There hasn’t been a cast-iron flat-tappet-lifter engine developed by original equipment manufacturers (OEM) since the ’80s, yet hundreds of thousands are still on the roads. For years since then, these lifters have been made for the aftermarket by the same manufacturers who supplied the OEMs. With the pandemic, workforce changes, and supply chain material issues, these manufacturers have struggled to keep up with demand. In the wake of these challenges, COMP Cams went looking for a solution and found it with the development of a Diamond-Like-Carbon (DLC) coating for lifters.

We sat down with COMP Cams Valve Train Engineering Manager, Chris Potter, to understand what the new DLC lifters are all about and how they proved to be a game changer for those still using traditional OEM engines. Through the process, we learned that way more research, development, and testing go into that little, round hunk of metal than the average Joe could ever imagine.

Lifter Education

Before we get into DLC and why it works, we need to give a little tutorial on what a lifter is and how it works. Lifters are built specifically for one of two types of cams, either flat tappet or roller. They play a crucial role in the valve train as they convert the camshaft’s rotation into linear motion, which actuates the rocker arms to open and close the intake or exhaust valves.

There are two types of lifters — hydraulic or mechanical (solid) — yet, either can have a flat or roller tip. The difference between the two is that a mechanical lifter is a solid piece of metal with no preload, so they require someone to set the valve lash manually. On the other hand, hydraulic lifters are self-adjusting by using a valve-controlled plunger within the tappet body. It preloads the pushrod through oil system pressure to maintain the valve lash in the closed position. This article concentrates on hydraulic flat tappet lifters designed to work with flat tappet camshafts.

Despite the flat tappet name, neither the cam lobe nor the bottom face of the lifter is flat. Although it is virtually impossible to see with the naked eye, the lifter face is actually crowned, while the cam lobe is slightly tapered (usually toward the rear of the engine). There are two reasons for the shapes, which are critical to the function and relationship of the two parts.

Because of the way the taper and crown come together, it causes the lifter to spin in the bore. The spinning action ensures even wear of the surfaces, allowing the lifter to live a long life. On most non-roller engines, especially Small-Block Chevys, the taper on the lobe is lower toward the front of the engine and higher at the rear. This helps locate the cam, keeping it pushed into the block. The combo works terrifically and has been utilized almost since the invention of the internal combustion engine.

Causes of Lifter Failure

Flat tappets’ efficiency and longevity rely on a clean environment, proper oiling, spring pressure, and break-in. A shortcoming in any of these areas can cause failures, some faster than others. However, improper break-in is probably the number one cause of cam failures, and it could occur within the first 50 revolutions of the engine.

Break-in is the most critical, as it “mates” the cam lobe to the lifter surfaces and seasons both. The cam lobe and lifter surfaces develop a wear pattern that uniquely identifies what lobe the lifter belongs to. It’s not noticeable to the naked eye, but it is essential to the part functioning correctly. The break-in procedure is also why you should never buy used lifters or even use a lifter in a different bore than the one in which it was “born.”

Potter says the highest cause of lifter failure is trash getting caught in the system. It could be a metal shaving, dirt from a rag, or even a piece of silicone that didn’t get cleaned up during the engine build. Metal shavings tend to cause issues on the bottom side of the lifter by getting trapped between the two faces, causing the lifter to stop spinning or welding themselves to one of the surfaces. Either way, it will begin to wipe the lobe. It will continue to get worse, and there will be no return.

On the other hand, silicone usually causes problems at the top of the lifter where the plunger functions, as it can get trapped in the oil passages. This can cause the lifter not to fill quickly or entirely enough (collapsed lifter). Anything that keeps the lifter from spinning can cause a failure, and it doesn’t take long to start the damage. However, it could take some time to discover if you aren’t completely in tune with your engine.

 

Potter says that one of the biggest misconceptions for lobe or lifter failure is a “soft” cam or improper heat treatment. People will often blame a wiped lobe on the heat treat. “It is virtually impossible to have a ‘bad heat treat’ on a cast iron cam,” he says. “The heat treatment is done before the cam is ground and penetrates almost to the core. If you truly had a soft-cast camshaft, we would catch it because it wouldn’t grind properly. The metal would start galling, spawling, or falling off. It wouldn’t be able to make it out the door.”

The Problem With Cast Iron

Traditional flat tappet lifters are made of cast iron — an extremely strong, hard, and durable metal. Cast iron used to be plentiful; cams and lifters have been made with it for years. It is an excellent material to make these parts from as it has a high compressive strength (resistant to dents and bending) and should last an incredibly long time unless it isn’t broken in properly or something foreign is introduced to it.

