How to Properly Shim an RC Electric Motor

How to Properly Replace and Shim an RC Electric Motor

Your RC motor works hard.

Whether you're racing, bashing, crawling, or speed running, the motor bearings are subjected to:

  • high RPM
  • heat
  • vibration
  • impacts
  • side loading

Over time, motor bearings wear and develop excessive play, causing:

  • noise
  • vibration
  • reduced efficiency
  • loss of power
  • premature motor failure

At FastEddy Bearings, we often hear customers ask:

"Should I shim my motor when replacing the bearings?"

The answer is absolutely yes—if necessary.

Properly replacing and shimming your RC motor bearings can dramatically improve:

  • smoothness
  • efficiency
  • bearing life
  • motor performance

Let's walk through the process.

Signs Your Motor Bearings Need Replacement

Common symptoms include:

  • squealing noises
  • rough spinning
  • excessive shaft play
  • vibration
  • overheating
  • reduced runtime
  • inconsistent performance

If your motor sounds like a coffee grinder, it's probably time for new FastEddy Bearings.

What Is Motor Shimming?

Shimming is the process of removing excess movement from the motor shaft.

Most electric RC motors have:

  • a front bearing
  • a rear bearing
  • a rotor shaft running through both

Manufacturing tolerances can sometimes leave:

  • excessive endplay
  • excessive shaft movement

Proper shimming helps keep the rotor centered and stable.

Why Shimming Matters

Excessive shaft movement can cause:

  • premature bearing wear
  • inconsistent rotor alignment
  • vibration
  • efficiency loss
  • stator contact in severe cases

Properly shimmed FastEddy Bearings help maintain precise rotor positioning.

Tools You'll Need

Before starting, gather:

  • hex drivers
  • bearing puller
  • shim assortment
  • calipers (optional)
  • replacement FastEddy Bearings
  • bearing press tools
  • clean workspace

Step 1: Remove the Motor From the Vehicle

Disconnect:

  • battery
  • ESC wires
  • motor mounting screws

Remove the motor from the chassis.

Before disassembly, inspect:

  • pinion gear
  • motor mount
  • gear mesh

This is a good time to clean accumulated dirt and debris.

Step 2: Remove the Endbell

Carefully remove:

  • rear screws
  • endbell assembly

Slide the rotor out slowly.

Important: Strong magnets can pull the rotor aggressively. Take your time to avoid damaging:

  • windings
  • sensors
  • rotor shaft

Step 3: Remove the Old Bearings

Motor bearings are typically press fit.

Use:

  • bearing pullers
  • sockets
  • bearing drivers

Avoid:

  • hammering
  • prying
  • excessive force

FastEddy Bearings recommends supporting the housing properly during removal.

Step 4: Inspect the Motor

Before installing new bearings inspect:

  • rotor shaft
  • bearing pockets
  • endbell
  • motor can

Look for:

  • wear
  • scoring
  • bent shafts
  • excessive heat discoloration

A damaged shaft can quickly destroy new bearings.

Step 5: Install New FastEddy Bearings

Install the replacement bearings carefully.

Always apply pressure to the outer race only. Never press on:

  • the inner race
  • the seal

Improper installation can damage a new bearing before it ever runs.

FastEddy Bearings should install smoothly with even pressure.

Step 6: Check Rotor Endplay

After reassembly, check for shaft movement.

Push and pull the shaft gently.

You may notice:

  • very little movement (ideal)
  • excessive movement (needs shimming)

Most RC motors benefit from .005"–.015" of endplay. You want slight movement—not zero movement.

Step 7: Add Shims If Needed

Motor shims are typically installed behind the front bearing or between the bearing and rotor, depending on motor design.

Add shims gradually. Common shim thicknesses include:

  • 0.1mm
  • 0.2mm
  • 0.3mm

Install one shim at a time and recheck shaft movement.

Avoid Over-Shimming

This is one of the most common mistakes.

Too much shim can:

  • preload the bearings
  • create drag
  • generate heat
  • shorten bearing life

The rotor should spin freely. FastEddy Bearings recommends eliminating excessive play without creating preload.

Step 8: Reassemble the Motor

Once properly shimmed:

  • reinstall the rotor
  • reinstall the endbell
  • tighten screws evenly

Spin the shaft by hand. The motor should feel:

  • smooth
  • free
  • quiet

Step 9: Check Gear Mesh

After reinstalling the motor, check:

  • pinion alignment
  • spur gear alignment
  • gear mesh

Improper mesh can quickly destroy both bearings and gears. A properly shimmed motor deserves properly adjusted gear mesh.

Common Shimming Mistakes

Zero Endplay

No movement may sound good but often creates bearing preload. A small amount of movement is necessary.

Too Many Shims

Excessive shimming can:

  • increase temperatures
  • increase drag
  • shorten bearing life

Ignoring Bent Shafts

A bent rotor shaft will destroy new bearings regardless of how well they're shimmed. Always inspect before reassembly.

Cheap Bearings

Low-quality bearings often develop play quickly. FastEddy Bearings are designed to provide smooth operation and long service life in demanding RC applications.

Benefits of Properly Shimmed Motors

Correctly shimmed motors typically provide:

  • smoother operation
  • reduced vibration
  • improved efficiency
  • longer bearing life
  • better power delivery
  • lower operating temperatures

Many racers consider motor shimming one of the easiest performance improvements available.

Why Choose FastEddy Bearings?

FastEddy Bearings has been helping RC enthusiasts for over 20 years.

FastEddy Bearings motor bearing replacements are trusted by:

  • racers
  • bashers
  • crawlers
  • speed runners
  • hobbyists worldwide

Because when it comes to electric motor performance, precision matters.

Final Thoughts

Replacing worn motor bearings is one of the best maintenance upgrades you can perform.

When combined with proper shimming, new FastEddy Bearings can help restore:

  • smoothness
  • efficiency
  • reliability
  • performance

A properly shimmed motor runs quieter, cooler, and more efficiently—and your bearings will thank you for it.

The next time you replace motor bearings, take a few extra minutes to check endplay and shim correctly. The results are well worth the effort.

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