Whether you purchased an Atomik MM450 or the VMX450 e-gyro upgrade kit, there is a chance your flywheel may not be very well balanced. You might be able to get some idea of how well your flywheel is balanced by the sound it makes or by the vibration you feel holding the bike, but the only real way to know is to open the back wheel and see for yourself. I had a hunch my flywheel was not balanced because it had a ruff sound to it and some vibrations. Note the flywheel is reported to run at 12000 rpm so it will sound a bit loud like a turbine and the stock bearings seem to be very loud too, but at 12000rpm they should all have been balanced at the factory. Nonetheless, its a good thing to check for the next time you open your wheel up. If balance is really bad, bike is under warranty, and you dont have ability to balance then maybe Atomik can help out, otherwise read further.
Here are some videos showing unbalanced and balanced flywheels, taken by Chris at http://www.extremenitrohobbies.com.au/
One of the first things you’re going to face when dealing with the e-gyro and back wheel is that Atomik removed the plugs going from the gyro esc to the rear wheel motor. So I put my own 3.5mm bullet connectors somewhere near where the wires hide near the rear shock area out of the way. This allowed me to disconnect the gyro motor and not deal the whole motor and wires connected to the esc why I try getting things balanced. Not necessary though. The biggest concern for me was finding or making a stand that I could use to test balance of flywheel. Lucky for me I owned a Duratrax DX450 and the bike stand allowed me to sit the Atomik axle on it without the flywheel touching the ground! You may need to make something out of wood or maybe use a vise, not sure. What I did was take the whole axle, motor with its red hub, and the flywheel and rest it on the bike stand. I flipped direction of the flywheel so the magnets didnt interfere with motor and so flywheel could rotate freely. You could also buy a drill bit that is 12mm or 15/32 that fits the 12 ID of flywheel bearings and forget about using motor hub altogether, your choice. (UPDATE 2/28/13 – Added an image of the DuBro balancer sold for maybe $25 that Ive been told works great for balancing the MM450 flywheel if you want very accurate way to balance.)
Next clean the bearings with something like wd40 of all greese and dirt so they run as fast as possible. If your bearings are trashed, get new ones before attempting balancing so there is no interference. Once on the stand on a level table begin turning flywheel to different spots to see if it is heavy on one side. A balanced flywheel will come to rest at any spot and not want to rotate to a heavy side. Mine wasn’t balanced and had a heavy side, but never rested at an exact spot but about a half inch area so I had to decide on the two end points of the heavy side and marked the middle and drilled at that spot.
Once you have that spot marked you need to be EXTRA carefull with the metal shavings that come off from drilling. I used tape and before I got down to drilling, I masked off both sides to seal off entry from metal shavings getting in and sticking to those powerfull magnets on flywheel. That would be a nightmare to deal with. I clamped my flywheel down on a nice flat surface and took a smal drill bit to make a dent so the bigger drill bit I was going to use would not wonder off. How much you need to take out is up to you and depends on how bad yours is out of balance. Its better to be cautious and take a little bit out at a time and test balance, then it is to take too much out and have the opposite side need to be balanced to offset your mistake. You dont drill a hole all the way through either. Personally, I used a 15/32 drill bit, took my time, and once finished I had drilled down to a depth of about 1.8mm at the center. Just like that I had a balanced flywheel that would not want to rotate to any heavy side no matter where it was rotated. Something turned out right the first time, wow imagine that, I do luck out once in a while lol.