In auto racing, small details have a major impact on success—a concept very familiar to performance racing parts provider Oliver Racing Parts (Charlevoix, MI). Oliver produces performance connecting rods for the world’s leading engine builders. These engines have powered champion race teams from NASCAR to the NHRA. Oliver Racing has built a reputation for producing some of the best connecting rods available. The company uses the SH-4000 honing system from Sunnen Products Co. (St. Louis) to meet the extreme tolerances on connecting rods that power the championship race team.
To produce the connecting rods, the company uses the Sunnen SH-4000 honing system in the final step of Geometric Dimensioning and Tolerancing (GD&T), a process control method. The GD&T technique enables Oliver to reach high degrees of circularity, parallelism, and perpendicularity.
“Connecting rods are critical to the performance of a racing engine, and honing is the most critical process in how we make our connecting rods,” said Joe Moch, president and CEO of Oliver Racing Parts. “The SH-4000 gives us the ability to reach high degrees of bore circularity-roundness, parallelism of the pin bore to the crank bore, and crank bore-to-face perpendicularity. These are the major factors that govern the relationship and performance of connecting rod crank and pin bores,” he explained.
According to Oliver, a typical V8 racing engine running at 10,000 rpm requires the rotating assembly to spin at over 166 times per second, with virtually all of the force getting transferred through the connecting rod. Each revolution requires that the piston and connecting rod go through a full compression cycle and a full tension cycle. Under these extreme conditions, connecting rods with wider tolerance margins are at risk of causing oscillations and stress concentrations in the rotating assembly, which then compromise friction of the reciprocating assembly.
GD&T ensures consistency by using the same three datum points throughout the manufacturing process. This triangulation method considers the six degrees of freedom along a 3D coordinate system using datum surfaces A, B, and C. Surface A controls three degrees, surface B two degrees and surface C one. Oliver’s machinists and engineers can refer to a controlled feature on each part at any point during the manufacturing process and make any necessary adjustments. GD&T also maintains and controls the part’s weight, balance, and dimensional accuracy. This helps determine a strict standard for all individual products, as well as a built-in auditing system to maintain the standard from part to part.
“Achieving consistent, exact measurements between the pin bores and intangible axis surfaces is only possible through GD&T, and the results of using this method are measurable,” added Moch. “Our rods reduce frictional loss to the absolute minimum, directly improving engine durability, performance, and longevity. Most importantly, it allows the entire reciprocating assembly to be more efficient and ultimately generate more power.”
The SH-4000 is Sunnen’s next generation power-stroke honing machine. It uses patented digital-servo tool feed and cutting pressure control for consistent, predictable performance to achieve micron-level finish tolerances. The GD&T process controls the parallelism throughout manufacturing, leading up to the final honing operation. As a result, parts require less stock removal during honing, reducing the need for adjustments and ultimately leading to better tooling life throughout the honing process.
Oliver credits the new hone with meeting critical surface finish tolerances, as well as critical bore size control, roundness and straightness of the crank bore, and perpendicularity of the crank bore to the crank bore face. The shop runs its SH-4000 with Sunnen’s SRT connecting rod tooling and a proprietary honing fixture (AFX-1000) to ensure the relationships of the crank bore to the pin bore.
“We used an ML-5000 previously, and the SH 4000 has a lot of neat upgrades and ease-of-use improvements,” said Moch. “Direct spindle tooling contributes to part roundness and parallelism through accuracy and repeatability. The squareness of the faceplate to the honing tool and flatness of the face ring to faceplate have really reduced the tolerance window of our parts. The control is easy to operate and we can really dial in the crosshatch pattern, which increases part performance. And the race teams love that.”
Quality parts at Oliver start with US-made, certified 43440 aircraft quality (AQ) material, which is vacuum furnace degassed and inspected for cleanliness to the AMS2301 standard. This high-quality material improves part durability and fatigue resistance. The shop also uses a custom two-stage heat treatment process designed to “grow” the best grain structure possible—something critical for cyclic durability throughout heavy use.
After rods are fully machined, they go back out for heat treating. During this second heat-treat stage, the Rockwell hardness is increased to an optimal level of Rc 38–41. This process is specific to Oliver rods and tailored to get the highest performance from the material. The result is a connecting rod with higher ultimate tensile strength and yield strength.
Oliver also believes temperature control is a key component of its production accuracy. The company operates out of a new state-of-the-art climate-controlled facility that is maintained through four HVAC systems. These systems automatically preserve a targeted temperature range within 4°. This eliminates any expansion or contraction that may otherwise occur, and the positive pressure atmosphere keeps particles in the air to a minimum.
The shop’s CMM is located on the shop floor, so parts are measured in the same atmospheric and temperature conditions as they are machined. Temperature consistency is maintained throughout all measuring activities. In fact, once received into the facility, Oliver’s connecting rods are held within the same temperature window from raw material to finished product.
The SH-4000 is the final element in a long line of finely tuned processes that deliver high part quality. “It would be crazy to go through everything we do—the high-quality steel, the temperature control, GD&T—and then trust the finishing stage to an inferior hone,” said Joe Moch. “This is a great machine, and we’re glad to have it on the shop floor. The hone’s repeatability and ability to cut all kinds of materials quickly and efficiently helps us meet our very strict internal specs and continue our affiliations with the champions of racing.”