Compared to the old, stock Gen I/LT1/LT4 small-block valvetrains, the LS engines are head and shoulders above their ancestors when it comes to factory equipment. Where the old engines (except the LT4) used stamped steel rocker arm bodies that had wide ratio tolerances around the centerline of 1.5, the LS engines use cast steel bodies with much less variance from the specified 1.7 factory ratio. LS rockers use a roller trunnion, where Gen I/LT1/LT4 used a pivot ball assembly. LS engines also use a net-lash, non-adjustable system for securing the rockers and setting lifter preload, where the old engines used an adjustable system that could be used with either hydraulic- or solid-lifter camshafts.
But the LS system isn’t without its own weaknesses, the most critical being the bearings on the rocker arm trunnions. For those not versed in valvetrain terminology, the trunnion is the shaft the rocker arm pivots on. On older small-blocks, the factory stamped steel rocker arm would rotate against a pivot ball, with a film of oil between the two for lubrication. This was a high-friction design that left a lot of room for improvement, creating the market for high performance roller rockers.
Note: When someone says “roller rockers” there’s a common misconception this refers to the roller tip on the rocker arm body. Roller refers to the roller bearings used on the rocker arm trunnion to reduce friction and increase high-rpm durability and horsepower.
In stock applications, the factory LS rocker bearing does just fine. But when higher-lift camshafts, higher spring pressures, and stiffer pushrods are used, the amount of stress exerted on the factory trunnion bearings increases substantially, especially in high-rpm situations. Under these stresses, the factory roller bearings can fail, and because of their uncaptured design (explained in the photos ahead) the needle bearings are ejected into the engine oil, leading to complete valvetrain and engine failure.
Previously, the only way to prevent this from happening was upgrading to either aftermarket roller or shaft-mount rockers. Both options involved considerable expense, and also required extra parts because they eliminated the net-lash system and required the installation of new rocker arm studs and adjustable rocker nuts. Converting an LS engine to an adjustable valvetrain is an advantage of this, but for most guys with mildly modified engines, unnecessary.
To fill the gap between stock rockers and fully adjustable roller rockers, the valvetrain gurus at Comp Cams came up with this nifty trunnion upgrade kit. With a retail price of just over $100, the kit comes with upgraded trunnions, captured needle roller bearing assemblies, and works with any factory LS rocker. That’s right, this kit works even with the offset LS3/LS7/LS9/LSA rockers. And because the factory net-lash system is retained, you don’t have to worry about resetting lifter preload, making the job that much easier, especially for novices.
Follow along as we show you just how simple this upgrade really is. And to see a quick video of this swap taking place, point your web browser at http://youtu.be/IcLAh8J6tPs.