Hummer H2. Manual - part 62

Fig. 7: Reaming Valve Guides 

Replacing Valve Guide 

 

1998 Chevrolet Pickup C1500 

GENERAL INFORMATION Engine Overhaul Procedures

  

Replace valve guide if clearance exceeds specification. Valve guides are either pressed, hammered or shrunk in 
place, depending upon cylinder head design and type of metal used.  

Remove valve guide from cylinder head by pressing or tapping on a stepped drift. See Fig. 8 . Once valve guide 
is installed, distance from cylinder head to top of valve guide must be checked. This distance must be within 
specification.  

Aluminum heads are often heated before installing valve guide. Valve guide is sometimes cooled in dry ice 
prior to installation. Combination of a heated cylinder head and cooled valve guide ensures a tight guide fit 
upon assembly. The new guide must be reamed to specification.  

Fig. 8: Typical Valve Guide Remover & Installer 

VALVES & VALVE SEATS 

Valve Grinding 

Valve stem O.D. should be measured in several areas to indicate amount of wear. Replace valve if not within 
specification. Valve margin area should be measured to ensure that valve can be ground. See Fig. 9 .  

If valve margin is less than specification, the valves will be burned. Valve must be replaced. Due to minimum 
margin dimensions during manufacture, some new type valves cannot be reground. Some manufacturers use 
stellite coated valves that must NOT be machined. Valves can only be lapped into valve seat.  

CAUTION: Some valves are sodium filled. Extreme care must be used when 

disposing of damaged or worn sodium-filled valves. 

 

1998 Chevrolet Pickup C1500 

GENERAL INFORMATION Engine Overhaul Procedures

  

Fig. 9: Measuring Valve Head Margin 

Resurface valve to proper angle specification using valve grinding machine. Follow manufacturer's instructions 
for valve grinding machine. Specifications may indicate a different valve face angle than seat angle. Measure 
valve margin after grinding. Replace valve if not within specification. Valve stem tip can be refinished using 
valve grinding machine.  

Valve Lapping 

During valve lapping of recently designed valves, be sure to follow manufacturer's recommendations. Surface 
hardening and materials used with some valves do not permit lapping. Lapping process will remove excessive 
amounts of the hardened surface.  

Valve lapping is done to ensure adequate sealing between valve face and seat. Use either a hand drill or lapping 
stick with suction cup attached.  

Moisten and attach suction cup to valve. Lubricate valve stem and guide. Apply a thin coat of fine valve 
grinding compound between valve and seat. Rotate lapping tool between the palms or with hand drill.  

Lift valve upward off the seat and change position often. This is done to prevent grooving of valve seat. Lap 
valve until a smooth polished seat is obtained. Thoroughly clean grinding compound from components. Valve-
to-valve seat concentricity should be checked. See VALVE SEAT CONCENTRICITY .  

Valve Seat Grinding 

CAUTION: Valve guides must be in good condition and free of carbon deposits prior 

to valve seat grinding. Some engines contain an induction hardened valve 
seat. Excessive material removal will damage valve seats. 

 

1998 Chevrolet Pickup C1500 

GENERAL INFORMATION Engine Overhaul Procedures

  

Select coarse stone of correct size and angle for seat to be ground. Ensure stone is true and has a smooth 
surface. Select correct size pilot for valve guide dimension. Install pilot in valve guide. Lightly lubricate pilot 
shaft. Install stone on pilot. Move stone off and on the seat approximately 2 times per second during grinding 
operation.  

Select a fine stone to finish grinding operation. Various angle grinding stones are used to center and narrow the 
valve seat as required. See Fig. 10 .  

Fig. 10: Adjusting Valve Seat Width 

Valve Seat Replacement 

Replacement of valve seat inserts is done by cutting out the old insert and machining an oversize insert bore. 
Replacement oversize insert is usually cooled and the cylinder head is sometimes warmed. Valve seat is pressed 
into the head. This operation requires specialized machine shop equipment.  

Valve Seat Concentricity 

Using dial gauge, install gauge pilot in valve guide. Position gauge arm on the valve seat. Adjust dial indicator 
to zero. Rotate arm 360 degrees and note reading. Runout should not exceed specification.  

To check valve-to-valve seat concentricity, coat valve face lightly with Prussian Blue dye. Install valve and 
rotate it on valve seat. If pattern is even and entire seat is coated at valve contact point, valve is concentric with 

 

1998 Chevrolet Pickup C1500 

GENERAL INFORMATION Engine Overhaul Procedures