The problem with traditional cast iron flat tappet lifters is that the manufacturing process is critical to ensuring they are compatible with cast iron camshafts. When material shortages hit foundries, it caused a ripple effect. Foundries had to change the recipe of the metal or quit making cast iron parts altogether. Inconsistent recipes can lead to inconsistent results or unforeseen consequences for those making parts from them. The shortages and inconsistencies had COMP Cams engineers looking for a solution.

Changing Directions

One might wonder why not just switch to steel and call it game over. That is a valid solution for some but not a realistic one for many, and for multiple reasons. Firstly, we already mentioned the compatibility of the metals — a cast iron cam would chew apart a steel lifter in no time. There are thousands of engines still running cast iron cams and lifters; it would require customers to convert their entire valve train over to steel. Secondly, many race classes are using these engines that require the use of a cast iron cam. The rules do not dictate lifter material, but by default, that meant using cast iron lifters. Until now!

COMP engineers asked why not use a steel lifter with a coating that could withstand the rigors of a cast iron cam. They were aware of a solution, but would it work? This coating has been used with great success for quite a few years in the space, tooling, computer, medical, gunsmithing, and automotive industries. High-end racing series like F1 and NASCAR use it. COMP has even been using it on solid lifters for high-end race applications as well. But it was expensive, putting it out of reach of the target market for hydraulic flat tappet users.

Introducing DLC

That coating is Diamond-Like-Carbon (DLC). Without getting too deep into the science, DLC is a class of amorphous carbon materials that display some of the properties of diamonds. It is an extremely tough, durable, slick, and wear-resistant coating. DLC doesn’t penetrate the metal; it permanently adheres to it through a vapor deposition process. It is microns thick and is incredibly hard compared to the camshaft material. There are two significant challenges to using DLC — expense and production process. Also, the part must have a perfect surface finish underneath and a very hard material to support the DLC.

“Basically, all the substrate has to be perfect for it [DLC],” Potter says. “If you have a rough surface finish on a piece of steel and you DLC coat it, it’s going to turn it into a file. It will start removing material, becoming a file that will never wear down because it will always be harder than what you are rubbing it against. So, the processing is critical on these.”

COMP partnered with its vendor to make a premium steel body with DLC on the face of the lifter. COMP engineers worked hard to get the surface finish they wanted and the crown on the bottom of the lifter to match their specifications. By all standards, you wouldn’t be able to tell the difference between the High Energy cast iron lifter (P/N 812) and the High Energy DLC lifter (P/N 812D) other than the darker, albeit shinier surface on the bottom of the DLC parts — everything else is exactly the same.

Though DLC is an expensive process, the product’s popularity in such diverse industries has brought the price into reach for an average Joe. Because of the high volume COMP sells annually, they were able to get the lifters coated relatively inexpensively for customers. A set of 812D lifters is approximately $20 more than the traditional 812.

The High Energy DLC Flat Tappet lifters maintain the excellent mechanical and hydraulic performance that traditional High Energy Hydraulic lifters provide. DLC reduces friction due to its high lubricity and wear resistance, extending the life of the lifter and cam. Though DLC virtually eliminates the need for the traditional break-in procedure associated with cast iron for the lifter, COMP does not recommend skipping the process because it is still necessary to establish its wear pattern with the cam lobe. However, Potter says the coating is more forgiving should you get it wrong.

Why Not Just Switch?

It is immediately apparent that DLC is a premium option at a fraction of the price, but you may be wondering why someone would still buy cast iron. There are two significant reasons: class rules and cost. Some drag racing classes require participants to use a flat tappet lifter, leaving racers with no choice in materials. DLC allows them to run a cast iron cam and go with an inexpensive (compared to roller) steel-core DLC lifter while pushing the envelope on spring loads.

Though it will likely change, cast iron is still a cheaper option, especially if you plan on a budget build. While it is true that steel cams and roller lifters typically have a much more robust design, the industry has proven that cast iron flat tappet cams and lifters are more than capable of meeting the performance and reliability demands of most customers.

COMP’s DLC flat tappet lifters are the next step in maintaining affordability for the flat tappet market for hot rodders and racers alike. If you are looking for a less expensive option that is more forgiving and will last longer or are running a class that mandates running flat tappets, DLC is definitely the way to go on your next engine build. Give the COMP Cams tech line a call to find out if DLC lifters are the best option for you.