F4 Motor: Replace Brushes or Motor?

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• F4 Brushes
• F4 Motors

When to check

Check brushes every 6 months (750 hrs). Replace before 1500 hrs even if they still look okay.

How to check

Follow our F4 Brush Replacement Guide through the step that exposes the brush cavity. Don't disconnect or replace anything yet.

What to look at

Pull back the spring arm and look at the brush. Then look past it at the copper segmented ring it presses against.

• Even copper color across every segment
• Smooth surface, no grooves
• Life of motor less than 1,500 hours

• Dark or blue-black segments
• Grooves or pits worn into the copper
• Black carbon packed between segments

Replace the motor. New brushes won't fix a damaged ring, and you'll be back here again soon.

(Motors can be recycled.)

Break-in: after installing new brushes

Run the motor normally. Some sparking in the first several cycles is normal while the new brush wears in to match the ring. It should fade within a few minutes of run time. If it doesn't fade, see 'If you see sparking' below.

If you see sparking

A little sparking during that first open-bed run is normal; new brushes aren't fully seated yet. It should fade fast, within a few minutes.

If it doesn't fade, or it's heavy and steady:

• Stop and recheck the brush is seated all the way in the cavity, and the spring arm is back in its notch
• Look at the ring again for the damage signs above (dark segments, grooves, pitting)
• Ring clean, installed correctly, sparking still won't quit: that's not a seating issue, treat it as a bad motor.