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.
Knowing that this possibility exists, the best course of action is to address the issue before it becomes a problem, either by changing to high quality aftermarket performance full-roller rockers (any reputable aftermarket rocker manufacturer will use high quality caged bearings in their rockers), or by upgrading the original rocker arms. Especially for those on a limited budget, upgrading the OE rockers is an excellent option.
Comp Cams, as an example, offers a very high quality trunnion bearing upgrade kit, part number 13702-KIT. This kit, applicable to LS1/LS2/LS3/LS6/LS7 OE rockers, includes new trunnions, new caged and prelubed bearing assemblies, circlips and rocker arm mounting socket head cap screws (along with two thick installation-assist washers). The new trunnions feature extended tips with circlip grooves. Instead of the bearing housings relying on a press fit, the additional circlips serve to prevent possible bearing assembly walk-out. These bearings aren’t going anywhere, so the rocker bearing issue is no longer a concern. The new trunnions and bearings are also made of higher quality materials and are designed to withstand higher RPM and high spring pressures.
Comp’s upgrade kit replaces the (cheap) cageless OEM needle bearing assemblies and powdered metal trunnions with very high-strength premium 8620 steel alloy trunnions and fully-caged roller bearings for vastly-improved durability. According to Comp Cams, this rocker arm upgrade has been tested and performance-proven for several years in the NASCAR GM LS spec engine series.
If your customer intends to “play” with his/her LS engine and they plan to use OE rockers, upgrading the trunnions is a MUST-DO modification to avoid potentially catastrophic engine damage.
NOTE: While you can change-out the trunnions and bearings using a hydraulic press, a specialty tool designed for use with a common bench vise was recently introduced by Summit Racing. Their new rocker arm vise tool, P/N SME-906011, makes this job a breeze, and is ideal for removing the OE bearings and installing Comp Cams’ trunnion upgrade kit. This is the tool that I used during the upgrade pictured in this article.
By the way, if you need a set of new GM rocker bodies, Summit also offers an eight-pack of new, shot-peened GM rocker bodies (without bearings, so there’s no need to press out the old ones). These rockers (eight-pack) are available under Summit’s P/N SME-143000. The vise tool was developed by Summit’s Trick Flow division, and works like a charm.
TRUNNION UPGRADE PROCEDURE
Performing this retrofit upgrade is relatively simple, requiring no modifications to the rocker arm. While you can perform the job with a punch, a press or vise, an appropriate-size socket and snap ring pliers, Summit Racing has recently introduced a very cool specialty tool that allows you to get the job done using only their kit, a bench vise and snap ring pliers.
In this article’s example, we took advantage of the new Summit rocker arm vise tool, which includes all tools needed to remove the OE bearings and install the upgrades.
By the way, this is a good time to clean the rocker arm bodies. If you want the rockers to look factory-fresh, clean with solvent, or have them professionally tumble-cleaned with a fine-grit stone, or you can glass bead blast the disassembled bare rocker bodies. If you do decide to blast with fine glass bead, be careful not to concentrate and dwell any blasting in the trunnion bores or on the valve tips or pushrod cups. Do not run any type of hone or reamer in the trunnion bores. If trunnion bores appear to be damaged (burred, scored or pitted), replace the rocker arm. You must avoid altering the trunnion bore dimensions.
1. Place the Summit tool vise fixture onto one jaw of your bench vise. Place the OE rocker into the fixture’s V-saddle.
2. Align the (black) Summit presser to the OE bearing, with the counter bored end of the presser facing the bearing. Tighten the bench vise to press-out both OE bearings and the trunnion (needles will fall out). Inspect/clean rockers as needed.
3. Place the (black) presser onto the short end of the kit’s mandrel. Slide a new bearing onto the long end of the mandrel (make sure that the stamped symbols on the bearing faces the mandrel’s flange).
4. Slip the aluminum alignment sleeve onto the long end of the mandrel, seated against the bearing.
5. Slide the mandrel assembly into the rocker arm bearing bore (the aluminum alignment sleeve enters the bore first to align to the rocker body).
6. Using the bench vise, press the bearing into the rocker body until the mandrel’s flange bottoms out onto the rocker body. Perform this single-bearing installation to all 16 rockers before proceeding with trunnion and opposite-side bearing installation.
7. Place the rocker arm body onto the Summit vise fixture, with the previously-installed bearing facing the fixture.
8. Slide the new trunnion halfway into the bearing bore (leaving the outside end of the trunnion exposed to align the remaining bearing). Apply engine oil to the outside of the bearing. Slip the remaining bearing onto the exposed trunnion (make sure that the stamped symbols on the bearing cage face outward).
9. Place the kit’s thick steel washer onto the end of the trunnion (against the bearing face).
10. Tighten the bench vise until the washer bottoms out against the rocker body.
11. Verify that the trunnion rotates freely, and that a slight amount of endplay (side-to-side) exists, in the range of 0.004 - 0.008 inch. If you don’t have any endplay, adjust bearing depth accordingly.
12. Using snap ring pliers, install one circlip to each end of the trunnion. Verify that the clip is fully seated in the trunnion clip groove.
13. Install the upgraded rocker arms to the cylinder heads using the new socket head cap screws supplied in the Comp Cams kit.
Be sure to rotate the trunnion so that the flat recess side of the trunnion’s bolt hole faces upward (the socket head cap screw must seat against this recessed flat side of the hole). Tighten the cap screw to a value of 22 ft.-lbs., following the OE installation procedure.
NOTE: Install the new upgrade kit using either a press or with Summit’s new rocker arm vise tool. It’s critical to smoothly draw the OE bearings out and draw the new bearings in. Do not try to bang the old trunnions out or attempt to install the new bearings with a hammer. Leave your hammer in the toolbox.
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Available trunnion/bearing upgrade items
Item / Manufacturer / PART NO.
Rocker arm trunnion upgrade / Comp Cams / 13702-kit
Rocker arm vise tool / Summit Racing / SME-906011
New shot-peened GM rocker bodies (w/o brgs) / Summit Racing / SME-143000 (eight-pack)