Flat-Tappet Cams and Worn Down Engines - The Perfect Storm
Flat-Tappet Owners Beware: Your Motor May Be Silently Grinding Itself Away
HOT ROD StaffWriter
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.
A high-energy magnet cemented on the drain plug provides an early warning of serious engine problems. It works. The first warning of a potential cam lobe failure was a metal "mud" made of fine particles clinging to the magnet. The cam wear problem was evident after the valve covers were removed, and one rocker arm was seen to be moving less than its companions.
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.
Removal of the intake manifold and then removal of the suspected lifter confirmed the extent of the problem. The lifter was so worn down that it was visibly shorter, and the bottom of the lifter was worn into a concave surface with sharp edges. Its cam lobe was equally bad.
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.
The wear pattern is a relatively straight band on these two other lifters, showing that they had stopped spinning. Flat-tappet lifters are designed to spin so that their crown wears evenly. If they stop spinning, cam failure is imminent. A likely contributing cause to this was use of synthetic oil, even though it was used only well after break-in.
Good news, bad news. The crankshaft journals were not damaged, but the bearings showed some contamination by metallic particles. One factor that helped save the engine from further damage was that we were alerted early to a problem by the particles picked up by the magnetic drain plug.
Another oil option is buying racing oils, such as Valvoline Racing Oil, Joe Gibbs, or Brad Penn. Look for a label that specifically states something like "contains added zinc." It may also state "not for passenger cars" and explain that it may damage catalytic converters. This is not a problem for pre-'75 cars or other vehicles that don't have a catalytic converter.
Another option is buying from a specialty oil company that formulates oil with antiwear additives similar to the good old days. Call them with a credit card and they can ship oil to your door.
The second way is to supplement modern oils by pouring in a break-in additive from a camshaft manufacturer at each oil change. These can be ordered from cam manufacturers, from speed parts distributors such as Summit Racing or Jegs, or picked up at local speed shops. Because formulations change, the safest policy is to check with suppliers of diesel oil, racing oil, or cam break-in additives to learn the current concentrations of their antiwear additives.
This modification of the oil filter mount helped protect the rest of the engine from the metal particles. The oil bypass valve opening was cemented shut with an epoxy to prevent any oil from bypassing the filter. The valve was originally intended to prevent oil pressure from dropping if the filter became clogged, but it's unnecessary when the oil is changed frequently.
Synthetic Oil
There are two sides of the argument about the danger of running synthetic oil in a flat-tappet cam engine.
The pro-synthetic oil argument is simple: thousands of people have run synthetic oil in flat-tappet motors with no problems (yet). But remember this is anecdotal; there are no long-term real-world tests across a variety of engines, and almost certainly there will never be any. Plus, just because many have run synthetic oil without a problem, that doesn't prove there isn't a higher risk factor.
With the pan off, this was a good time to change a drippy rear main seal, particularly since the bearings were also being replaced. A common problem with a rear seal is that its lip can wear into the crankshaft, and this area is not cleaned when the crank is ground. Felpro solves this by offering an offset seal (PN BS 11829-1) that has the seal lip in a slightly different location.
The "be wary of synthetic oil" argument has a couple facts. First, we know that synthetic oil is more slippery than conventional oil (which oil-heads nickname "dino" oil for dinosaur). This sounds good but actually may not be good for flat-tappets. For some background, flat-tappets are not completely flat. They have a very slight crown ground into their face. Also, each cam lobe is slightly tapered toward the front, and the lifter bore is slightly off-center on the cam lobe. These three things are done to make the lifter turn when the cam lobe slides on it. If the lifter stops turning, the cam lobe wears on the same area of the lifter and both wear down soon thereafter. Synthetic oils are so slippery that there is less force to turn the lifter. So, theoretically, synthetic oil could cause problems for flat-tappet cams.
The real-world warning comes from cam manufacturers. Who has better experience than the people who make cams, test them, and learn of failures because they warranty them? Major aftermarket cam manufacturers state not to use synthetic oil during break-in, and one states not to use synthetic oil for at least 5,500 miles after break-in of flat-tappet cams.
The one-piece rubber oil pan gasket from Felpro has been praised by a number of rebuilders. It comes with clever plastic studs to hold the gasket in place on the block while the pan is being installed. Silicone gasket sealer is used only on the four corners. The '74-and-up pans used a different thickness end gasket.
This writer switched to synthetic oil well after break-in, and subsequently lost a cam lobe at 4,500 miles. Inspection of the wear pattern on the other lifters showed three that were not turning.
