Valve Guide Reaming

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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 1: Measuring Valve Stem-To-Guide Clearance Using A Dial Indicator
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 (4.8L, 5.3L, And 6.0L) Specifications (LR4 VIN V) or Engine Mechanical (4.8L, 5.3L, And 6.0L) Specifications (LM7 VIN T) or Engine Mechanical (4.8L, 5.3L, And 6.0L) Specifications (L59 VIN Z) or Engine Mechanical (4.8L, 5.3L, And 6.0L) Specifications (LQ4 VIN U) or Engine Mechanical (4.8L, 5.3L, And 6.0L) Specifications (LQ9 VIN N) .

Fig 2: Replacing Valve Stem & Guide With Excessive Clearance
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.
- A valve guide that is worn and has excessive stem-to-guide clearance should be reamed and valves with oversize stems installed.
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 valve guide must be reamed oversize and a valve with oversize stem installed.

Fig 3: Inspecting Valve Stems For Damage
Courtesy of GENERAL MOTORS CORP.
Ream the valve guide using the J 37378-1 .
Clean the guide bore of all metal shavings and debris.

Fig 4: Reaming Valve Guide Using J 37378-1
Courtesy of GENERAL MOTORS CORP.
Install the valve (2), with oversize stem, into the cylinder head (1).
Inspect the valve for the proper fit.
Move the valve back and forth in the guide. The valve should move freely with no resistance or drag.

Fig 5: Inspecting Valve For Proper Fit
Courtesy of GENERAL MOTORS CORP.