During durability testing of an engine cylinder block assembly, oil seepage was observed at the main oil passage plug after 8 hours of operation. This study investigates the root cause through thermal expansion analysis and material characterization while proposing an optimized sealing solution.
Thermal Expansion Analysis
The differential thermal expansion between the cast iron engine cylinder block (α = 23×10-6/°C) and steel oil plug (α = 12×10-6/°C) creates critical interfacial gaps. The linear expansion equation:
$$
\Delta L = \alpha \cdot L_0 \cdot \Delta T
$$
Where:
ΔL = Length variation (mm)
α = Thermal expansion coefficient
L₀ = Original length (mm)
ΔT = Temperature change (°C)
For the engine cylinder block main bore (L₀=26mm, ΔT=110°C):
$$
\Delta L_{block} = 23 \times 10^{-6} \times 26 \times 110 = 0.066\ \text{mm}
$$
For the steel plug (ΔT=40°C):
$$
\Delta L_{plug} = 12 \times 10^{-6} \times 26 \times 40 = 0.012\ \text{mm}
$$
Resulting in a thermal gap of:
$$
\text{Gap} = 0.066 – 0.012 = 0.054\ \text{mm}
$$
Material Compatibility Analysis
| Parameter | Original Sealant | Optimized Sealant |
|---|---|---|
| Elongation at Break | 64% | 186% |
| Shear Strength | 1.6 N/mm² | 7.0 N/mm² |
| Breakaway Torque | 21 N·m | 40 N·m |
| Thermal Gap Tolerance | 0.032mm | 0.082mm |
Sealant Performance Verification
The modified sealing solution demonstrates superior performance in engine cylinder block applications:
$$
\tau_{\text{max}} = \frac{F_{\text{shear}}}{A_{\text{contact}}}
$$
Where:
τmax = Maximum shear stress
Fshear = Axial load from oil pressure (220N)
Acontact = Effective sealing area (38.5mm²)
For original sealant:
$$
\tau_{\text{original}} = \frac{220}{38.5} = 5.71\ \text{N/mm²} > 1.6\ \text{N/mm²}
$$
For optimized sealant:
$$
\tau_{\text{optimized}} = \frac{220}{38.5} = 5.71\ \text{N/mm²} < 7.0\ \text{N/mm²}
$$
Durability Test Results
| Test Parameter | Original Sealant | Optimized Sealant |
|---|---|---|
| Initial Torque | 60 N·m | 60 N·m |
| Residual Torque | 50.5 N·m | 125.9 N·m |
| Thermal Cycles | Failed at 8h | Passed 800h |
| Seepage Occurrence | 100% | 0% |
Conclusion
The engine cylinder block oil leakage mechanism was successfully addressed through:
- Thermal expansion compensation through high-elongation sealant
- Improved anti-loosening performance (125.9 N·m residual torque)
- Enhanced shear resistance (7.0 N/mm² vs 1.6 N/mm²)
The optimized solution demonstrates reliable sealing performance in engine cylinder block main oil passage applications under extreme thermal and mechanical loading conditions.