Amsoil, the inventor of true synthetic oils, is aware of the flat-tappet cam problems and offers several oils with high phosphorus levels (over 1,250 ppm) and zinc levels (over 1,350 ppm). AMO 10W-40 and ARO 20W-50 Synthetic Premium Protection oils are recommended for flat-tappet and late-model high-performance motors. Amsoil's TRO 20W-50 Premium Synthetic Racing oil is recommended for highly modified, high-horsepower street or race motors. AHR Synthetic SAE 60 Racing oil is recommended for nitro- or alcohol-burning motors to protect from oil dilution by fuel. HDD Series 3000 Synthetic 5W-30 diesel oil also offers extra protection from high soot loading and acid generation in modern diesel engines.
The Comp Cams retro-roller lifters come in an assembled pair, connected by a link bar to prevent them from rotating. While flat-tappet rollers must rotate to ensure cam life, roller lifters absolutely must not rotate. Another notable difference is that used flat-tappet lifters should never be run on a different cam (or even a different lobe), while used roller lifters can be run on different cams.
If you think the lobes on the Comp Cams roller cam look meatier, you're right. Even though the duration and lift specs are similar to the flat tappet cam, the lobes are visibly wider at the top in profile on a roller cam.
Offshore Lifters
As roller lifters became the choice for auto manufacturers, the quantity of flat-tappet lifters that were needed dropped dramatically. The few companies making these lifters in the U.S. decreased their production, and one discontinued production. Eventually, flat-tappet lifters were in short supply and unbranded offshore lifters filled the void. Hold the mail, I am not saying that all U.S.-made products are perfect and all offshore products have problems. Japanese manufactured products have established a reputation for high quality, but many other offshore countries have not yet achieved such a reputation.
If your car occasionally gives a puff of blue smoke upon starting or after letting off on a long exit ramp, this is the perfect time to change valveguide seals. Choices include the umbrella seal that moves up and down with the valve, the original factory o-ring, and varieties of positive seals. The seal on the right presses onto the head's valve boss; in this case machined down to 0.500-inch diameter.
The point is, a change has occurred. Years ago, nearly all flat-tappet lifters sold in Amercia were made by a few U.S. companies that were well established, well respected in their field, and had decades of experience. Today, lifters from other companies are in the marketplace. make sure you know the source of the lifter and the reputation of the actual manufacturer, not the distributor. A lifter is a highly stressed part, and its demise can be very costly.
Our primary goal here is to warn readers who own flat-tappet cam engines that there are new choices to be made concerning the oil that's put in the crankcase in order to avoid premature cam failure. A second goal is to inform readers who are thinking about rebuilding their motors that there are new cam and lifter choices to help ensure long engine life using the newly formulated oils. One of these choices is installing a retro-roller cam. This is becoming more popular because it eliminates concerns about early cam failure caused by use of the newly formulated or synthetic oils, and it eliminates the flat-tappet cam break-in procedure. Follow along as we repair the damage from a premature failure of a flat-tappet cam and install a new Comp Cams retro-roller cam and valvetrain.
Degreeing the cam is not essential, but it will ease any worries about a problem with the cam or the timing gear. With the heads on, degreeing takes a $10 TDC stop tool, and then buying or borrowing a $25 degree wheel and a dial indicator with base. An hour of work here can prevent diagnosis dilemmas or parts problems that are more costly in the future.
Installation And Break-In Tips
Clean and inspect parts thoroughly, even though they are new.Apply cam lube on cam lobes, distributor gear, and lifter faces (not on the sides of lifters).Apply engine assembly oil on cam bearings, crank bearing, pushrods, and rocker arms.Apply regular oil on the lifter sides and use it in the motor. Thirty-weight is a good choice.Oil-prime the motor until oil flows from the top of all the pushrods.Do not run synthetic oil during break-in.Change oil and filter immediately after break-in. (I recommend this after 30 minutes or less on any rebuild.)
Installation of a cam thrust button is recommended when switching from a flat-tappet cam to a retro-roller cam. In a flat-tappet Corvette engine, the taper of the cam lobe exerts rearward pressure on the cam, as does the distributor gear that drives the oil pump. Comp Cams offers stamped-steel covers that look original, but are reinforced inside for the thrust button.
The following extra steps are only for flat-tappet cams; they are not needed for roller cams.
Install only the inner springs or install softer springs for break-in if you are using high-pressure springs.Make sure the engine is ready to start immediately and run continuously thereafter.Start the motor and then raise the rpm to 2,000-2,500 for 30 minutes (per Comp Cams).Mark the tops of pushrods and watch to make sure they are spinning.If the pushrods aren't turning, try to turn them as a last-ditch effort to get the lifters to rotate.
The roller lifters were soaked in motor oil and installed along with the valvesprings, rocker arms, and pushrods. The heads do not have to be removed to change valve-springs or valveguide seals; a bungee cord or air pressure can be used via the spark plug hole to hold the valve up.
<strong>Lube Lessons</strong>Watch out for the "gear" logo on conventional oils if you have a flat-tappet cam engine, such as Corvettes prior to 1987. Many of these oils have significantly reduced levels of special antiwear additives that can be critical to your engine's health.