CAMSHAFT BEARINGS
Camshaft bearings are similar to crankshaft bearings, but camshaft bearings do not feature replacement shells, meaning — in a conventional engine — a new cylinder head is often required if the camshaft bearings have suffered excessive wear through the continued use of contaminated oil, or through oil starvation.
CAMSHAFT MATERIALS
Rockwell is a hardness scale based on indentation hardness of a material. There are different scales, denoted by a single letter to highlight different loads and indenter types. When testing metal, indentation hardness correlates linearly with tensile strength. The higher the number on the Rockwell scale, the harder the metal. Camshafts can be made from various materials, where Rockwell scaling is observed to ensure each part is fit for the intended application.
1. Hardenable Iron
This is Grade 17 cast iron with an addition of one percent chrome to create between five and seven percent free carbide. After casting, the material is flame or induction hardened, producing Rockwell hardness of 52 to 56 on the C scale. This material was developed in 1930s America as a low-cost replacement for steel camshafts.
It’s mainly suited to applications where there’s an excess of oil e.g. camshafts running in an engine block and splash-fed from the sump. Consequently, most aftermarket camshaft manufacturers only use this material for performance camshafts if the camshaft is splash-fed by a sump.
2. Spheroidal graphic cast iron (SG iron)
A material giving similar characteristics to hardenable iron. Its failing as a camshaft material is hardness in its cast form, which tends to scuff bearings in adverse conditions. The material will heat treat to 52 to 58 Rockwell C. This material was used commonly by Fiat in the 1980s.
3. Chilled chrome cast iron
Chilled iron is Grade 17 cast iron with one percent chrome. When the camshaft is cast in the foundry, machined steel influencing the shape of the cam lobe are incorporated in the mould. When the iron is poured, it hardens off very quickly (known as chilling), causing the formation of a carbide matrix (this material will cut glass) on the cam lobe. Chilled chrome cast iron is exceedingly scuff-resistant and is the only material for producing high quality Ohc-specification performance camshafts.
4. Carbon steel: EN8/EN9
Used mainly in between 1930 and 1945 and currently used for induction hardened camshafts in conjunction with roller cam followers, due to the through-hardening characteristics of the material.
5. Alloy steels: EN351 AISI 8620 and EN34 etc.
Used by British Leyland in its A Series and B Series engine and best used when supported by a chilled cam follower.
6.Nitrading steel: EN40B
The best steel for camshafts. When nitrided, it gives a surface hardness and finish similar to chilled iron. Aftermarket manufacturers use this material when replacing chilled iron camshafts in competition engines. Interestingly, this material is used on several recent competing engines in Formula One.
Conclusion
In general, steel is a good camshaft material, but the type of steel has to be matched with the cam follower it runs against because different grades of steel have different scuff characteristics.
When purchasing camshafts, enquire which material the parts are produced from. This will help you find a fit for purpose solution for your engine build. For example, a chilled iron camshaft may be more expensive, but its resistance to wear in all conditions far exceeds any other type of cast iron. Of course, all of the above is a simplified explanation of what camshaft materials are and their comparable pros and cons, but we hope the information here will help you to ask the correct questions when purchasing performance camshafts on the aftermarket.