| Watts Shop Performance |
| Stock Forged Steel Rods |
| Original equipment forged steel rods are the next step up the strength and reliability ladder. Detroit sourced OE forged rods begin life as bars of carbon steel that are passed through a rolling die. The rolling process compacts the molecular structure and establishes a uniform, longitudinal grain flow. The bars are then heated to a plasticized state, inserted into a female die and pressed into the near final shape while a punch locates and knocks out the big end bore. In doing this, the grain flow at the big end is redirected in a circular pattern, like wood fibers surrounding a knot, and excellent compressive / tensile strength results. Finally the rod is put through a trimmer (that leaves the characteristic thick parting line on the beam), the big end is severed and machined to create the cap, bolt surfaces are spot faced, then final machining and sizing take place. But there are some drawbacks. When the forging hammer hits the hot bar, heat transfers from the bar to the hammer causing a phenomenon called de-carb (decarburization). Here, trace amounts of the carbon in the steel migrate to the surface resulting in a rough finish full of what metalurgists call "inclusions". An inclusion is described as anything that interrupts the surface of the metal or a lack of cleanliness (impurities) in the material. The effect of a surface inclusion can be likened to a nick in a coat hanger. Bend it enough times and the wire will fail, usually right at the nick. The rough surface caused by de-carb affect the surface to a depth of 0.005 to 0.030 inch and is packed with inclusion that are a breeding ground for cracks. The old hot rodder's trick of grinding and polishing the beams is a valid solution to this problem, though far too labor intensive to ever be considered by Detroit. When it comes to inclusion caused by impurities, Detroit's need to control cost can result in purchases of bulk steel that may (or may not) contain contaminants such as silicon that are not detected during manufacture. Such impurities can interrupt the grain boundaries between the parent molecules and lead to a fracture minutes or years after th rod is first installed in an engine. It's a matter of luck and what kind of abuse the flawed rod is subjected to. With very few exceptions, weakest link in a stock forged rod is the fastener system. The rod bolt is usually the most marginal component. Simply upgrading from stock bolts to quality aftermarket replacements can improve durability by 50%. Just be sure to have the big end resized to restore concentricity any time the bolts are removed. Stock forged steel rods are an economical choice that should be able to handle one horsepower per cubic inch with quality fasteners and as much as twice the factory rated output if the beams are polished. |