INTRODUCTION/ Renovation for crack repair: LOCK-N-STITCH


  • Problems Of Repairing Cast Iron 


Because yield and tensile point of cast iron are the same, it cannot bend or stretch to absorb stress caused by thermal expansion and contraction. 
This is why cast iron must be preheated over 482 in order to relieve stress. 
At 649 cast iron can stretch to relieve stress under strict oven welding procedures. 
All welds properly performed on cast iron result in some distortion. This often requires re-machining of critical surfaces.
The high carbon content gives cast iron many of its desirable characteristics like free machinability, uniform heat transfer, excellent wear surface and high quality casting capability.
However, it is responsible for the lack of difference between yield and tensile strengths.
And hardening is caused by the weld or Heat Affected Zone cooling too fast. Rapid cooling of high carbon iron and steels will cause hardening. In cast iron, hardening results in brittleness and the loss of good properties such as vibration dampening and ductility.
Hardening will also make machining, drilling and tapping difficult if not impossible.


  • What Is Metal Stitching?


Metal Stitching is a technology to repair damaged or cracked metals using special designed pins and locks without welding. 
Special designed pins create a drawing force pulling the cracked parent metal contrary to the spreading force created by conventional thread.
Additionally, high tensile strength locks are used where additional structural strength is needed. 
By installing pins and locks, the repaired part can be stronger than original and perfect sealing is also guaranteed.
Special designed Full - Torque thread inserts can be used to repair a stripped or cracked bolt hole permanently.


  • About L Series Stitching Pins


The most important thing to remember about the L Series pins that when tightened into the casting they seal on the threads because the pin is bigger than the tapped hole. This results in spreading pressure on the crack. If the casting doesn't have enough structural strength to contain the spreading pressure, extension of the crack can occur. 
Remember, L Series pins create spreading pressure. Our L Series pins consist of three different diameters, several different thread length, and are made of either steel or aluminum. The steel pins are made of a soft machinable steel that has the same expansion rate as cast iron with about the same hardness and corrosion resistance. All LOCK-N-STITCH pins are designed to be installed up to the shoulder so the head can twist off while leaving a small amount above the surface to grind or machine off. Because these pins seal on the threads, it is possible to install them at steep angles to the surface.




  • About Series Stitchig Pins


CASTMASTER (C Series) stitching pins do not spread the crack. In fact they do the opposite. This pin with its incredible SpiralhookTM threads creates a drawing pressure that actually pulls the sides of a crack together and permanently locks them together. C Series pins exert PULLING pressure. The installation process requires that every drilled hole receive a recessed spotface to assure some of the shoulder of pin remains below the surface after grinding or machining. The spotfacing is accomplished with a special piloted tool. 






  • About Locks


LOCK-N-STITCH Locks are made of 4130 heat-treated steel plate for maintaining the tensile strength of 175,000 psi.
Locks are wire EDM cut for accuracy, in all cases our locks are much batter than Roll type or Punch type.



Locks are used to add strength across a crack. Special drill jig are used to create the precision pattern that locks are driven into. All of our locks have a unique ability to pull the sides of the cracks together. This is not done to close the crack but rather to prevent any spreading pressure from being applied to the repair site. Use locks whenever the utmost strength is required. Always use the largest locks possible. Locks can not be bent around corners or curves. They must be installed flat. Use CASTMASTER pins on curves and locks on flat surfaces. The use of locks and CASTMASTER pins will produce the strongest repair possible.



Lock can be installed to add strength across cracks.

Locks are intended to be stacked or laminated to a depth of 80% of the thickness of the material being repaired with a hammer.

Lock pattern holes are drilled with a special drill jigs and all of locks have a unique ability to pull the sides of the crack together.

 Using locks and CASTMASTER pins together will be stronger than original.





L Series Stitching Pins :


The L Series pins can be installed at any angle to the surface and are used to repair the following types of cracks:


1. In combustion chambers of cylinder heads,

2. To secure and seal a patch for a blowout hole in an engine block.

3. To plug and seal a pinhole.

4. To fill scratches, dents and other imperfections on machined surfaces.

5. Seal simple cracks less than 3 in length.

6. Many other cracks and joints where there is enough strength in the surrounding metal to contain the spreading force of the pins.


Series Stitching Pins:


The following are examples of repairs done with C Series stitching pins:


1. All cracks placed in tension across the repair.

2. All cracks that run parallel with an inside or outside corner.

3. All cracks that will be strained by tightening a bolt in close proximity to the repair.

4. Repairs where using Locks is prohibited by access and/or contour.


Full - Torque


The cracks are often developed in bolt holes due to stress concentration at the thread or frequent tightening and loosing. 
Cracked threaded to holes have always been difficult to repair because of the spreading force exerted when the bolt or threaded device is torqued. Standard thread repair inserts and coils are ineffective in these situations. They can even make the problem worse by removing material around the threaded hole. 
Threaded holes in cast iron, aluminum, bronze and soft steel, exhibit a high frequency of cracking and stripping. The radial outward spreading force common to all threaded fasteners is the main cause of these problems.

Repairing the threads only solves part of the problem. By installing Full - Torque thread repair inserts you will solve the problem that caused the crack in the first place. The Full - Torque thread repair insert absorbs the spreading pressure of the fastener and transforms that pressure into a radial drawing force. This reversal of forces totally changes the effect that the fastener has on the repaired metal. Solving the problem is critical to making permanent repairs. When completed hole will be stronger and more durable than new. 
Full - Torque thread repair inserts restore both the needed strength and new threads at the same time. The threads on the outside of our inserts are the same unique SpiralhookTM threads used by our patented C Series crack repair stitching pins. Torqueing the bolt, stud, pipe plug, or spark plug pulls up on the insert, increases the load on the Spiralhook threads and adds to the radial drawing force of the threads. 
One of the best things to remember about Full - Torque inserts is that they can be installed very close to the edge without weakening the parent metal. This is a very valuable improvement over old thread repair technologies that actually weaken the area by making a larger hole and installing an insert that exerts radial spreading force when the bolt is tightened.








Hristo Hristov- tel. +359 52684 212, GSM +359 888 212423

Valentin Duchevski - tel. +359 52 684 210, GSM +359 888 842 553

Nayden Nedyalkov-tel. +359 52684 213, GSM +359 885 888 181

Fax: +359 52  684 216 

E-mail:christov@hhbrothers.com , hhbrothers@gmail.com , duchevski@hhbrothers.com





LOCK-N-STITCH,Full - Torque & CASTMASTERare registered trademarks of Lock -N - Stitch Inc. USA




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