Metal Stitching and the Use of Keys & Locks in Crack Repair

Metal Stitching, also called Cold Metal Repair or Metal Locking, uses precision mechanical techniques to restore cracked or damaged cast iron, cast steel, and aluminum components without welding or heat. Instead of melting the metal like welding does, this method uses specially designed keys and stitching pins (locks) to pull the cracked metal together and permanently seal the fracture.

This process is trusted in industries like,

• Marine engines and crankcases
• Power plants and turbine casings
• Pump and compressor housings
• Heavy industrial machinery

Why Not Welding?

Welding large cast components often causes:

• Heat distortion
• Loss of strength due to metallurgical changes
• Crack expansion or new cracks
• Metal stitching avoids heat damage and preserves the original material strength.

How Keys & Locks Work in Metal Stitching

The core of Metal stitching involves installing metal keys (locks) and stitching pins into the crack

Step-by-Step Explanation:

Step 1: Drilling and Stop-Holing

• Small holes are drilled at both ends of the crack.
• This prevents the crack from spreading during the repair.

Step 2: Installing “Locks” (Metal Keys)

• A series of overlapping slots are machined along the length of the crack.
• Technicians insert precision-engineered metal locks (keys) into the slots

Purpose of Keys/Locks:

• They mechanically pull both sides of the crack tightly together.
• They distribute load and stress evenly across the repaired area.
• The locks exceed the strength of the original casting and restore structural integrity

Step 3: Installing Stitching Pins

• Holes are drilled perpendicular to the crack.
• Technicians screw stitching pins into the holes to fill and seal the crack,

Purpose of Stitching Pins:

• They hold the metal in compression.

• They make the repair pressure-tight, preventing leaks of oil, coolant, or gas.

Step 4: Surface Finishing

• The repaired area machined flush.
• After finishing, the repair hides the crack and restores the component to OEM tolerances.

Advantages of Using Keys & Locks in Metal Stitching:

Benefit	Result
No heat involved	No warping or distortion
Strong mechanical reinforcement	Strength equal to or greater than original
Pressure-tight sealing	Ideal for engine blocks, heads, casings
Minimal downtime	No dismantling required—repairs can be done on-site
Cost-effective	Saves 60–80% vs. replacement cost

Where This Method Is Used

Metal stitching with keys and locks is commonly used for:

• Cracked diesel engine blocks
• Turbine and pump casings
• Compressor housings
• Marine engine frames and bedplates
• Generator casings

Whether the crack is small or several feet long, the stitching process scales to the size and location of the damage.

Metal stitching using precision metal keys and stitching locks is a reliable, proven, and cost-effective cold repair technique. Unlike welding, it involves zero heat—meaning no distortion, no stress, and no change in material properties. This method restores the structural integrity of cracked cast components and saves industries from huge downtime, dismantling, and replacement costs.

And when it comes to execution, RA Power Solutions is one of the leading global experts in metal stitching and metal locking. With four decades of experience and thousands of successful repairs, we specialize in restoring engine blocks, turbine casings, cylinder liners, compressor housings, and other critical equipment right at the site — anywhere in the world.

For more information on metal stitching repair of engine block cracks, metal stitching crack repair, engine block crack repair, and Crack in Cylinder Liner, please email us at rajshahani@rapowersolutions.com or info@rapowersolutions.com, or call us at +91 9582647131 or +91 9810012383.

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