V12 engines are typically found in high-performance cars rather than motorcycles. These custom motorcycles are often one-of-a-kind creations and not readily available for purchase.
It's important to note that the reliability of such custom-built motorcycles can vary depending on the expertise and quality of craftsmanship involved in their construction. Additionally, maintaining and servicing a custom-built motorcycle with a unique engine configuration can present challenges due to the limited availability of specialized parts and expertise.
If you're specifically looking for a reliable motorcycle, it's generally recommended to consider models from reputable manufacturers known for their reliability and quality control processes. These manufacturers include companies like Honda, Yamaha, Kawasaki, Suzuki, BMW, and Ducati, among others. They offer a wide range of motorcycles with different engine configurations, including inline-four, V-twin, and inline-triple, which are known for their reliability and performance.