Metal stitching, sometimes also called cold pinning, has been around for over 100 years. It is a very well established and proven technology. It is mostly used on cast (gray) iron components such as engine blocks and casings although the repair of other materials such as aluminium and bronze is possible too.

The advantages of metal stitching are many:

  • Usually, little or no dismantling is necessary. Proper access from one side is generally sufficient.
  • Since it is a cold-repair method, no additional stresses, which over time may lead to new cracks, are introduced into the material.
  • The original alignments of the parts can be retained. There is no deformation or blemish due to the application of heat. Re-machining after repair is therefore often not necessary.
  • The repair seam helps to distribute tensile stresses over a larger area
  • If done properly, then the repaired area is liquid and gas tight. QuantiServ has successfully applied water pressure up to 12 bars (174 psi) to a test piece that was repaired by metal stitching.
Metal Stitching 2

After determining the extent of cracking, lines of holes are drilled at right angles to the crack. The holes are then converted to slots by connecting the holes. Preformed locks are inserted in the slots forming a connection across the crack. Then holes are drilled along the crack line between each stitch. These holes are tapped for placing special screws to fill the crack. The stitched area is ground to conform to the base metal contour, thus completing the repair.

Cracked cylinder block before (left) and during metal stitching (right)
Cracked cylinder block before (left) and during metal stitching (right)

If the component undergoing repair is not only cracked but if a piece is missing, then we prefabricate a new piece and lock it in place in the same manner as described above.

Over the years QuantiServ’s metal stitching experts have repaired many engine blocks, casings and other castings.  We helped their owners and operators to save a lot of money and reduce the equipment down-time from the several months that it typically takes to produce, ship and install a new part to days or weeks at most. And since most of the metal stitching repairs on board ships were carried out during the voyage, any off-hire or other interference with the vessel schedule could usually be avoided.

Metal stitching of a small crack near the bottom of a 2-S engine A-frame in Singapore
Metal stitching of a small crack near the bottom of a 2-S engine A-frame in Singapore

Case Studies

Our metal stitching specialists recently repaired an extensive damage on a 12-cylinder, 40-bore engine block on a cruise ship. All work was carried out while the ship remained in service:

The damaged was caused by a connecting rod side-kick. Here shown is the damaged engine block after dressing up.
The damaged was caused by a connecting rod side-kick. Here shown is the damaged engine block after dressing up.
With the help of 3-D scanning a precisely fitting new section was cast. Here it is shown during stitching.
With the help of 3-D scanning a precisely fitting new section was cast. Here it is shown during stitching.
The newly manufactured section is now stitched in place. The next step is the installation of the locks.
The newly manufactured section is now stitched in place. The next step is the installation of the locks.
During the installation of the locks. Notice how big and therefore strong they are!
During the installation of the locks. Notice how big and therefore strong they are!
In-situ milling, drilling and tapping completes the repair.
In-situ milling, drilling and tapping completes the repair.
The repair is hardly visible and the block is at least as strong as it was before the incident.
The repair is hardly visible and the block is at least as strong as it was before the incident.

The following photos show the repair of a marine gearbox cover by metal stitching, carried out last year in Namibia:

Severely damaged gear box cover after dressing up of the fractures
Severely damaged gear box cover after dressing up of the fractures
Fixing a prefabricated new section in place by metal stitching
Fixing a prefabricated new section in place by metal stitching
The casing after completion of the repair, before painting
The casing after completion of the repair, before painting

Here is an example of a repair of a marine gearbox foot, carried out by QuantiServ’s experts in Russia recently:

Fractured marine gear box casing
Fractured marine gear box casing
Damaged area dressed up in preparation for repair by metal stitching
Damaged area dressed up in preparation for repair by metal stitching
Prefabricated repair piece prior to installation
Prefabricated repair piece prior to installation
Repair piece installed with one M10 bolt to hold it in place
Repair piece installed with one M10 bolt to hold it in place
Metal stitching of the repair piece to the gear box casing in progress
Metal stitching of the repair piece to the gear box casing in progress
The result, approved by the customer and classification society
The result, approved by the customer and classification society