Cast-iron welding is not for your average backyard car crafter, but in the hands of a professional, you can save that precious numbers-matching block from life as a doorstop.Cast-iron welding is not for your average backyard car crafter, but in the hands of a prof Cracks. They are the bane of all car crafters, and cast-iron cracks are among the most difficult to repair. It’s really not even something you can do in your own shop unless you have years of experience and the right equipment. The variables of the type of cast iron (gray, alloy, nodular, malleable) and the various types of repairs are incredibly numerous and too complex to get into here. So this story is really about showing you some repairs and a couple of ways to go about them. When it came time to repair a crack in a numbers-matching 396 block for a Chevelle, the call went out to Kelly’s Block Welding in Los Angeles, where owner Garrick Preece and welder Jun Nakawatase applied their considerable experience to this repair. Check it out. Lock-N-Stitch Cast Iron Repair There is another process for repairing cast iron that does not involve welding. The Lock-N-Stitch company offers a repair alternative involving a series of interlocking, threaded pins inserted along the line of the crack. These pins actually pull in the damaged section of cast iron as they are tightened. They have been successfully used in both cast-iron and aluminum blocks and heads. If you can access the crack with a drill motor, this process can repair the crack without welding. To learn more about this process and the product, check out the company’s website, which contains several repair examples, including one Cummins Diesel engine that required removing a large section of the outside of the cylinder block and replacing it with a steel plate. It’s an amazing repair sequence. The arrows indicate the two cracks in this starter motor bolthole. The cracks occurred when an improper, non-knurled bolt was used to retain the starter. The bolt moved around under the torque loads imposed by a starter motor and cracked the block. The proper starter motor bolt includes a knurled section (arrow) that fits snugly in the counterbored mounting hole to secure the starter motor to the block.The cracks occurred when an improper, non-knurled bolt was used to retain the starter. The Next, Nakawatase used a wire brush on a drill motor to carefully clean the repair area to make welding easier.Next, Nakawatase used a wire brush on a drill motor to carefully clean the repair area to It’s also important that the starter bolt be the correct length, positioning half the knurling out of the bolthole to locate the starter motor housing to the block.It’s also important that the starter bolt be the correct length, positioning half the knur Nakawatase started the repair by using a die grinder equipped with a flame-shaped 3⁄8-inch carbide cutter to both grind down to the base of the crack and create a greater area around the repair for the weld.Nakawatase started the repair by using a die grinder equipped with a flame-shaped 3⁄8-inch To prevent the weld from penetrating into the threaded portion of the hole, Nakawatase used a carbon gouging rod cut with 3⁄8 NC threads. The rod is carbon so weld won’t stick to it, and that protects the existing block threads.To prevent the weld from penetrating into the threaded portion of the hole, Nakawatase use After he inserted the carbon gouging rod, Nakawatase also used a large Vise-Grip to clamp down on the cracks to minimize the opening and improve the repair.After he inserted the carbon gouging rod, Nakawatase also used a large Vise-Grip to clamp Kelly’s uses an old but nearly indestructible Lincoln AC arc welder to perform the repair. Right: He next applied localized heat to the repair area. This helps bring the temperature up to around 200 degrees F. Cast iron will quickly dissipate the heat.Kelly’s uses an old but nearly indestructible Lincoln AC arc welder to perform the repair. Kelly’s uses an old but nearly indestructible Lincoln AC arc welder to perform the repair. Right: He next applied localized heat to the repair area. This helps bring the temperature up to around 200 degrees F. Cast iron will quickly dissipate the heat.Kelly’s uses an old but nearly indestructible Lincoln AC arc welder to perform the repair. Kelly’s Block Welding uses a specific soft-nickel welding rod to perform the repair. This special welding rod is easily machined and is more malleable, which helps prevent cracking after the weld cools.Kelly’s Block Welding uses a specific soft-nickel welding rod to perform the repair. This This is the repair after the welding was complete. After some judicious grinding, Nakawatase ended up with a nicely repaired block that you have to look at very carefully to know it’s been repaired. A little Chevy Orange paint, and it is as good as new.After some judicious grinding, Nakawatase ended up with a nicely repaired block that you h SOURCES Kelly's Block Welding W. Los Angeles CA 310-306-6795 Lock-N-Stitch Inc. Turlock CA 800-736-8261 www.locknstitch.com By Jeff Smith Enjoyed this Post? 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