A flat-tappet camshaft and lifters, with the solid metal points of contact between the cam
Too often, failed camshafts and valvetrain components in stock car racing engines are blamed on the manufacturer. After all, you'd logically think it had to be a poorly manufactured or designed component if it wasn't capable of making it through the first race, wouldn't you?
But the truth is that forces involved in modern stock car engine design have conspired against the venerable flat-tappet design, and if the cam and lifters aren't broken in correctly, they can fail before the oil even gets up to temperature.
A flat-tappet lifter's design is notable because the portion of the lifter (or tappet) that contacts the camshaft is relatively flat and solid. It is designed to slide up and down the cam lobe, hopefully with a thin film of oil separating the lifter from the cam. This design hasn't been used in over-the-road cars for decades and has been replaced by the roller lifter. The roller lifter uses a wheel that rolls up and over the cam lobe, significantly reducing friction.
Flat-tappet lifters are significantly cheaper than roller lifters designed for performance, and they were original equipment for years in V-8 engines, so they are still mandated in the rule books for many different racing series. But in order to increase engine performance, cam designers are being pushed to design cam lobe profiles with extremely quick valve opening and closing rates. These radical lobe designs are so steep that the edge of the lifter could possibly dig into the face of the lobe. The design also narrows the contact area between the lifter and cam lobe and increases the pressure between the lobe and lifter as well.
Also, as engine revolutions per minute increase, engine builders are forced to use increasingly stronger valvesprings. The extra force these stronger springs provide while trying to push the lifter down against the camshaft also increases the pressure at the point of contact between the two components and makes it easier for the oil to be pushed out of the way, facilitating metal-on-metal contact.
Quaker State's Q Racing line of synthetic oils is designed specifically to meet the requir
Besides radical camshaft lobe designs and stiffer springs, the third side of this trouble triangle for flat-tappet cams is that motor oils these days simply aren't designed for the needs of these types of valvetrains. Modern oil blends for over-the-road cars-even so-called "performance" oils-are rarely capable of providing the protection needed. In modern engines with roller lifters, sliding friction isn't much of a concern, and designers instead worry about the oil's ability to protect the bearings and last longer than the standard 3,000 miles.
"There are different types of friction inside an engine," explains Mark Ferner, Quaker State's team leader for research and development. "For instance, the journal bearings. As long as there is a good film of oil between the shaft and the bearing, the shaft should ride on the film of oil and never contact the bearing while the engine is running. So all the engine really sees is the viscosity of the oil.
"But where the lifter and the follower are is a different story. Even in a passenger car engine, you've got high spring pressures and a relatively small point of contact between the rounded part of the cam lobe and the flat part of the follower. If you do the math, even for everyday passenger engines, you would see pressures about 200,000 psi. That's enough to squeeze the oil out of the way, no matter if it is a synthetic or conventional blend.
Quaker State's Team Leader for R&D, Mark Ferner. Photo by Quaker State
"For years, everybody [manufacturing motor oils] used a particular type of antiwear additive that everybody refers to as 'zinc' [to protect flat-tappet cams and lifters]. It's actually a longer chemical name, and there are different variations of the molecules, but it was all basically the same. [The other elements] in there are sulfur and phosphorus, typically. Those two additives react with the camshaft's iron surface and create a sacrificial chemical coating that is strong enough to keep the parts separated."
But engine manufacturers have switched over from flat-tappet to roller followers, and with roller followers there isn't that much friction. Ferner explains that oil manufacturers began pulling back on the zinc additives included in their blends because they weren't necessary, and the zinc in the oil that is vaporized and blown out the exhaust ports can reduce the efficiency of the O2 sensors and the catalytic converter.
As racers, we have no concern for O2 sensors or catalytic converters because they aren't even on our race cars. But we are a very small market compared to the passenger car market. In fact, new API SM standards that govern what goes into motor oil require manufacturers to use even less zinc than ever before. There are no ingredient lists on quart bottles of oil like you will find on food, so it sometimes can be difficult to know exactly what you are buying. But Ferner points out that if the oil you are considering has a label saying it is API SM compliant, you can be sure it has minimal protective attributes for a flat-tappet cam. One over-the-counter oil that has some of the attributes we are looking for is Pennzoil GP Performance Racing oil, which Ferner says has added antiwear additives for highly loaded valvetrains.
Here's an example of a cam that was ruined by improper or rushed break-in procedures. You
Competition Cams has done a lot of research on the effect different oils have on its products, and one solution the company found may surprise you. According to Comp, "Because of the more severe loads in diesel applications, many of the better diesel-use motor oils have high-pressure friction inhibitors as good or better than any of the previous automotive oils. The current API ratings to look for are CI-4 Plus, CI-4, and CF-4. Oils that meet these standards should be recommended at least through the flat-tappet break-in period along with Comp Cams' Pro Cam Lube applied to the cam and lifter and Comp Cams' Camshaft Break-In Lube oil additive."
Some of the diesel oils that meet these standards are: Castrol Tection Extra SAE 15W-40, Chevron Delo 400 Multigrade SAE 15W-40, Mobil Delvac 1300 Super 15W-40, and Shell Rotella T Multigrade SAE 15W-40.
Diesel-formulated oils (in addition to Comp's break-in lube additive) are good for breaking in cams and will even work for regular use if necessary, but they may not be the best option. "In a diesel engine, extra soot can get into the oil," Ferner explains. "In diesel oil, you typically will have more detergent to keep the oil clean and also a dispersant to keep the debris or soot in the oil from settling together in the low spots in the engine and forming bigger pieces. It keeps the debris circulating through the engine where, hopefully, it can by picked up in the oil filter. These additives aren't harmful to a race engine, but it can make the oil thicker than necessary in some areas. And if you are trying to find every bit of available horsepower, you want your oil to be as thin as possible and still protect your engine."