An epidemic of cam failures has plagued owners of older cars recently. That part of the story is well established. The controversial part concerns the causes for the rash of prematurely worn camshaft lobes. This article will examine three conditions, each of which separately may put cam life in jeopardy, but in combination can make the "perfect storm" to sink your engine. If a flat-tappet cam resides in your car, the information presented here may help prevent expensive engine work. If it's already too late, as was the case for this writer and many thousands of others, this article will show how to recover from a wiped cam. New parts options and other related work will also be featured.
The beginning of problems for flat-tappet cams was the rise in popularity of roller cams. Over the past 20 years, nearly all engines have switched to roller lifters, as did Corvette in 1987. The positive effects of this included greater efficiency, more horsepower per cubic inch, and less friction. The negative effect is that flat-tappet engines decreased in importance to oil manufacturers and decreased in numbers produced. Three results of this that concern us are changes in specific antiwear additives in motor oil, the increase in popularity of synthetic oils, and the decrease in U.S. suppliers of flat-tappet lifters.
Oils Have Changed
Major brand name oils have changed recently. The levels of specific antiwear additives, such as ZDDP, that are critical to flat-tappets have significantly decreased. Yet nowhere is this mentioned on the label. A reason for the reduction is to ensure catalytic converters last longer. Eventually, trace amounts of these additives will get past the rings or valveguide seals and go into the exhaust. Most auto manufacturers, now required to warranty emissions control systems for 120,000 miles, specify the newly formulated oils. These oils carry the API "starburst" graphic, which looks somewhat like a gear. If you have an older engine, you may want to avoid oils that display the gear's "teeth" or your cam may get chewed up.
Flat-tappets have one of the most highly stressed and poorly lubricated surfaces in an engine. The hardened cam shaft lobe is dragged across the hardened lifter face under great pressures from valvesprings and valvetrain inertia. Think of dragging a motorcycle on its side over a speed bump. It's a high-pressure, high-shear wear point, and it is not directly lubricated. Lubrication comes from drops of oil thrown off the crankshaft to, hopefully, splash on the bottom of the cam lobes. And this lubrication is minimal until engine rpm increases. That's why it's recommended to break in new flat-tappet cams at 2,000 rpm or more.
The higher levels of specific antiwear additives, such as ZDDP, help protect this highly stressed wear point. However, most of the engines produced during the last two decades don't have this critical wear point because they have roller lifters. Think of rolling a motorcycle on its tires over a speed bump-much less wear than dragging it over. Some oil manufacturers will say that the reduced levels of antiwear additives are fine for flat-tappet engines, and they may cite one dimensional laboratory studies on the new oils. However, the real-world experience is that thousands of flat-tappet camshafts have failed prematurely.
There are two ways a person can ensure they are using oil that has sufficient amounts of antiwear additives, commonly listed as 1,200 ppm ZDDP for flat-tappet engines with stock valve springs and 1,400 ppm for engines with higher spring rates. The first is to buy oil that is similar to older formulations. This used to be as simple as buying a diesel-rated oil, such as Shell Rotella T and Chevron Delo 400. Diesel engines also have highly stressed wear points, but diesel oils were reformulated to CJ-4 in 2007. Although the levels of ZDDP were reduced, most are still significantly higher than common car motor oils.