I. Pre‑operation Requirements
Confirm crack location and size: Repair is allowed for non‑penetrating cracks in non‑critical stress‑bearing areas (excluding combustion chambers, main bearing seats and bolt holes). Replace with original factory parts directly for penetrating cracks or those in critical areas.
Tool preparation: Grinder, welding machine (cold welding/TIG welding), special welding rods/repair compound, hydrostatic testing equipment, cleaning agent.
Safety protection: Wear protective face shield and gloves; clean the operation area; keep away from open flames and oil contamination.
II. Common Repair Processes (Practical Steps)
Process 1: Cold Welding for Cast Iron (Preferred for Cast‑Iron Cylinder Block/Cylinder Head)
Grinding: Cut V‑ or U‑groove along the crack; thoroughly remove oil, scale and rust to expose the base metal.
Preheating: Preheat at low temperature of 100‑150℃ to prevent crack propagation.
Welding: Use nickel‑based special welding rods for cast iron; adopt low‑current and short‑segment intermittent welding. Tap each welded segment to release stress.
Finishing: Grind the weld smooth after welding; conduct hydrostatic testing at 0.6‑0.8 MPa. Pass the test if no leakage occurs.
Process 2: TIG Welding for Aluminum Alloy (Exclusively for Aluminum Cylinder Heads)
Cleaning: Grind the crack and cut grooves; remove oxide layers and clean the surface.
Welding: Perform TIG repair welding with controlled current to avoid burning loss and blowholes.
Inspection: Grind smooth and carry out leakage test; proceed if no abnormalities are found.
Process 3: Emergency Adhesive Repair (For Low‑Pressure Non‑Critical Areas)
Grinding and degreasing: Roughen the area around the crack and completely remove oil contamination.
Application: Apply high‑temperature‑resistant (≥200℃) special cast‑iron repair compound evenly on the crack for reinforcement.
Curing: Allow curing as instructed by the repair compound. Prohibited for high‑temperature and high‑pressure areas.
Process 4: Bushing/Insert Reinforcement (For Cracks at Bolt Holes and Cylinder Bore)
Machining: Mill the cracked area flat and machine the bushing/insert to matching dimensions.
Fixation: Secure the bushing/insert to the cracked area via welding or interference fit.
Grinding: Refine the surface to ensure close fitting with the original part, then conduct leakage test.
III. Critical Prohibitions (Mandatory Reading)
Repair is strictly forbidden for cracks in combustion chambers, valve seats, main bearing seats and all penetrating cracks; replace with original factory parts directly.
Hydrostatic/leakage test must be performed after repair to eliminate hidden risks of water and oil leakage.
Cylinder head bolts shall be tightened following standard torque and sequence to avoid secondary stress cracking.
Ordinary electric welding is prohibited for aluminum cylinder heads; high‑temperature hot welding shall be avoided for cast‑iron cylinder blocks (prone to deformation).
IV. Precautions
All repair materials shall match the material of Volvo cylinders (cast iron/aluminum alloy).
Clean tools after operation, reset equipment, and record repaired positions and adopted processes.
