*photography by: the author
Ironing out Weaknesses in the LS-Series Rocker Arm
While the excellent design and capability of the LS-series V-8 has been well proven after a decade and a half of production, it still has a few small weaknesses that can lead to trouble in a performance application. One of those is the rocker arm trunnions.
First, a little design history. The valvetrain in the LS series (and next generation LT series) is a net-lash design. This means that the valvetrain is not adjustable from the factory, and each rocker arm is secured to the head by a bolt that when tightened properly, sets the lash/lifter preload to factory spec. This was done to cut down on engine assembly time and costs.
Unlike the Gen I and Gen II small-blocks, which used a 1.5 ratio stamped-steel rocker arm and pivot ball from the factory (except LT4 engines which came equipped with factory roller rockers), the LS series uses a 1.7 ratio diecast, ductile iron rocker arm body with a needle bearing equipped, powdered metal trunnion to reduce friction and wear.
The Achilles heel of this design is in the needle bearing package and trunnion. The needles are uncaptured inside the bearing retainer. Where the failure occurs is when the rocker arm trunnion begins to press the bearing pack out of place inside the rocker arm body, eventually leading to the needle bearings being ejected into the oil and sucked through the oiling system. This can lead to engine damage and possible failure.
To solve this problem, Comp Cams designed a trunnion upgrade kit, part number 13702-KIT, that eliminates this potential problem. The kit utilizes a much stronger alloy steel trunnion in place of the factory powdered metal unit, along with fully captured needle bearing sets held in place in the rocker arm body by snap rings. The new trunnion also allows for 360-degree travel of the rocker arm, spreading the load on the trunnion bearings across a much greater surface area, which reduces wear on the bearings and trunnion.
The kit typically retails for a little over $100 and is available direct from Comp or through most retail performance outlets like Summit Racing and Jegs. That’s a small price to pay when compared to the repairs that are typically needed when a rocker arm fails on a running engine.
Patrick Hill has grown up around the automotive aftermarket, and carries a lifelong passion for performance, racing and automotive nostalgia that spans from the Tri-Five era to the current modern performance market.