PRI 2017: Erson Cams Talks About Off-Index Lobe Grinding

The lighter shade of color on this lobe surface shows the depth of area treated for hardness on the lobe.

Not too often do we show up at a trade show and get an education on a topic that has been around for decades. That’s what happened when we passed by the Erson Cams booth this year.

Customarily, camshafts are produced by casting or forging a blank of cast iron, steel or other metal which is then hardened by heating and quenching. After the blank camshaft has been formed, the lobes and bearing journals are rough and finish machined, and then the lobe surfaces are hardened. After hardening, the lobes are ground to provide the desired contour and surface finish of the cam surface on each lobe.

How the hardened surface area can be thinned by off-index grinding.

Jack McInnis, longtime Rod Authority friend and engine expert, gave us the lowdown on camshaft cores that are off-index ground, potentially thinning the hardened surface of the cam lobe. This usually occurs when racers or engine builders ask for advanced timing built into the camshaft’s lobes.

“Cam lobes with thinned hardness area won’t endure the stress of racing valvesprings at high engine RPM – especially stronger valvesprings that produce higher nose pressures,” said McInnis. Because of the hardness surface thinning phenomenon, Erson Cams uses a process they call “index-grinding” to ensure the cams they grind maintain a consistent margin of hard material around the lobe.

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About the author

Bobby Kimbrough

Bobby grew up in the heart of Illinois, becoming an avid dirt track race fan which has developed into a life long passion. Taking a break from the Midwest dirt tracks to fight evil doers in the world, he completed a full 21 year career in the Marine Corps.
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