I just found out that if you using March Performance pulleys or any other type of underive pulley you must bolt your stock crank pulley to the outside of the new crank pulley. It balances your motor. If you do not do this it will lead to internal engine damage

 

true.. the underdrive pulley isnt a balancer.. the stock pulley is the harmonic balancer.

 

Not true in ALL cases, as there are dampers that have the pulley built in, and then there are piggyback types that don't..
Many people using the piggyback type aren't aware that they also must use the stock damper..
I have an older March UD damper that I like, [not a piggyback] they don't make it any more though [not sure why not..]