Tech Tips on Installing a Harmonic Balancer on a 350 Chevy

by John Stevens J.D.

Each time one of the 350's spark plugs ignite the air/fuel mixture within its cylinder, the resulting explosion sends a tremendous vibration through the piston, connecting rod and finally to the crankshaft. Left unchecked, these vibrations would quickly destroy the engine. The sole purpose of the 350's harmonic balancer is to absorb this vibration. Unfortunately, the balancer's effectiveness diminishes over time and must be replaced. Removing the balancer is usually considered to be more difficult than installing it, but failing to properly install the balancer can be even more destructive than running the engine with an old one.

Aligning the "Key" and the "Keyhole"

The harmonic balancer slides onto the tip of the crankshaft. To prevent the balancer from rotating independently of the crankshaft when the engine is running, a small vertical piece of metal, called a "key," is used at the tip of the 350's crankshaft. The circle located in the center of the harmonic balancer slides over the end of the crankshaft. Within this circle is a small cutout, called a "keyhole." The key and the keyhole must be aligned to properly install the harmonic balancer. Slide the harmonic balancer onto the end of the crankshaft, then twist the balancer until its keyhole aligns with the crankshaft's key.

Installing the Harmonic Balancer

The harmonic balancer attaches to the end of the crankshaft with a single bolt. A washer is also used to ensure that the force of the bolt is evenly distributed through the balancer to the crankshaft. Slide the bolt through the washer, then insert the bolt through the center of the balancer. Hand tighten the bolt into the crankshaft. The final step to installing the harmonic balancer is the one that is most often overlooked. The bolt is commonly tightened until it cannot be tightened anymore. Proper installation requires that the 350's harmonic balancer's bolt be tightened to only 60 pound-feet of torque to avoid damaging the balancer, the crankshaft, or both. Therefore, only a torque wrench should be used to tighten the bolt to the proper torque setting.

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