Chevrolet Silverado / GMC Sierra. Service manual — part 369

1. Using a dial indicator, measure the valve stem-to-guide clearance. Position the tip of the dial

indicator at the top of the valve guide.

Valve stem-to-guide clearance may also be obtained by using a micrometer to measure the
valve stem diameter and a ball type measuring gage to measure the guide bore.

NOTE:

Excessive valve stem-to-guide clearance may cause a noisy
valve train, premature valve stem oil seal wear, component
damage, and/or excessive engine oil consumption.

NOTE:

Insufficient valve stem-to-guide clearance will result in noisy
or sticking valves. Valves that are too tight may disturb engine
smoothness or lead to component damage.

2008 Hummer H2

2008 ENGINE Engine Mechanical - 6.2L - H2

Fig. 479: Inspecting For Excessive Valve Stem To Guide Clearance
Courtesy of GENERAL MOTORS CORP.

2. A valve stem (1) and guide (2), with excessive clearance, must be replaced or the cylinder

head replaced. Refer to Engine Mechanical Specifications.

2008 Hummer H2

2008 ENGINE Engine Mechanical - 6.2L - H2

Fig. 480: Identifying Inspection Points For Valves Damage
Courtesy of GENERAL MOTORS CORP.

3. Inspect the valve stems for excessive scoring, wear, or warpage.

A valve stem that has excessive scoring (3 or 4) or wear (4 or 6) must be replaced.

If a valve guide is worn or has excessive stem-to-guide clearance, the cylinder head
should be replaced.

4. Measure the valve stem diameter. A valve stem with a diameter less than 7.95 mm (0.313 in)

2008 Hummer H2

2008 ENGINE Engine Mechanical - 6.2L - H2

must be replaced.

If the valve stem diameter is within specifications, and the stem-to-guide clearance is
excessive, the cylinder head must be replaced.

Valve and Seat Grinding

Fig. 481: Identifying Inspection Points For Valves Damage
Courtesy of GENERAL MOTORS CORP.

2008 Hummer H2

2008 ENGINE Engine Mechanical - 6.2L - H2