An In-depth Look at Today's Motor Oil and Its Possible Effects on Flat-Tappet Camshafts
You may be aware that camshaft failure is a growing hobbyist concern. Lately, it seems we can always find someone discussing this at our local cruise-in or on Internet message boards. A common fallacy about camshaft failure is that "It won't happen to me." Most people rationalize this by combining name-brand engine oils and filters with shorter change intervals. That action, however, may have little effect.
Even with top-quality oil and routine changes, our Pontiac had developed a distinct exhaust "pop" under load. Since its cam and lifters were over 10 years old and had traveled several thousand issue-free miles in that time, we hoped to find something as simple as a rocker arm that needed readjusting. But once the valve covers and valley pan were removed, we found much worse--a severely worn camshaft lobe. With no real wear on subsequent lobes or lifters, it appeared we were victims of an oil-quality-related failure.
Every Pontiac engine from 1955 through 1981 had a flat-tappet camshaft like that shown here. And most on the road today still use hydraulic or solid flat-tappet grinds. Notice the normal polishing pattern that occurs after proper break-in. Ideally the components will maintain this appearance for several thousands of miles.
Oil is considered the lifeblood of an engine; it is designed to complete many tasks. Not only does it suspend the small contaminants that get trapped in the filter, it is also a frictional lubricant and surface coolant for such engine internals as the crank and camshaft, pistons and connecting rods, and rocker arms and valvesprings. But how much do we really know about the oil on the market today?
Current oils are not only designed to last longer, reduce oxidation and deposits, offer far better low-temperature performance, and increase fuel economy, they are also designed to reduce emissions. It is this last quality that may be affecting older engines. So follow along as we explore the current oil standard and its potential effects on the valvetrain.
Oil Basics
Like any other facet of our hobby, engine oil is constantly changing as new refinement techniques are developed. But as consumers we never realize how often. And with recent advances in synthetic technology, many hobbyists feel that conventional (or mineral) oil is an inferior product. But it, too, is vastly superior to what was available just a few years back.
For oil to meet current standards, it must comply with formulation regulations introduced in 2004. Since phosphorus can have a negative effect on catalytic converters, a limit has been placed on the maximum amount of a zinc-phosphorus, antiwear additive in oil. This applies to any synthetic or conventional oil currently on the market with the latest approval ratings.
Whether synthetic, conventional, or a blend of the two, engine oils can be broken down into two basic types--monograde and multigrade. Monograde oil (also called single-grade) provides a stable viscosity--or its ability to flow at a given temperature. And while monograde oil may have offered slightly better operational consistency in the past, it can be too thick for quick engine circulation during the initial start-up period in cold conditions.
Multigrade oils were developed to offer maximum engine protection in nearly any condition or climate. This concept entails incorporating specific chemical additives to a single-grade oil to produce a hybrid with varying viscosity that can react to temperature changes. The main benefit of multigrade oil is improved circulation as a lesser viscosity oil when cold, and improved protection as a heavier viscosity oil in normal conditions.
Advertised viscosity of a typical multigrade oil starts with the viscous rating of the base oil at 0 degrees F, which is then followed by a W (signifying "winter"), and the maximum viscous rating when warm. Simply stated, 10W-30 would protect like single-grade, 10-weight oil when cold, and single-grade, 30-weight oil in typical operating conditions.