Cylinder Head Valve Guide Oil Leakage Analysis

Cylinder Head Model: Z20S

Leakage Location: Between valve stem and valve guide

Problem Description

Oil leakage occurs between the valve stem and the valve guide of the Z20S cylinder head. This area typically consists of the valve guide, valve stem seal, and valve stem. If sealing or fitment is improper, engine oil can travel upward along the valve stem, causing oil burning or external leakage.

Possible Causes Analysis

1. The valve stem seal is aged, hardened, worn, or improperly installed, resulting in oil leakage.

2. Excessive clearance between valve stem and guide due to wear or machining deviation allows oil to pass through.

3. Scratches or poor surface finish on the valve stem can damage the seal lip.

4. Incorrect seal size causes improper fit between guide and valve stem.

5. Improper assembly, lack of lubrication, or incorrect pressing depth can deform or tear the seal lip.

Inspection and Verification

1. Inspect the valve stem seal for aging, hardness, or lip damage.

2. Measure clearance between valve stem and guide (recommended: 0.02–0.05 mm).

3.Check valve stem for scratches or bending.

4. Ensure the seal is correctly seated, vertical, and undamaged.

Repair and Improvement Suggestions

1. Replace the valve stem seal with high-quality FKM material and use proper tools.

2. Replace valve guide or valve if clearance exceeds limits.

3. Apply lubricant to the valve stem during assembly to protect the seal.

4.  If the guide bore is out of tolerance, re-machine or replace the cylinder head.