Tech Stuff

Upgrading LS rocker arm trunnions: A necessary fix for an LS weak link

Text and photos by the author.

Highly regarded as “today’s” hot smallblock Chevy, GM’s family of LS engines represents a real milestone in performance V8 engine design. Even straight out of the factory, the LS (in all of its variants) produces decent power. The oiling and sealing systems represent drastic improvements over the early smallblock design, and they make great platforms for additional aftermarket power enhancements. It’s relatively easy to make these buggers scream, thanks in large part to the advanced cylinder head designs that were started by GM and further HP-injected via a wide selection of aftermarket heads. The performance aftermarket has a solid grip on the LS platform (and continues to develop go-fast components for the LS), making it easy to pump additional ponies and torque without gnashing your teeth or bruising your brain.

Overall, the factory LS engines offer surprisingly decent durability. However, in the process of building/modifying any performance LS engine, if you plan to use OE rocker arms (whether re-using originals or using new OE rockers), you should be aware of the critical need to perform an upgrade to the rocker arms. Specifically, the OE trunnions and trunnion bearings should be replaced with an aftermarket upgrade kit.

There’s really nothing wrong with GM’s original rocker arm design. The rocker arms are lightweight and stiff, and strong enough to withstand most high-performance street applications.

The bad news is that in high rpm situations and when used in conjunction with high valve spring pressures, the factory cageless trunnion needle bearings’s outer shell may tend to begin walking out of the rocker arm’s pivot trunnion bore, resulting in individual needle bearings quickly falling out and scattering throughout the engine (the OE needles are captured by two separate housings, and the outer housing tends to walk out, releasing the needles). Obviously, this isn’t good for either the rockers (no bearings) or the rest of the engine. And let’s face it — any performance-minded customers will stomp the throttle and lean on their engines from time to time, and it’s also very common for owners to pump up the volume by making a performance cam change (which in most cases will involve higher-than-factory valve spring pressures).

Note that the recommendation to upgrade LS rocker arm trunnions is not limited to performance enthusiasts alone. Any LS engine that will be exposed to abusive conditions will benefit from this upgrade. This can include LS engine applications for police vehicles and other emergency vehicles, as well as commercially used trucks that will experience heavy engine loads.

If, during an oil change, you find small “mystery” needle bearings in the oil or stuck to the magnetic drain plug, this is clear evidence of rocker arm needle bearing failure (the needles have left the rockers and are now wiggling around on top of the heads and washing down through oil drain back holes on their way to the sump. And along the way, who knows what little orifices they’ll migrate into (a scary thought). As I mentioned earlier, this condition, although possible in any daily driver, is more prone to occur if the engine is operated at frequently high engine speed, and/or if high valve spring pressures are used (as when changing over to a hotter cam that includes higher-rate springs). This warning bears repeating. The inexpensive OE rocker arm bearing setup is a proven weak link in the LS system.

Post a comment

Comments (1)


Post a Comment

Subscribe Today

Subscribe to Auto Service Professional

Sign up for a FREE subscription to Auto Service Professional magazine