How TIEGU, a Leading Foundry, Repairs Crankshafts with Minimal Damage

As a leading foundry specializing in high-quality crankshaft production, TIEGU understands that crankshafts may sustain minor damage during operation. This guide outlines our professional repair methods to restore crankshaft performance while preserving their integrity, ensuring extended service life and optimal functionality.

1. Initial Inspection & Diagnosis

The first critical step in repairing a slightly damaged crankshaft is a comprehensive inspection to assess its condition and identify issues accurately.

Visual Inspection for Surface Defects

Technicians start with a visual examination to detect visible flaws such as cracks, scoring, discoloration, or overheating marks. These clues pinpoint areas requiring further detailed analysis.

Non-Destructive Testing (NDT) for Hidden Damage

Advanced NDT techniques uncover internal defects invisible to the naked eye:

• Dye Penetrant Inspection: A special dye seeps into surface cracks, making them visible after developer application, ideal for surface-breaking defects.

• Magnetic Particle Inspection: The crankshaft is magnetized, and magnetic powder highlights surface/subsurface fractures by accumulating along crack lines.

• Ultrasonic Testing: Uses sound waves to detect deep-seated issues like internal cracks or voids, providing detailed subsurface insights.

Thorough Cleaning

Before inspection, the crankshaft is cleaned to remove contaminants (dirt, oil, grime) using ultrasonic cleaning for stubborn debris and chemical degreasing for heavy oil buildup. A clean surface ensures accurate defect detection.

Precision Dimensional Measurement

High-precision tools measure journal diameters, bearing clearances, and web thicknesses against OEM specifications to evaluate wear:

• Main Journal Diameter: Measured at the center with a micrometer to ensure compliance with engine requirements.

• Rod Journal Diameter: Multiple measurements check for taper/ovality, ensuring values stay within allowable tolerances.

• Journal Runout Test: Using a dial indicator on V-blocks, maximum allowable runout is ≤0.002" for inline engines; V-type engines allow ≤0.002" near supports and ≤0.004" for middle journals.

• Thread & Oil Hole Inspection: Threaded holes are cleaned with a chaser tap (no material removal), and oil feed holes for main/rod journals are cleared of debris, ensuring smooth oil flow without sharp edges.

2. Engine Dismantling Process

To access the crankshaft, follow a controlled dismantling procedure to avoid secondary damage:

Secure the Engine

Mount the engine on a stable workbench to prevent movement during disassembly, ensuring safety and precision.

Tool & Safety Prep

Gather specialized tools (bearing pullers, hydraulic pumps) and PPE, maintaining a clean workspace to avoid component contamination.

Step-by-Step Disassembly

• Remove front housing and flywheel housing to expose internal components.

• Carefully disassemble cylinder heads, pistons, and connecting rods; label and store parts to ensure correct reassembly.

• Remove main bearing caps, marking their orientation to maintain installation accuracy.

Key Equipment Requirements

• Lifting Device: Safely hoist the ~159 kg (350 lb) crankshaft using a rated lifting tool to prevent block collision.

• Specialized Tooling: Use bearing pullers and step plates for damage-free component removal.

• Contaminant Control: Collect fluids in approved containers and dispose of them per local regulations to avoid environmental hazards.

3. Targeted Repair Techniques

Repair methods are selected based on damage type and severity:

Crankshaft Grinding & Polishing

For surface wear, cracks, or deformation, restore geometry and surface finish:

• Grinding: Use a dedicated machine to grind journals against engine rotation direction, removing damaged material and correcting ovality/taper.

• Polishing: Polish in the engine’s rotation direction with abrasive belts/microfinishing tape to achieve a smooth surface (≤15 microinches Ra for standard crankshafts, ≤10 microinches Ra for high-performance models).

• Considerations: Avoid over-polishing ductile iron crankshafts to prevent "halo effect" on oil holes; ensure forged steel journals are polished in the operational rotation direction for consistency.

Straightening Bent Crankshafts

• Hydraulic Straightening: Apply controlled pressure (with localized heating if needed) using a hydraulic press to correct misalignment, aiming for total indicator runout (TIR) <0.0010" on critical surfaces.

• Peen Straightening: For minor stress-induced bends, strike journal surfaces with a peening hammer to relieve internal stress and restore straightness, ideal for preserving material integrity in precision applications (e.g., vintage/high-performance engines).

Crack Welding & Journal Restoration

• Welding: Employ modern techniques like submerged arc welding; use bronze/Eutaloy for small defects and ER70-S2 filler for cast steel crankshaft fractures.

• Post-Weld Treatment: Conduct stress-relief annealing/cryogenic treatment to eliminate internal stresses; grind welds and journals to OEM dimensions (tolerance: ±0.003").

• Quality Check: Perform wet fluorescent magnetic particle inspection to verify crack-free repairs, especially around journal fillets.

Heat Treatment for Hardness Adjustment

For localized hardening due to overheating, conduct controlled annealing (700–800°C for 1–2 hours) to reduce Brinell hardness by ~200 HB, restoring ductility and preventing brittle failure.

4. Post-Repair Quality Control

Surface Finish Precision

Achieve a mirror-like surface via superfinishing (oscillating silicon carbide stones) to minimize bearing friction and enhance long-term reliability.

Straightness & Fillet Restoration

Verify straightness on narrow V-blocks and restore journal fillet radii to design specs, critical for stress concentration reduction.

Cost-Effectiveness

Single-journal repair costs ~$600, with full rod journal repairs doubling the cost. TIEGU’s team optimizes solutions based on material (cast steel/ductile iron) and damage severity, balancing performance and economy.

5. TIEGU’s Professional Commitment

As an experienced foundry, TIEGU ensures every repair meets international standards using advanced equipment (high-precision grinders, hydraulic straighteners) and decades of expertise:

• Accurate Detection: Combine visual, NDT, and dimensional analysis to identify defects as small as millimeters.

• Customized Processes: Tailor grinding, welding, or heat treatment to the crankshaft’s material and structure.

• Traceability: Maintain full repair records and provide detailed reports for performance accountability.

By leveraging scientific repair methods, slightly damaged crankshafts can be restored to high performance without replacement, saving costs and reducing downtime. TIEGU’s technical excellence empowers core engine components, supporting efficient operations in industrial and transportation sectors.

For more information on crankshaft repair or custom foundry services, visit our website or contact our technical team.