August 2004


I bought an E20R motor in excellent condition.

Unfortunately when I tested it at home it ran worse than an E15R on 12Volts!

The armature spun freely so it was not binding.


I had often heard guys at the club talking about balancing your armature to get 

more power and smoother running out of your E15R and E20R motors.

I decided to give it a try.


The idea behind balancing the armature is simple. You balance the armature on a 

balancing device and the heavy side will roll down to the bottom.

You grind away the metal on the heavy side/s until the armature is balanced.


Remove the brushes and brush springs by unscrewing the retaining caps.

Loosen the 4 nuts and pull off the right hand side plate as it does not have the 

brush mounts on it. Next remove the armature.


My first balancing machine. There was way too much friction and it just did not 

work consistently.


This solution worked just fine. The heavy side consistently rolled down to the bottom.


I used a round, diamond coated grinding bit to grind away metal on the heavy sides.

I had to grind a fairly deep and wide hole before I noticed a change on the balancing



I had to grind metal off of two of the lobes to get the armature balanced.

If I roll the armature on the balancing machine, it stops in different positions now. 


Once the armature was balanced I polished the commutator and put the engine back

together and tested it.

To my disappointment there was not much difference in performance. It still lacked power.

I tried increasing the brush pressure on the commutator by stuffing small wads of paper behind

the springs.


This made a huge difference and the motor runs smoothly, quietly and with plenty of power.


Placing paper wads behind the springs to increase brush pressure on the commutator.


It almost looks like a close up of a Formula 1 car's brake disk under heavy braking!




Was it worth it?

Quite honestly I don't think so. 


- After all that effort it seems like the spring pressure was the main problem.

- This E20R still does not run with the same power as my other unmodified E20R's. 

- This motor is now not a (Pristine) unmodified collectors item.