Which bearing is least likely to be a roller or ball bearing?

The master rod bearing in a radial engine is least likely to be a roller or ball bearing due to its specific design and function. In radial engines, the master rod is an essential component that directly connects to the crankshaft and transmits the forces generated during combustion.

These bearings are typically designed to handle high loads and provide a robust surface for rotational movement. The master rod bearing often uses a bushing type or plain bearing arrangement, which allows for a larger surface area to manage the wear and heat generated in high-stress environments. By employing a plain bearing design, these bearings can better absorb shock loads and manage the friction with sliding motion rather than rolling motion that roller or ball bearings provide.

Additionally, in radial engines specifically, the space constraints and the design location of the master rod bearing make it more practical and reliable to use this type of bearing rather than a rolling element bearing. This design choice is critical in ensuring the durability and longevity of the engine's operation under the unique stresses experienced by radial configurations.

In contrast, piston pin bearings, camshaft bearings, and main bearings may commonly use roller or ball bearings given their operating conditions and the need for efficient load handling and minimizing friction.