A harmonic balancer (also called a damper) absorbs the torsional vibrations generated by the crankshaft as it spins. Without one, those vibrations can cause timing inaccuracies, bearing wear, or even crankshaft failure over time.

By reducing this harmonic resonance, a balancer helps your engine run smoother and last longer — especially at higher RPMs.

Common signs of a failing balancer include:

• Visible cracks or separation between the rubber ring and the metal hub.
  
• Wobbling at idle (you can sometimes see the pulley moving off-center).
  
• Belt squeal or misalignment.
  
• Unusual vibration, especially at certain RPMs.
  

If you notice any of these, replace the balancer immediately — a failed unit can damage the crankshaft or front seal.

SFI 18.1 certification means the balancer meets strict safety standards for high-RPM and racing use.

For street engines under 6,500 RPM, a standard performance balancer is usually fine.

For racing, boosted, or high-RPM builds, you should absolutely use an SFI 18.1-certified damper. It’s not just safer — it’s often required for competition.

• Internal balance: All counterweighting is handled internally by the crankshaft. The harmonic balancer and flywheel are neutral (no external weights).
  
• External balance: Some of the engine’s counterweighting is handled by the balancer and/or flywheel, which have offset weights.
  

Always match your balancer to your engine’s balance type — for example, small-block Chevys can be either, but LS engines are all internally balanced.

• Elastomer (rubber) dampers: Great for most street and mild performance builds. Affordable and reliable.
  
• Fluid (viscous) dampers: Use internal silicone fluid to absorb vibrations across a wider RPM range. Better for high-RPM, high-power, or racing engines.
  

In short — elastomer for everyday performance, fluid for extreme builds.

It’s best not to reuse the old bolt. Many factory and aftermarket crank bolts are torque-to-yield, meaning they stretch slightly when torqued.

Always use a new, high-quality bolt when installing a new balancer to ensure proper clamping force and safety.

If you’re replacing your balancer with a direct-fit OEM replacement or neutral-balanced unit, no rebalance is needed.

However, if you switch from external to internal balance, or if the new balancer’s weight differs, you must have the rotating assembly rebalanced by a machine shop.

• Use a balancer installation tool — don’t hammer it on.
  
• Lightly lubricate the crank snout and keyway.
  
• Torque the crank bolt to spec (consult your engine’s service manual).
  
• Verify alignment with timing marks and pulleys.
  
• Check that the outer ring is fully seated and doesn’t wobble when running.
  

For LS engines, it’s also smart to check crank bolt stretch if you’re using OEM hardware.

Replace your balancer if:

• You’re rebuilding your engine or upgrading to a performance crank.
  
• The outer ring has separated or the rubber has hardened.
  
• The timing marks no longer align correctly.
  
• You experience vibration or belt issues that point to imbalance.
  

It’s inexpensive insurance against serious engine damage — especially on older or high-mileage builds.

Stick with the stock diameter unless your setup requires otherwise.

• Smaller (underdrive) balancers reduce parasitic drag and slightly free up power, but can slow accessories.
  
• Larger balancers help with torsional control in high-RPM or boosted setups.