The Art of Crankshaft Balancing: A Comprehensive Guide

Crankshaft balancing is a critical process in engine building, ensuring that the rotating assembly of the engine operates smoothly and efficiently. The primary goal of crankshaft balancing is to minimize vibrations and ensure that the engine runs as smoothly as possible. This process involves measuring, adding, or removing weight from the crankshaft to achieve a balanced state.

Understanding Bobweights

One critical aspect of crankshaft balancing is determining the bobweights, which consist of the rotating and reciprocating weights connected to the crankshaft. These weights are measured and entered into the balancer’s input screen to ensure accurate balancing.

Component Typical Weight Range
Connecting Rod 500-800 grams
Piston 300-500 grams
Wrist Pin 50-100 grams
Crankpin 200-400 grams

To measure the connecting rod weight, a scale and a special fixture are used to suspend the other end, ensuring that the rod is parallel and the small end is suspended. This method provides an accurate measurement of the rod’s weight, which is then entered into the balancer’s input screen.

Achieving the Ideal Balance

crankshaft balancing

When it comes to the acceptable balance for a rotating assembly, engine builders have varying opinions. However, a zero balance, meaning within 1 gram plus or minus, is often considered acceptable for performance engines. This level of balance ensures that the engine runs smoothly and efficiently, minimizing vibrations and reducing the risk of failure.

To achieve this level of balance, the crankshaft is placed on a dynamic balancer, which measures the vibrations and imbalances in the rotating assembly. The balancer then calculates the necessary weight adjustments, which can be made by adding or removing material from the crankshaft counterweights.

Precision in Crankshaft Balancing

Crankshaft balancing is a highly technical process that requires precise measurements and calculations. For instance, in a dual-plane dynamic crankshaft balancer build, data samples are taken within 1 degree of crankshaft rotation at a maximum of 1000 RPM. This level of precision ensures that the balancing process is as accurate as possible, resulting in a smoother and more efficient engine.

The balancer’s software uses advanced algorithms to analyze the vibration data and determine the optimal weight distribution. This process may involve multiple iterations, with the crankshaft being rebalanced until the desired level of balance is achieved.

Factors Affecting Crankshaft Balance

Several factors can influence the crankshaft balance, including:

  1. Crankshaft Design: The shape, size, and material of the crankshaft can affect its balance characteristics.
  2. Engine Configuration: The number of cylinders, firing order, and engine layout can all impact the crankshaft balance.
  3. Bearing Clearances: Proper bearing clearances are essential for maintaining a balanced crankshaft.
  4. Rotating Assembly Tolerances: Variations in the weights and dimensions of the rotating components can affect the overall balance.

To ensure optimal crankshaft balance, it’s crucial to carefully consider these factors and make adjustments as necessary.

Verifying Crankshaft Balance

After the crankshaft balancing process is complete, it’s essential to verify the results. This can be done by running the engine on a dynamometer and monitoring the vibration levels. If the engine runs smoothly and the vibrations are within acceptable limits, the crankshaft balancing has been successful.

In some cases, further fine-tuning may be required to achieve the desired level of balance. This may involve additional weight adjustments or even modifications to the crankshaft design.


Crankshaft balancing is a critical process in engine building that requires a deep understanding of the rotating assembly and precise measurement techniques. By determining the bobweights, achieving a zero balance, and ensuring the highest level of precision, engine builders can minimize vibrations and ensure that the engine runs smoothly and efficiently.

Crankshaft Balancing: The Basics
Crankshaft Balancing: Factors to Consider
Crankshaft Balancing: Advanced Techniques