Tech Stuff

Crankshaft Rescue

Racing crankshafts aren’t expendable pieces

Words by Todd Silvey

Photos courtesy Ohio Crankshaft

Racing crankshafts are held to very exact tolerances. Right out of the box from the manufacturer, the machined surfaces on the typical racing crank is held to a .003-inch minimum tolerance. With the tremendous torsional load that they sustain in a racing application, those precision ground tolerances afford exceptional load-carrying surfaces. That allows for increased endurance for the crank and the bearing surfaces.


During the conversion of the radial movements from the piston and rod to the rotating action of the crankshaft, the stress inflicted on a crankshaft is unbelievable in the drag racing world. Despite the use of the highest quality materials and the intense machining tolerances in your engine components, high rpm, launches, torque converters, and clutches are beating on them during every pass. The abuse on your crankshaft is never-ending.


The most prevalent disaster in the bottom end of a racing engine is the failure of a rod or journal bearing. The thrust bearing area, commonly located on the rear journal of the block is another frequent failure. Even without bearing failure, the crankshaft itself can be subjected to damage.  Normal wear of the crankshaft surfaces can cause cracks or bending, or even cause it to go outside of tolerable dimensions.


All this doom and gloom should not cause you to just throw that damaged expensive crankshaft into the trash. Very feasible repair techniques have been developed to solve these issues. The easiest repair is to clean up the damage by simply regrinding the typical rod and main journal to a smaller diameter. Bearings are easily obtainable to counteract the decreased crank journal diameter after this “regrind.” However, beyond the typical .010/.010 cleanup, the strength of the crankshaft may be questionable.


A trustworthy crankshaft specialist, such as Ohio Crankshaft, has the machinery and the skilled employees to rescue your costly crankshafts so they can continue to be utilized rather than trashed. In addition to stocking over 1,200 crankshafts for motorsport and hot rod applications, Ohio Crankshaft also examines and refurbishes many crankshafts every year. They are well-respected for their products ranging from motorsports to massive cranks utilized in industrial and agricultural applications. They are also often called upon to save vintage crankshafts that can’t be replaced.


“When it comes to material and hardening processed used, racing crankshafts are reasonably straightforward,” Ohio Crankshaft owner Stan Ray says. “Additionally, we repair crankshafts of all kinds, from large air compressors, to 7½ feet long Allison aircraft engine cranks, to WWII aircraft. These repairs can get tricky due to the unique materials and hardening processes needed. We have worked hard to master many welding and heat-treating processes through the years for multiple crank materials.”

Ray Darner heads the Ohio Crankshaft team that grinds new racing cranks, but also repairs over 500 cranks per year for customers. A prime example of a cost-effective crank repair is this damaged main and rod bearing journal. The bearing material you see embedded in the crank will be machined away prior to welding.


The first step Ray recommends in the process of repairing a crank is analyzing the damaged component.


“We want to talk to the customer first before they spend money to ship the crankshaft to us,” Ray explains. “We want them to describe in detail what type of crank it is, as well as an idea of the general damage it has sustained. We are successful in repairing some fairly serious damage, but if it’s not repairable, we want to save them the effort and money to ship it to us. We discuss what type of crankshaft they have and the damage description. We can usually determine if it is repairable before they ship, especially with the use of digital photos and a quick email. That helps us diagnose in many cases before we even have the parts in our hands.”


Once the crank is received, it is magnafluxed. This is a thorough inspection process done through magnetic particle testing. A ring of electrical current produces a magnetic field around the crankshaft. Then, a liquid solution which contains fine iron powder is flowed over the crankshaft. Any cracks in the metal will disrupt the magnetic field at that point, which concentrates the liquid/metal mix at the crack. An ultraviolet black light is then used to illuminate clearly any cracks which are usually invisible to the naked eye.

Magnetic particle testing, popularly known as the ‘Magnafluxing,’ happens when a ring of electrical current produces a magnetic field around the crankshaft. A metallic liquid solution soaks the crankshaft while an electric field and ultraviolet black light make cracks visible that can’t be seen by the naked eye (arrow).


Ray Darner has more than 30 years of experience in crankshaft grinding and repair at Ohio Crankshaft. He took us through their process of repairing crankshafts.


“The entire repair process requires us to determine which method works best for each crank we repair,” Darner says. “Every repair will necessitate different welding wire, welding heat, and welding speed.”


Before welding begins, the surfaces of the crankshaft are ground lightly to remove any foreign materials that may be embedded in the crank, such as bearing material. Crank journals may also be out of round at the blemished areas, so this also provides an even journal for welding.

This crank is carefully fixtured for welding. The welder torch is carefully programmed to follow the stroke and journal size of a rod journal while the crank is rotated at an exact rpm.

The submerged arc welding process uses a granular flux that flows over the active weld. The granular flux not only creates a shielding gas to keep impurities from the air out of the weld arc, it creates a slag of molten flux surrounding the weld as it cools. it also prevents weld splatter from damaging other areas on the crankshaft.


For the welding process, Ohio Crankshaft utilizes “Submerged Arc” machinery. This is considered to be the most productive method to get proper penetration of material build-up for re-machining. This welding operation allows gravity-fed flux to thoroughly cover the point of the arc from a high-amperage MIG welder. Just as any other welding process, a flux creates a gas that protects the welding arc from impurities in the normal air we breathe.


The welder is set up comparable to the crankshaft grinder. If a rod journal that rotates outside of the crankshaft centerline needs welding, the welder is programmed to coincide with the rod-stroke to maintain an exact distance between the welder tip and the journal motion.


“We pay close attention to the straightness of the crank throughout the repair process,” Darner describes. “From the beginning and throughout the welding and regrinding steps, we make sure the crank remains dimensionally straight. We also pay very close attention to repairing of the radius at each side of a journal to the specs. This part of the repairing process is where experience pays off. Weld penetration can change between the journal face and the radiused ends. Knowing your various brands and material makeup of each crank pays off.”

The pre-heating and post-heating processes are different between brands and crank material with Ohio Crank’s multiple ovens. The completed weld shows the careful welding of both the bearing face and radiused corners. Note the heat colorization on the crank surrounding metal.

The straightening station is used many times during the repair process to make sure welding and machining are not altering the crankshaft. Staff experience keeps everything to dimension without over-correcting during the hydraulic straightening operation. A repaired crank is then machined and re-ground in the same high-tech machinery used to create Ohio Crankshaft’s new product lines.


The straightening process is not quite high tech; the discerning process is more creativity than it is a science. The hydraulic crank press station is located strategically between the welding and grinding stations at Ohio Crankshaft’s facility. The station is comprised of fixtures along with multiple dial indicators that carefully audit multiple points along the length of the crank. Hydraulic pressure is then applied to bring the crank back to the correct tolerances.


“This is where experience pays off,” Darner notes. “We know how much counter-bending is needed to any given crank and expect it to return the proper tolerance. It's kinda like baking cookies; you just get experienced in what it takes between a 5140, 4340, or billet crank to bring it back to straight in one shot without going too far.


"Our experience goes into any heating of the crankshaft needed before and/or after the repair process," Ray says. "Depending on the crankshaft material and what kind of heat treating it had as a new product, we follow any pre- or post-oven time to hold the strength it had from its manufacturer."


Attention to detail is critical at the origin point between the welded surface and the grinder. It is essential that the process not be too assertive or add unnecessary heat into the welded area. Regrinding a crank is a little more deliberate than grinding a fresh one. But, crank welding and repairs are a completely practical option to get that damaged engine back on track quickly and less expensively.



Ohio Crankshaft




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