1. The Comp Cams kit (PN K11-413-8), which included an Xtreme Energy hydraulic roller camshaft, roller lifters, valvesprings, push rods, a timing set, and even a cam button, which is necessary on Chevy engines converting to a roller cam.

Hydraulic Roller Camshaft Swap

BY BARRY KLUCZYK PHOTOGRAPHY BY THE AUTHOR

teven Nissen rolled his 1971 big-block Chevelle into Stellar Rod & Custom with a seemingly simple request: Swap the old carburetor for fuel injection. The Detroit-area shop obliged and installed an Edelbrock EFI system.

But there was a problem. As soon as Stellar connected the control system and turned the ignition key, the engine began popping and even backfiring through the throttle body. It wasn’t a tuning issue, and what Nissen previously thought was an out-of-tune carburetor or bad ignition timing pointed to a different culprit.

“We knew right away something else was going on,” Stellar owner Mike Brimm says. “The engine had been rebuilt and didn’t have many miles on it, but the exhaust pops seemed to suggest the valve timing was off. It could have been a sticking valve, but the engine also had a flat-tappet camshaft; the bigger worry was its lobes and lifters.”

After removing the valve covers, a few of the rockers appeared to be a little lazy when the engine was running, indicating the valves weren’t opening or closing properly. A follow-up inspection with a borescope revealed jagged edges on a couple of the lifters. Three of them had “mushroomed,” too. Not good.

After that troubling discovery, Nissen had the Stellar team remove the engine and inspect it. When the camshaft was taken out, Brimm’s concern was confirmed: several lobes were destroyed, and the cam was unusable. There were many possible reasons the flat-tappet (mechanical) camshaft could have failed, but the most likely cause was a lack of zinc in the motor oil. Zinc is essential for preventing wear in a flat-tappet valvetrain.

It would have been easy to slip a replacement mechanical camshaft into the block, but switching to a hydraulic roller camshaft made more sense. Flat-tappet supporters will argue about the performance benefits, like greater lift and higher rpm potential, but Nissen’s A-body was just a street cruiser, so those factors didn’t really matter.

In fact, without the need for periodic valve-lash adjustments or concerns about “wiping out” the lobes—assuming the camshaft was installed and broken in properly—the low-maintenance nature of a hydraulic roller made it a much more practical choice. Additionally, the matching roller lifters would also reduce the load on the valvetrain, freeing up a few horsepower in daily driving compared to the flat-tappet design.

What’s not to like, right? Well, there are several considerations and upgrades to support when switching to a roller camshaft, and that’s the focus of this story. Along with the camshaft itself, nearly all the valvetrain components must be changed, along with a few other details—and if they aren’t done properly, the results can be as disastrous as a wiped-out flat-tappet camshaft.

“Timing is literally everything in an engine,” Brimm says. “All the valvetrain components must be spec’d perfectly to ensure valve timing is spot-on.”

For Nissen’s engine, Stellar went with an inclusive kit from Comp Cams, which included an Xtreme Energy hydraulic roller camshaft, roller lifters, valvesprings, push rods, a timing set, and even a cam button, which is necessary on Chevy engines converting to a roller cam. The kit is available directly from Comp and from popular retail outlets.

One thing not included, but essential for a roller cam upgrade, was the hardened drive gear for the distributor. Additionally, a hardened fuel pump pushrod is necessary for engines still using a mechanical pump, but since the engine in this project used an electric fuel pump for its fuel injection system, it wasn’t needed.

With all the parts on hand, the installation was fairly straightforward, but the rocker arms didn’t quite fit right. They were a bit wobbly, and it turned out the pushrods, while correctly sized for a stock engine, didn’t quite fit with the rebuilt big-block.

“We didn’t know the details of the rebuild, so we didn’t know how much the block and heads had been machined,” Brimm says. “Those details stack up on one another and can affect the valvetrain geometry. In some cases, you can make the stock-length pushrods work, but in this case, we needed an all-new set.”

After that was sorted, the engine went back together, and Nissen’s Chevelle was running better than ever. The maintenance-free hydraulic roller cam, combined with the engine’s EFI system, gave the classic A-body a contemporary rejuvenation, but Brimm reminds us that nothing in vintage car projects should be taken for granted.

“From the original issues that revealed the bad camshaft to selecting the right cam kit to even determining the correct pushrods, you can’t make assumptions,” he says. “Every step requires careful examination, preparation, and execution.”

We couldn’t have said it better ourselves.

2. Backfires and a popping exhaust were clues that not all was right with this big-block Chevy 402, which was powering a 1971 Chevelle that had just received an Edelbrock EFI upgrade.

4. Nothing triggers a sinking feeling quite like discovering particles on the oil pump pickup. This engine had them and, after seeing lifter issues with a borescope, it all but confirmed the camshaft was a goner.

6. Leaving the rod-and-piston assemblies in place saved time, but care was taken to protect the rod ends. Snipping off and slipping on a few lengths of fuel hose did the trick.

8. There are seemingly countless options for camshaft upgrades, and for this essentially stock combination, Comp Cams’ kit (PN K11-413-8) was selected. It included an Xtreme Energy 212/218 hydraulic roller cam, along with lifters, pushrods, valvesprings, a timing set, and more.

10. Roller lifters offer less friction, require less maintenance, and last longer. For this project, the kit included Comp Cams Evolution lifters with link bars (PN 85401-16).

12. The cam bearings didn’t look bad after removing the flat-tappet camshaft, but for about $40, replacement was cheap insurance.

14. For classic Chevy engines and some others, a roller camshaft needs a thrust button to control forward and backward movement of the camshaft. It isn’t necessary on a flat-tappet design because of the tapered lobes, but the flat surface of the roller tappet allows the camshaft to shift forward and back. This button was included with the cam kit.

16. Following the directions is perhaps most important when it comes to degreeing the camshaft—a topic suitable for a standalone story. More than optimizing performance, this crucial part of the process helps ensure proper piston-to-valve clearance.

18. Hydraulic roller lifters, like those in the Comp Cams kit, have link bars that connect the intake and exhaust lifters. Before installing, it’s a good idea to hone the lifter bores to ensure they have clean, smooth surfaces.

20. Here, all the lifters have been installed, and the new camshaft is visible through the oil drain holes in the block’s valley. Also, note that the lifters’ tie bars face the valley rather than the walls.

22. Just like with degreeing the camshaft, measuring the pushrod length involves many more steps. It includes marking the valve tip and checking the witness mark the rocker arm leaves after the valve opens and closes. Using a checking spring instead of the actual valvespring, as shown here, makes the process much easier.

24. With the correct pushrods in place, it’s time to set the preload for the valvetrain to zero lash. With the spark plugs removed, begin by rotating the engine to TDC on the compression stroke. Then, tighten the rocker until spinning the pushrod with your fingers creates slight resistance. There should be no lateral movement in the pushrod at that point. If so, zero lash has been achieved, and the rocker fastener is tightened another half-turn to set the proper preload. The same procedure applies to the rest of the valves.

26. Since most roller camshafts are made of billet steel rather than cast iron, their distributor gear can cause excessive wear against a standard, softer cast-iron distributor gear. Therefore, the distributor gear must be replaced with a hardened, melonite-treated steel gear, the most common and cost-effective option, like the one shown here. Bronze and composite gears are also available. Additionally, a hardened fuel pump pushrod must be used on engines equipped with a mechanical fuel pump.