Valve Guide Reaming

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.

Fig 1: Measuring Valve Stem-To-Guide Clearance

Courtesy of GENERAL MOTORS CORP.

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

Fig 2: Inspecting For Excessive Valve Stem To Guide Clearance
Courtesy of GENERAL MOTORS CORP.

Refer to Engine Mechanical Specifications (LR4 VIN V) or Engine Mechanical Specifications (LM7 VIN T) or Engine Mechanical Specifications (L33 VIN B) or Engine Mechanical Specifications (L59 VIN Z) or Engine Mechanical Specifications (LQ4 VIN U) or Engine Mechanical Specifications (LQ9 VIN N) .
Inspect the valve stems for excessive scoring, wear, or warpage.

Fig 3: Identifying Inspection Points For Valves Damage
Courtesy of GENERAL MOTORS CORP.

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.