Pins will not hold unless there is enough metal to grip and support the threads.įurnace welding uses a torch, an oven and lots of heat.Ĭracks in cast iron can be repaired by hot welding (furnace welding), but it is a technique that takes skill and lots of practice. This type of pin can actually hold a crack together rather than just fill it, and may be used to repair cracks that cannot be fixed with ordinary tapered or straight pins.Īnother crack that is difficult to repair by pinning is any crack that occurs in very thin (less than 1/8 inch wall thickness) area of a casting. "Castmaster" pins (manufactured by Lock-N-Stitch) have a unique "spiral hook" or "reverse pitch" thread pattern that grips both sides of a crack when the top shoulder of the pin bottoms against the metal. For these types of crack repairs, locking devices and/or pins with a self-gripping ability can provide the required reinforcement and strength. The same goes for cracks in an area of a casting that would open up or pull apart when the casting is under load or gets hot. Ordinary tapered and straight pins cannot handle certain kinds of cracks, such as those along an outside edge or corner that require support to hold the sides of the crack together. Various types and sizes of crack repair pins and plugs. This type of straight pin can also eliminate the need for installing valve seat inserts in cast iron heads. This eliminates a thread line on the surface enabling the surface to be machined. Straight pins also have an interference fit over their entire length, and a tapered shoulder that crushes into the surface. Straight pins are designed to twist off when tightened, eliminating the need to cut or grind the heads off (as is necessary with tapered pins). Straight pins are faster to install because an ordinary tap and power drill can be used to install them. The holes for tapered pins must be carefully hand tapped and the pins hand tightened for a tight seal. Sealer really is not necessary, but is often used for added insurance. This occurs because the threads on both the tapered pin and hole have an interference fit. Tapered pins pull themselves into a crack as they are tightened to provide a tight seal along the entire length of the pin. Each type has its advantages and may work better in certain situations than the other. There are two basic types of pins: straight and tapered. Pinning is a relatively easy technique to learn and use, does not require much in the way of tools except a drill, guide fixture and tap, and uses no heat.Įssentially, pinning involves drilling holes in a crack, installing overlapping pins to fill the crack, then peening over the pins to seal and blend the surface. Pins can also be used to repair cracks in aluminum heads and blocks, too, although TIG welding is often the preferred repair method for aluminum. Pinning is the most commonly used technique for repairing cracks in cast iron head, blocks and manifolds because it is fast, reliable and cheap. Various types of pins can be used to repair cracks You can even change the shape of the combustion chamber or a port by adding metal. Welding, on the other hand, restores integrity and allows you to fill cracks and holes. Tapered pins with sealer work well on most applications. A lot depends on the location of the crack and its severity. Pinning can repair about 80 percent of all cracks but it can't fix every kind of crack. That is why pinning has long been the most popular method of repairing small cracks in cast iron blocks and heads. But due to the high cost of many late model heads and blocks, crack repair may be a cost-effective alternative to buying a new or used casting to replace a cracked head or block.Ĭracks in aluminum heads and blocks are relatively easy to repair by TIG welding, but cast iron is much more difficult to weld. That is why most of the crack repair activity in the past was limited to high cost heavy-duty diesel heads, antique heads or other jobs that justified the time, effort and risk. But pinning has its limitations, and furnace welding is not something a novice can learn overnight.Ĭrack repair also involves a certain amount of risk. Pinning and furnace welding are both viable options that have long been used to repair cracks and other kinds of damage. There have always been options for repairing cracks in cast iron. So many engine rebuilders are now repairing heads they would have thrown out only a few years ago as unsalvageable. In Cast Iron Cylinder Heads and Engine Blocks Copyright Īdapted from an article written by Larry Carley for Engine Builder magazineĬrack repair has become one of today's hottest topics because good rebuildable cylinder heads for many late model engines are very expensive and hard to find. Repairing Cracks in Cast Iron Cylinder Heads and Engine BlocksĪuto Repair Library, Auto Parts, Accessories, Tools, Manuals & Books, Car BLOG, Links, Index
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