The Comp Cams trunnion (bottom) is an alloy steel unit that places the full load of the rocker arm on a 360-degree surface area. Compare that to the factory, powdered metal trunnion (top) that places the rocker arm load on half as much surface area. The bearings in the Comp kit are also fully captured, with the trunnion and bearings held in place by a heavy duty snap ring.
*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.
Comp Cams trunnion upgrade kit, part number 13702-KIT, comes complete with everything needed to upgrade all 16 rocker arms. The kit has seen widespread use in NASCAR, NHRA, IHRA, and other forms of racing where the stock rocker arm body must be used.
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.
On the left is a rocker arm with the Comp Cams trunnion upgrade kit installed, on the right a bone stock factory rocker arm.
The factory trunnion setup uses a stamped cap to keep the trunnion and bearings in place. In high performance, high-rev applications, the movement of the rocker arm along with normal operational vibrations and energies transmitted through the valvetrain can cause the trunnion to move laterally inside the rocker arm body (or the rocker arm body to move laterally on the trunnion) and eventually press the retaining cap out of the body, which then releases the needle bearings into the engine and oil.
This rocker arm came out of an LS3. After a few track days the engine suddenly developed a miss, and the owner feared a piston or other major internal component had failed. What had really happened was the rocker began moving from side to side on the trunnion and wasn’t opening and closing the valve properly. Fortunately the owner shut the engine down before the trunnion had come fully loose and ejected the needle bearings into the oil.
When the retaining caps come loose from the rocker arm, this is what gets ejected into the oiling system. Sometimes the screen on the oil pickup will catch the needles and keep them from being sucked through the full oiling system, but not always.
The Comp Cams trunnion (bottom) is an alloy steel unit that places the full load of the rocker arm on a 360-degree surface area. Compare that to the factory, powdered metal trunnion (top) that places the rocker arm load on half as much surface area. The bearings in the Comp kit are also fully captured, with the trunnion and bearings held in place by a heavy duty snap ring.
Changing the trunnion in an LS rocker arm is easy. The factory trunnion can be tapped or pressed out, and Comp has a special tool to aid in the removal of the old trunnion that also helps when installing the new bearings and trunnion.
With the Comp 13702-Kit, the trunnion cannot move inside the rocker arm body thanks to the snap ring retention system. Not only does this eliminate the chance of the trunnion pressing the bearings out of the rocker arm body, it also maintains proper rocker arm alignment on the valve stem, which can cause a whole other set of potential problems. The Comp trunnion kit also reuses the factory net-lash rocker arm retention system, so reinstallation of the rockers is a breeze.
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.
