A camshaft lobe sees some of the most brutal contact stresses in your engine. At the moment the lifter transitions from the base circle onto the opening ramp, the contact patch between a flat tappet and cam lobe is roughly 0.020" wide by 0.5" long — that's about 0.01 square inches carrying the full valve spring load. With 350 lb of spring pressure over the nose, that's 35,000 psi of Hertzian contact stress, cycled thousands of times per minute.

To survive this, cam lobes get surface-hardened. There are three common processes:

• Chill-cast iron — the traditional method for factory cams. Molten iron is poured against a chilled mold at the lobe location, producing a hard white-iron surface (Rockwell C 50-55) over a softer gray-iron core. Cheap, effective, but the hardened layer is only 0.030-0.050" deep.
• Parkerizing (manganese phosphate) — not actually a hardening process, but a conversion coating that provides an oil-retentive surface for the critical first 20-30 minutes of break-in. That dark gray finish on a new flat-tappet cam? That's Parkerizing, and it's why you never wipe it off with brake cleaner before install.
• Nitriding — the modern high-performance solution. The cam is heated to 950°F in an ammonia atmosphere, diffusing nitrogen into the steel surface to form iron nitrides. Produces a case 0.010-0.020" deep at Rockwell C 65-70, with excellent fatigue resistance.

The flat-tappet wipe crisis: Around 2004, the EPA-mandated reduction of ZDDP (zinc dialkyldithiophosphate) in motor oil from ~1,600 ppm down to ~800 ppm devastated flat-tappet cam survival rates. ZDDP forms a sacrificial phosphate glass under extreme pressure — exactly the sliding contact you get between a flat tappet and cam lobe. Roller cams don't need it (they roll instead of slide), so oil companies optimized for modern engines and killed the vintage rebuild market.

Break-in rule of thumb: Fire a fresh flat-tappet cam and immediately run it at 2,000-2,500 RPM for 20 minutes. Never let it idle. This ensures enough oil splash from the crank to reach the lobes, and keeps lifter rotation active so the break-in wear pattern spreads evenly. Use a break-in oil with 2,000+ ppm ZDDP (Comp Cams, Driven BR30, or equivalent).

Real-world example: A common failure mode on 1960s-70s American V8 rebuilds is losing a cam lobe within 500 miles because the builder used modern SN-spec 5W-30. The lifter face wipes flat, then galls the lobe, and metal contaminates the entire oil system.