i'm in the process of rebuilding my 13bt. Looks like one rotor has a piece that chipped off of the apex seal groove, like the corner of the rotor and bit into the face of the rotor, so i've decided to replace it

I have the option of replacing both rotors, or just one. So my main question is:

If i get another "D" weight rotor, will I need it balanced with my other rotor and rotating assembly?

and when you get your rotating assembly balanced, what components do they balance? (front counterweight, rear counterweight, eccentric shaft, rotors?)

I've been doing some researching on here, and i've heard that balancing is not needed unless you're making a high-revving motor, but most of mine is just going to be used on the street.

 

you will be fine as long as you stay in the same class. I believe though the JDM parts can vary greatly to USDM rotors though, even though they are the same letter. Keep the weight difference under 25g (make sure both have bearing or no bearing when weighing)....