Valve Guide Reaming

WARNING: This page is about a different variant/trim than selected.

Fig 1: Measuring Valve Stem-To-Guide Clearance

Courtesy of GENERAL MOTORS CORP.

IMPORTANT:

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.
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.

Measure the valve stem-to-guide clearance using a dial indicator. 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.

Fig 2: Inspecting For Excessive Valve Stem To Guide Clearance

Courtesy of GENERAL MOTORS CORP.

A valve stem (1) and guide (2) with excessive clearance must be replaced or the components replaced. Refer to Engine Mechanical Specifications (LR4 VIN V) or Engine Mechanical Specifications (LM7 VIN T) or Engine Mechanical Specifications (LQ4 VIN U) .

Fig 3: Identifying Inspection Points For Valves Damage

Courtesy of GENERAL MOTORS CORP.

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