Cam cores come in a variety of materials, and each has its own set of pros and cons during the grinding process. Cast-iron cores are typically used on flat tappet cams and are very easy to grind. SAE 5160 steel is used on roller cams and features a deep heat treat, but it’s easy to burn up if it’s too hard. Similarly, SAE 8620 steel is also used on roller cams, but has a shallow heat treat. It can be prone to burning up as well. Another option is SAE 5150 steel. It works great for street roller cams, but isn’t hard enough to use in some severe-duty race applications. In NHRA Top Fuel, SAE 9310 steel is used for its durability, but its toughness comes at a price. It’s slow to grind except when using CBN grinding wheels. This means that it’s not cost effective for most applications. PM M4 tool steel is another extremely durable material, but it’s almost impossible to grind accurately unless using CBN grinding wheels. As you can see, going to the Okuma grinders with CBN grinding wheels has opened up material options than were not previously available with conventional wheels. The Okuma machines have also reduced or eliminated the biggest issue with materials like 5160 and 8620 steel that are commonly used for roller cams.
Radical cam lobe profiles can really push the limits of cam grinding equipment. Fortunately, our new Okuma machines address several of these issues. For instance, the negative radius of curvature on the cam is supposed to be held at greater than twice the grinding wheel radius. This allows coolant to properly get between the wheel-to-cam interface during grinding. In the aftermarket, that rule is typically stretched a bit, but both burn and push off become much worse as you push the limits. Going to a smaller conventional wheel causes issues with very rapid wheel wear. That’s why a Berco grinder typically utilizes a grinding wheel starting at 18 inches and can get as small as 15 inches, if needed. On the other hand, the Okuma machines have a CBN wheel that starts about 350 mm and has a grinding layer that’s only 3 to 5mm thick. This allows the grinders to start at under 14 inches for more aggressive profiles. Likewise, the wheels stay in a very tight size range for improved accuracy and repeatability. CHP