Answer :
Final answer:
The Crankshaft main bearing in a radial engine is least likely to be a roller or ball bearing.
Explanation:
The bearing that is least likely to be a roller or ball bearing out of the options given is the Crankshaft main bearing in a radial engine.
A roller or ball bearing is typically used in applications that require high-speed rotation and low friction, such as the rocker arm bearing in an overhead valve engine or the master rod bearing in a radial engine.
On the other hand, the crankshaft main bearing in a radial engine supports the main rotating shaft and is subject to high load and stresses, making a roller or ball bearing less suitable and a plain bearing or a journal bearing more commonly used.
