
the ends of valve guides. Atmospheric pressure above intake guide, combined with manifold vacuum below 
guide, causes oil to be drawn into the cylinder.  

Exhaust guides also have pressure differential created by exhaust gas flowing past the guide, creating a low 
pressure area. This low pressure area draws oil into the exhaust system. 

 

1998 Chevrolet Pickup C1500 

GENERAL INFORMATION Engine Overhaul Procedures

  

Some manufacturers require that special color code or specified height valve stem oil seal be installed in 
designated area.  

Replacement (On-Vehicle) 

Mark rocker arm or overhead cam components for location. Remove rocker arm components or overhead cam 
components. Components must be installed in original location. Remove spark plugs. Valve stem oil seals may 
be replaced by holding valves against seats using air pressure.  

Air pressure must be installed in cylinder using an adapter for spark plug hole. An adapter can be constructed by 
welding air hose connection to spark plug body with porcelain removed.  

Rotate engine until piston is at top of stroke. Install adapter in spark plug hole. Apply a minimum of 140 psi 
(9.8 kg/cm 

2

 ) line pressure to adapter. Air pressure should hold valve closed. If air pressure does not hold valve 

closed, check for damaged or bent valve. Cylinder head must be removed for service.  

Using valve spring compressor, compress valve springs. Remove valve locks. Carefully release spring 
compressor. Remove retainer or rotator and valve spring. Remove valve stem oil seal.  

If oversize valves have been installed, oversize oil seals must be used. Coat valve stem with engine oil. Install 
protective sleeve over end of valve stem. Install new oil seal over valve stem and seat on valve guide. Remove 
protective sleeve. Install spring seat, valve spring and retainer or rotator. Compress spring and install valve 
locks. Remove spring compressor. Ensure valve locks are fully seated.  

Install rocker arms or overhead cam components. Tighten all bolts to specification. Adjust valves if required. 
Remove adapter. Install spark plugs, valve cover and gasket.  

VALVE SPRING INSTALLED HEIGHT 

Valve spring installed height should be checked during reassembly. Measure height from lower edge of valve 
spring to the upper edge. DO NOT include valve spring seat or retainer. Distance must be within specification. 
If valves and/or seats have been ground, a valve spring shim may be required to correct spring height. See Fig. 
12 .  

 

1998 Chevrolet Pickup C1500 

GENERAL INFORMATION Engine Overhaul Procedures

  

Fig. 12: Measuring Valve Spring Installed Height 

ROCKER ARMS & ASSEMBLIES 

Rocker Studs 

Rocker studs are either threaded or pressed in place. Threaded studs are removed by locking 2 nuts on the stud. 
Unscrew the stud by turning the jam nut. Coat new stud threads with Loctite and install. Tighten to 
specification.  

Pressed-in stud can be removed using a stud puller. Ream stud bore to proper specification and press in a new 
oversize stud. Pressed-in studs are often replaced by cutting threads in the stud bore to accept a threaded stud.  

Rocker Arms & Shafts 

Mark rocker arms for location. Remove rocker arm retaining bolts. Remove rocker arms. Inspect rocker arms, 
shafts, bushings and pivot balls (if equipped) for excessive wear. Inspect rocker arms for wear in valve stem 
contact area. Measure rocker arm bushing I.D. Replace bushings if excessively worn.  

The rocker arm valve stem contact point may be reground, using special fixture for valve grinding machine. 
Remove minimum amount of material as possible. Ensure all oil passages are clear. Install rocker arm 
components in original location. Ensure rocker arm is properly seated in push rod. Tighten bolts to 
specification. Adjust valves if required. See VALVE ADJUSTMENT .  

PUSH RODS 

Remove rocker arms. Mark push rods for location. Remove push rods. Push rods can be steel or aluminum, 
solid or hollow. Hollow push rods must be internally cleaned to ensure oil passage to rocker arms is cleaned. 
Check push rods for damage, such as loose ends on steel tipped aluminum types. 

 

1998 Chevrolet Pickup C1500 

GENERAL INFORMATION Engine Overhaul Procedures

  

Check push rod for straightness. Roll push rod on a flat surface. Using feeler gauge, check clearance at center. 
Replace push rod if bent. The push rod can also be supported at each end and rotated. A dial indicator is used to 
detect a bent area in the push rod.  

Lubricate ends of push rod and install push rod in original location. Ensure push rod is properly seated in lifter. 
Install rocker arm. Tighten bolts to specification. Adjust valves if required. See VALVE ADJUSTMENT .  

LIFTERS 

Hydraulic Lifters 

Before replacing a hydraulic lifter for noisy operation, ensure noise is not caused by worn rocker arms or valve 
tips. Also ensure sufficient oil pressure exists. Hydraulic lifters must be installed in original location. Remove 
rocker arm assembly and push rod. Mark components for location. Some applications require intake manifold, 
cylinder head or lifter cover removal. Remove lifter retainer plate (if used). To remove lifters, use a hydraulic 
lifter remover or magnet. Different type lifters are used. See Fig. 13 .  

On sticking lifters, disassemble and clean lifter. DO NOT mix lifter components or positions. Parts are select-
fitted and are not interchangeable. Inspect all components for wear. Note amount of wear in lifter body-to-
camshaft contact area. Surface must have smooth and convex contact face. If wear is apparent, carefully inspect 
cam lobe.  

Inspect push rod contact area and lifter body for scoring or signs of wear. If body is scored, inspect lifter bore 
for damage and lack of lubrication. On roller type lifters, inspect roller for flaking, pitting, loss of needle 
bearings and roughness during rotation.  

Measure lifter body O.D. in several areas. Measure lifter bore I.D. Ensure components or oil clearance is within 
specification. Some models offer oversize lifters. Replace lifter if damaged.  

If lifter check valve is not operating, obstructions may be preventing it from closing or valve spring may be 
broken. Clean or replace components as necessary.  

Check plunger operation. Plunger should drop to bottom of the body by its own weight when assembled dry. If 
plunger is not free, soak lifter in solvent to dissolve deposits.  

Lifter leak-down test can be performed on lifter. Lifter must be filled with special test oil. New lifters contain 
special test oil. Using lifter leak-down tester, perform leak-down test following manufacturer's instructions. If 
leak-down time is not within specifications, replace lifter assembly.  

Lifters should be soaked in clean engine oil several hours prior to installation. Coat lifter base, roller (if 
equipped) and lifter body with ample amount of Molykote or camshaft lubricant. See Fig. 13 . Install lifter in 
original location. Install remaining components. Valve lash adjustment is not required on most hydraulic lifters. 
Preload of hydraulic lifter is automatic. Some models may require adjustment.  

NOTE:

Some manufacturers require that a crankcase conditioner be added to engine 
oil and engine operated for specified amount of time to aid in lifter break-in 
procedure if new lifters or camshaft are installed. 

 

1998 Chevrolet Pickup C1500 

GENERAL INFORMATION Engine Overhaul Procedures