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LS/LT Rocker Arm Trunions - How to avoid ruining your engine

One of the most common, as well as budget friendly modifications you can do to an LS or LT Chevrolet small block engine is upgrade the camshaft. The camshaft is connected, by a chain, to the crankshaft and controls all of the valve train events. The farther you open your intake and exhaust valves, as well as the valve timing and duration, can have a substantial effect on horsepower and torque. This is due to the fact that you are simply allowing more air into the cylinder, as well as creating a scavenging effect. Scavenging uses the exhaust gasses exiting the cylinder at a high speed to help pull fresh air/fuel into the cylinder.  

There are many supporting modifications that are generally performed along with a performance camshaft to properly capture the benefits provided. These usually focus on improving airflow to, and from the cylinder head (Cold air intakes, porting, headers etc.). There are also other mechanical upgrades that need to be performed as well to properly control valvetrain harmonics and characteristics (Stronger pushrods, valve springs, lifters etc.).

One very common aspect that is sometimes overlooked is the rocker arm trunion. This is the fulcrum of the rocker arm which is responsible for converting the upward motion of the pushrod into a downward motion of the intake and exhaust valves. The stock rocker arm is generally not required to be upgraded in most applications as it is very strong as well as lightweight, the focus is on the bearing pressed into the rocker arm (trunion).

The issue lies in the trunion itself. There are needle bearings in the trunion to reduce the friction of opening the valves against high spring pressure. This is a great way to reduce the friction, but can cause problems when the rocker arm has a higher range of motion due to the higher lift camshaft (opening the valve further). The factory trunion needle bearings can actually escape the trunion itself which can result in small, hardened pieces of metal being lost inside the engine. This is obviously very bad, and can have catastrophic results.

(Stock Rocker and Trunion)

This issue can be solved by installing a trunion upgrade into the factory rocker arms. This involves pressing out the factory trunion from the rocker and installing either a needle bearing unit designed to accommodate the high lift, or a brass bushing design which accomplishes the same goal, but with bushings rather than needle bearings. One common kit for this that I use is the CHE trunion kit. It uses brass bushings that have special oiling grooves in the bushings to provide oil to the spots that need it the most, and reduce as much friction as possible. The massive benefit is there are no small parts that could ever become dislodged and scattered throughout the engine.     

(Stock Rocker with CHE trunion kit installed)

 

1 comment

  • Good article! Clear, informative, and well written.

    Darrel Pritchard

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