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This page identifies and demonstrates the more important aspects of preparing C Can motors. Most of the operations described may be undertaken with simple tools and ensure that you finish up with a very competitive and reliable racing motor. The article is written around the new RJR C can motor, but most aspects apply to all motors of this type.
The article also gives you an idea of what you get if you decide to purchase a pre-conditioned motor from AB Slotsport, because this is what we do before you get it!
Pre-conditioning is a kind of “blueprinting” without the frills which ensures a quick and efficient motor.

Step 1 ;- Take the motor out of the packet, lightly lubricate the bearings and run on a power supply at 5 volts for approx. 15 minutes.
Step 2 ;- Strip the motor. Leave the original armature spacers in place
Step 3 ;- inspect the brush springs and ensure they are set at identical angles, 90 dgerees is about standard, you can increase this angle to achieve more brakes, but remember higher brush spring tension means more brush wear and probably less revs. Test fit springs on the spring posts and ensure the short arm of the spring does not fowl the brush hardware.

Step 4 ;- It’s time to check magnet alignment. With the RJR motor it is an idea to move the magnets forward slightly in the can. This also dispeneses with the need for additional armature spacers at the endbell end of the motor. Slide a 3/32” axle through the Comm Vents as shown and lightly tap the magnets down the can using a plastic drift or screwdriver handle. The axle should float freely side to side in the Com vents. Your magnets are now in line. Using a thin Super Glue, apply a little to the back of the magnet and let it run behind it, locking it firmly in place.
Step 5 ;- Remove the plain oilite bearing from the can with a gentle tap and carefully enlarge the hole sufficiently to fit the ballrace. Ensure the ballrace will slide easily into the hole. Slide a very thin armature spacer (3 - 5thou) on to the end of the armature shaft, followed by the ballrace. Assemble armature in can and fit endbell. Hold the motor can end up, apply flux around the ballrace. Let the ballrace “settle”, so there is no endfloat in the assembly and solder in position. Strip the motor. Wash all traces of flux from the bearing area. Re-assemble the can and endbell this time with a 0.535” diamond hone in place and run this through the magnet, this will ensure a constant and optimum bore for the armature to run in.

Step 6;- Next up is the slightly more technical bit. After removing any dust or gunk from the can and magnets, the magnets are zapped in the can to ensure maximum magnetic flux.
The commutator is diamond trued (just a skim to ensure it is completely “round”).
The Com is then polished using an SPR com polishing stick. This removes any sharp edges in the segments and minimalises brush wear and arking. (these sticks can also be cut down to brush size and used to polish the coms in “sealed motors “ such as 16d’s etc.

On most motors this is when a Diamond faced brush hood tool gets used, however, RJR are one of the rare manufacturers that do this at the factory, so usually there is no need. Just ensure that the brushes slide easily in the brush hoods. Re-assemble the motor leaving out the thin spacer you put on the shaft before fitting the ballrace. You should now have perfect end float if you allowed the ballrace to “settle” correctly.
Step 7 ;- Now comes the time that lots of folk hate - Shunting the brushes. This ensures good electrical contact with the brushes and is essential for good performance. As a rule C can motors don’t pull a vast amount of current so it is not necessary to use massive diameter shunt wire. Most shunt wire nowadays is know as “jump rope”, that is 3 main bundles of wires platted together. Unplat the 3 bundles and just use one. This is quite sufficient for it’s purpose and what’s more it won’t “hold back” the motor brush as it wears down.
Using a small file, open the vertical slot in the brush as shown, fit the brush into the hardware and attach shunt wire and spring.

When fitting shunts, ensure there is enough slack in the shunt wire to allow trhe brush to move down the brush barrel in the hardware as it wears. Also make sure when you solder the shunt to the hardware terminals that solder does not creep down the shunt wire and turn it rigid. This will stop the shunt flexing and will cause a motor failure in a very short run time. After you have soldered the shunts, go back a step and check that the shunt still has good flex. If not take it off and start again! Insufficient brush contact with the Com caused by “hung” brushes is responsible for much irreversible motor damage, leading to overheating and total Com destruction, where the com gets so hot it delaminates and fails.

Finally once the shunts are on, check that the motor turns freely, lubricate bearings and set it to run once again at 5volts. Run for approx 10 minutes. Never overlubricate the endbell bearing! Oil kills more brushes and motors than anything else!
In our shop, once the motor is run in we check it once more with the digital rev counter and generally we see a noticable improvement in performance. One last thing, NEVER overrev your motor on a power supply, it proves little and with the peak performance of many modern motors, free running at high voltage can lead to total destruction of the Com.