Chevrolet Silverado / GMC Sierra. Service manual — part 583

Fig. 19: Measuring Valve Stem To Guide Clearance
Courtesy of GENERAL MOTORS CORP.

12. If the valve stem to guide clearance is over 0.25 mm (0.098 in) for the exhaust valve guides

or 0.20 mm (0.0079 in) for the intake valve guides, the cylinder head must be replaced.

13. Inspect the valves for the following:

Bent valve stem

Scored valve stem

Worn valve key grooves

Pitted surfaces

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Mechanical - 6.6L - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

Fig. 20: Measuring Valve Margin
Courtesy of GENERAL MOTORS CORP.

14. Measure the valve margin. The intake valve production margin is 1.2 mm (0.0472 in) and

the service limit is 0.88 mm (0.0346 in). The exhaust valve production margin is 1.0 mm
(0.0394 in) and the service limit is 0.73 mm (0.0287 in). Replace the valve if the valve
margin is below the service limit.

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Mechanical - 6.6L - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

Fig. 21: Measuring Valve Depression
Courtesy of GENERAL MOTORS CORP.

15. Measure the valve depression.

1. Insert a new valve into the cylinder head (1).

2. Use a depth gage or a straight edge to measure the valve depression from the cylinder

head gasket surface (2). The intake valve depression is 0.6 mm (0.0236 in) and the
service limit is 2.5 mm (0.0984 in). The exhaust valve depression is 0.9 mm (0.0354
in) and the service limit is 2.0 mm (0.0787 in). Recondition the valve seat if the valve
depression is above specifications.

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Mechanical - 6.6L - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

Fig. 22: Measuring Valve Contact Width
Courtesy of GENERAL MOTORS CORP.

16. Measure the valve contact width.

Inspect the valve contact area for roughness or unevenness.

The intake valve contact width is 2.1 mm (0.0827 in) and the service limit is 2.5 mm
(0.0984 in).

The exhaust valve contact width is 2.1 mm (0.0827 in) and the service limit is 2.5 mm
(0.0984 in).

Recondition the valve seats to bring the contact width into specifications.

VALVE AND SEAT GRINDING

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Mechanical - 6.6L - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado