Regulator Rectifier Questions

Motorcycles have AC and DC charging systems:  Almost all modern motorcycles are equipped with a three-phase AC (Alternating Current) generator, while the electrical system on the bike is a DC (Direct Current) system. The rectifier part inside the regulator-rectifier converts the AC-current to the DC-current the battery needs. There are three diodes(phases) within the rectifier that allow current to go in one direction through the device (ie. Stator > Rectifier > Battery). But will not allow currrent to flow in the opposite direction

A motorcycle start with a non-functioning Rectifier: The rectifier is part of the charging system. If you put a freshly charged battery in your motorcycle and you have a bad regulator rectifier, it won't stop your motorcycle from starting, but your battery won't stay charged and eventually will not start or stop running. The regulator rectifier on your motorcycle performs two functions.

Bad or Dirty terminals Connectors and Damage the stator and Regulator Rectifier 

No Spark: A bad regulator rectifier will not typically cause no spark directly, but it is generally recommended to replace your ignition coils and regulator rectifier before installing a new ignition unit. 

Regulator Rectifiers do run hot!  It's normal for an OE#  shunt-type regulator rectifier  to get quite hot — especially when the load being drawn by the electrical system is low.The Regulator Rectifier (RR) simply converts excess stator output wattage (that isn't needed to run the bike and charge the battery) to heat. That's why there are cooling fins on the RR

R\Rs  change voltage:  Although a rectifier converts alternating current to direct current, the resulting direct current isn't a steady voltage.