Engine Lubricants - Solving The Flat-Tappet Puzzle

Flat-tappet camshafts are commonplace in the motorsports scene. From NASCAR Sprint Cup Series to IMCA Mods, guys across the nation are running this venerable design. About ten years ago, these cams started failing for no apparent reason. Through quite a bit of hard work, the cam companies eventually got to the root of the problem...oil. Since then, it has been fairly well publicized and one would think with all the media coverage of the subject racers would have caught on. However, people are still experiencing problems with their flat-tappet cams so we decided to take a look at the solution.

Of course before delving into the solution, let's take a look at the problem. All motor oils contain a variety of additives based on their intended use-high RPM, high mileage, low temperature, etc. Some have more, some have less. It all depends on the application. For years, one of those additives was Zinc Dialkyl Dithio Phosphate, or more commonly known as ZDDP. Originally developed in the '30s, ZDDP is an anti-wear/anti-oxidant additive. It also offers up excellent anti-scuffing properties as well, making it a perfect protectant for engines running flat-tappet cams. It was a standard ingredient in motor oil all the way through the '90s.

Unfortunately, the phosphorous in ZDDP plays havoc with catalytic convertors. The roller cam engines of today's production cars don't require the oil to have a big shot of ZDDP, so Detroit lobbied the oil companies to drop the ZDDP levels to preserve the cats and, subsequently, make it easier to achieve the government mandated 100,000 mile emissions warranty.

The problem was nobody in the oil companies said anything to the aftermarket. "I think from our standpoint they neglect to see an entire market that exists today," says Comp Cams' Scooter Brothers. "They saw it only through their eyes and figured everything has roller cams in it so it's no big deal. Let's just do it."

These formulation changes had a huge effect on the aftermarket that rippled through the racing community, and Brothers had firsthand experience with it. "Many years ago I had the problem with the engines from Roush. We couldn't even get an engine off the dyno without failing a cam," says Brothers. "We kept beating ourselves up thinking we didn't know how to make a cam anymore. We changed tapers, we changed lifters, we changed everything we knew how to change on the cam looking for the solution."

Brothers sort of laughs about the incident now, but it was a lot of work back then.

"We went through all kinds of things throughout this process of trying to find out what was wrong, scribing a little line on the lifter bores to squirt a little oil down there, drilling a hole in the bottom of the lifter, putting a spray bar in there to spray oil directly on the cam. Well, that was when Roush was sponsored by Valvoline, and we found out that somebody in the Valvoline labs changed something in the oil. As it turned out, as long as we had the correct oil it was fine. You know we just didn't have the right lubricant package in the oil." Once Brothers and Roush got the manufacturer to put the ZDDP back in the oil, the problem went away.

In heavily loaded applications such as a race motor, an oil wedge between metal parts such as camshaft, rockers, etc., cannot be sustained. As a result, metal-to-metal contact will occur unless a sacrificial coating is formed (see chart A, p.48). ZDDP is a polar molecule, so it's attracted to carbon steel surfaces where it reacts with heat, to create that sacrificial coating. The protective coating prevents metal-to-metal contact, which reduces friction and wear, and ultimately in a race motor prevents flat-tappet cam failure.