is putting a motor on a bike illegal

The legality of putting a motor on a bike depends on various factors including the laws and regulations of the specific jurisdiction where you are riding the bike, the type of motor, and how it is being used. In many places, it is legal to install a motor on a bicycle, but there may be restrictions on the type of motor, its power output, and whether it meets certain safety standards. 

Some jurisdictions may require registration, licensing, or insurance for motorized bicycles, and there may be specific rules governing where and how they can be operated. Additionally, modifying a bicycle with a motor may affect its classification, potentially requiring it to meet certain vehicle safety standards.

It’s important to familiarize yourself with the laws and regulations in your area before installing a motor on a bicycle to ensure that you are in compliance with the law.