Thanks to Hugh Ashburn for asking this question on our Facebook page.
I assume when you say “older,” you mean a classic car or hot rod with a flat-tappet camshaft.
Compared to their roller-cam counterparts, flat-tappet cams undergo sliding contact rather than rolling contact. This results in increased friction and, potentially, wear.
Added wear can affect valve lift and duration, which reduces engine power and efficiency. In extreme cases, increased pressure can remove material from the lobes and deposit it in the oil, where it circulates through the engine and causes damage.
Break-in helps harden the metal so it’s more resilient to wear.High zinc motor oil Engine builders and gearheads typically use high-zinc and high-phosphorus (ZDDP) motor oil to offer extra protection for flat-tappet cams, lifters and other components during break-in. AMSOIL Break-In Oil, for example, contains 2,200 ppm zinc and 2,000 ppm phosphorus.ZDDP anti-wear additives are heat-activated, meaning they provide wear protection in areas of increased friction. In this case, it’s at the cam lobe/tappet interface. The additives form a sacrificial layer on part surfaces, which absorbs contact and helps prevent cam and tappet wear.
That way, your engine makes maximum power and lasts as designed.Take a seat Even though Hugh didn’t ask about it specifically, I should also mention the importance of seating the piston rings during break-in.
Although a new or freshly honed cylinder appears smooth to the naked eye, it actually contains microscopic peaks and valleys. If the valleys are too deep, they collect excess oil, which burns during combustion and leads to oil consumption.The sharp peaks, meanwhile, provide insufficient area to allow the rings to seat tightly. That means highly pressurized combustion gases can blow past the rings and into the crankcase, reducing horsepower and contaminating the oil.
Breaking in the engine wears the cylinder-wall asperities, providing increased surface area for the rings to seat tightly. The result is maximum compression (i.e. power) and minimum oil consumption.Engine cylinders and piston rings during break-in.
Kevin Carey
Certified AMSOIL Dealer
(Content from Amsoil Technical Services)