Chevrolet Silverado / GMC Sierra. Manual - part 370
1. Inspect the valve for the following conditions:
Burnt or eroded areas (1)
A worn margin (2)
A bent stem (3)
A worn or scored stem (4)
A worn key groove (5)
IMPORTANT:
Reconditioning the valve seats is very important. The
seating of the valves must be perfect for the engine to
deliver optimum power and performance. Several
different types of equipment are available for grinding
valve seats.
Another important factor is the cooling of the valve head.
Good contact between the valve and the seat will ensure
that heat will be properly dissipated.
The recommendations of the equipment manufacturer
should be followed carefully to obtain the proper results.
Regardless of the type of equipment used, it is essential
that valve guide bores be free of carbon or dirt to ensure
proper centering of the tool pilot in the guide.
Valves that are pitted must be refaced to the proper
angle. Valve stems that show excessive wear, or valves
that are warped excessively must be replaced. When a
valve head that is warped excessively is refaced, a knife
edge may be ground on part or all of the valve head due
to the amount of metal that must be removed. Knife
edges lead to breakage, burning or pre-ignition due to
heat localizing on this knife edge. If the edge of the valve
head is less than 1.25 mm (0.05 in) after grinding,
replace the valve.
Several different types of equipment are available for
refacing valves. The recommendation of the equipment
manufacturer should be carefully followed to obtain the
proper results.
DO NOT reface intake valves. Intake valves with
excessive wear or damage MUST be replaced.
2008 Hummer H2
2008 ENGINE Engine Mechanical - 6.2L - H2
A worn stem tip (6)
Fig. 482: Inspecting Valve Face For Burning, Pitting & Cracking
Courtesy of GENERAL MOTORS CORP.
2. Inspect the valve face for the following conditions:
Worn or no margin (1 or 4)
2008 Hummer H2
2008 ENGINE Engine Mechanical - 6.2L - H2
Pitted surfaces (2)
Burnt or eroded areas (3)
Fig. 483: Inspecting Valve Margin
Courtesy of GENERAL MOTORS CORP.
2008 Hummer H2
2008 ENGINE Engine Mechanical - 6.2L - H2
3. Inspect the valve margin.
The exhaust valve may be refaced if the margin is greater than 1.25 mm (0.05 in) thick
before grinding.
4. Reface pitted exhaust valves on a suitable valve refacing machine.
5. Replace the valve if the margin is less than 1.25 mm (0.05 in) thick after grinding.
6. If the valve face has been ground, it may be necessary to shim the valve spring in order to
obtain the proper spring installed height. Refer to Cylinder Head Disassemble.
7. Inspect for a loose valve seat in the cylinder head. The valve seat has an interference fit to
the cylinder head.
8. Clean the valve guide bores with a suitable tool. Remove all carbon or dirt from the bores.
The valve guide must be clean for the seat grinding tool to obtain proper results.
9. Grind the valve seat.
The recommendations of the equipment manufacturer should be followed carefully to obtain
the proper results. Regardless of the type of equipment used, it is essential that valve guide
bores be free from carbon or dirt to ensure proper centering of the tool pilot in the guide.
10. Inspect the valve seats.
The valve seats should be concentric to within 0.05 mm (0.0021 in) total indicator
reading.
If the valve seat has been ground, it may be necessary to shim the valve spring in order
to attain the proper spring installed height. Refer to Cylinder Head Disassemble.
CYLINDER HEAD ASSEMBLE
Tools Required
J 8062 Valve Spring Compressor - Head Off. See Special Tools.
Assemble
2008 Hummer H2
2008 ENGINE Engine Mechanical - 6.2L - H2