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What Does Internal Balance vs External Balance Mean?
One of the most common questions customers ask when selecting a flywheel, flexplate, harmonic balancer, or rotating assembly is whether their engine is internally balanced or externally balanced. Using the wrong balancing components can cause severe engine vibration and potential engine damage.
What Is Engine Balance?
Engine balance refers to how the rotating assembly is balanced during the manufacturing process.
The rotating assembly consists of:
- Crankshaft
- Connecting rods
- Pistons
- Rings
- Rod bearings
- Harmonic balancer
- Flywheel or flexplate
A properly balanced engine operates smoothly and reduces stress on internal components.
What Is Internal Balance?
An internally balanced engine carries all of its balancing weight within the rotating assembly itself.
Internally balanced engines use:
- Neutral balance harmonic balancer
- Neutral balance flywheel
- Neutral balance flexplate
Advantages Of Internal Balance
- Reduced vibration
- Increased high-RPM stability
- Improved durability
- Greater flexibility when selecting flywheels and flexplates
Common BluePrint Examples
Many BluePrint:
- 427 SBC engines
- Pro Series SBC engines
- Pro Series BBC engines
- LS engines
are internally balanced.
Always verify the specifications for your exact engine.
What Is External Balance?
An externally balanced engine requires additional balancing weight located outside of the rotating assembly.
This weight is added to:
- Harmonic balancer
- Flywheel
- Flexplate
Why Is External Balance Used?
External balance is commonly used when crankshaft design limitations prevent all balancing weight from being carried internally.
Common External Balance Applications
Examples often include:
- 383 SBC combinations
- 400 SBC combinations
- Certain Ford 302 applications
- Certain Ford 351W applications
Always verify the specifications for your exact engine.
What Happens If I Use The Wrong Parts?
Using the wrong balance components may cause:
- Severe engine vibration
- Bearing damage
- Crankshaft damage
- Premature engine wear
- Component failure
Never assume a flywheel, flexplate, or harmonic balancer is correct without verifying balance requirements.
How Do I Tell If My Engine Is Internally Balanced?
Common indicators include:
- Neutral balance flywheel
- Neutral balance flexplate
- Neutral balance harmonic balancer
Many BluePrint engine specification sheets identify whether the engine is internally or externally balanced.
How Do I Tell If My Engine Is Externally Balanced?
Common indicators include:
- Visible balance weight on flywheel
- Visible balance weight on flexplate
- Weighted harmonic balancer
These weights are intentionally placed to complete the balancing process.
Flywheel And Flexplate Selection
When selecting a flywheel or flexplate, always match:
- Engine balance type
- Rear main seal style
- Crankshaft flange pattern
- Transmission application
Balance style is one of the most important factors when selecting drivetrain components.
Frequently Asked Questions
Is Internal Balance Better Than External Balance?
Neither is inherently better. Both systems work well when the correct components are used.
Can I Convert An Externally Balanced Engine To Internal Balance?
In some applications, yes. This typically requires rotating assembly changes and should be planned during engine building.
How Do I Know Which Flywheel I Need?
Determine whether your engine is internally or externally balanced before selecting a flywheel or flexplate.
Will The Wrong Flywheel Cause A Vibration?
Yes. An incorrect flywheel or flexplate is one of the most common causes of engine vibration.