One of the roller lifters...
One of the roller lifters had failed. Most of the time when a roller lifter breaks, the bearings have failed and the wheel locks. Once the wheel stops turning, the engine becomes a lathe, grinding down the lobe on the camshaft. Not only does this trash the cam and potentially damage the rocker arm, pushrod, and valve when excess lash is introduced, it also sends metal throughout the engine. That's what we call a bad day.
The challenge in using race-bred valvetrain parts on the street boils down to the individual parts being at odds with each other. To make maximum power, a roller camshaft snaps the valves open and closed very quickly. This places immense side-loading force on the lifters, literally forcing them up by squeezing them against their bores. In addition, the valvespring pressure is very high in order to control the valves as the cam cycles them. If the springs aren't matched to the cam profile and the maximum rpm of the engine, the valves can actually bounce when they close, and the lifters won't stay on the cam lobes. This is bad for power, and it can be catastrophic for the engine. Even with the latest technology, a huge race cam on the street will eventually kill a set of lifters. In fact, Kurt Urban recommends we replace the lifters in this engine after 5,000 street miles or immediately if we find that the valve lash loosens up. While we're at it, the valvesprings should be checked each year, and replacing them before seeing hard racing use is a wise choice. How big is too big? It's best to work with a knowledgeable team like the folks at COMP Cams to make that determination for your specific application.
With the valvetrain completely...
With the valvetrain completely disassembled, we called COMP Cams to get the skinny on the latest valvetrain technology for these older engines. In addition to quite a few solutions for our situation, the company also just introduced some very cool die-cast aluminum, black-wrinkle big-block Chevy valve covers, and their own blend of break-in oil that address the needs of bearings and rings as well as sensitive new valvetrain components.
Most engine builders opt for more moderate cam specs on an engine that will spend most of its life on the street. Sure, you'll give up some power, but you have to weigh the pleasure of hassle-free street driving with maximum horsepower at wide-open throttle. Just as important as the cam specs is the basic type. A roller camshaft will make more power because of the steep ramps that are possible, but should you use a solid roller or hydraulic? A long time ago, a roller lifter cam meant constantly checking the valve lash-the clearance between the rocker and the valve tip. In a solid lifter setup today, that's still true. The advantage of a solid lifter, in addition to maximum power, is that the valve lash is a great canary in the coal mine. If you find more clearance, something is wearing or broken, and you need to inspect the rocker, rocker mount, valve tip, and lifter. If you suddenly have less clearance, you probably have a valve that's mushrooming, and it's time to pull the heads. Hydraulic lifters absorb some of the beating within the valvetrain, especially the bearings in the roller lifters themselves. They also alleviate having to periodically check and adjust the valve lash. Matt Summerfield at COMP really would have preferred that we use a hydraulic roller cam with 266/274 degrees of duration at .050 and .646-/.646-inch lift for this engine. This would have greatly extended the life expectancy of the lifters and would make the valvetrain virtually maintenance free.
Starting with the bumpstick,...
Starting with the bumpstick, Matt Summerfield at COMP Cams walked us through the new profiles that decrease the stress and wear on the lifters. These new profiles also require less valvespring seat pressure, which decreases stress on everything in the valvetrain. To visualize and simplify the difference in profiles, look at the old camshaft (left) that had lobes that were more rectangular in shape. This pushes the lifters sideways in their bores, literally squeezing them upward. The newer profile (right) has slightly more angle to the ramps, lowering the side-loading of the lifters. Naturally, this comes at the expense of duration, but the new profile minimizes the power loss of a "smaller" cam.
One thing that hasn't changed...
One thing that hasn't changed in roller camshaft technology is the distributor drive gear. You want to make sure you get an iron gear, which will happily mesh with a standard distributor gear. Since roller camshafts come from a race lineage, most aftermarket roller cams will require that you install a sacrificial bronze distributor gear if you don't specify an iron gear. The bronze gear on the distributor is softer than the camshaft so that it wears instead of the cam gear. This means one more thing to inspect and periodically replace if you don't have an iron gear on the cam.
The Elite Race solid roller...
The Elite Race solid roller lifters are the latest technology from COMP Cams for maximum durability in radical engines. The most significant strength improvements are a longer axle (0.400 inch) that is pinned in the body on both sides. The pins add strength, and they pressure feed oil to the axle and needle bearings. These lifters also use the highest grade roller bearings-as well as more of them-for improved load distribution. The bodies are made from 8620 steel.