Warm Up Times of Radial Engines.

[Crumpp]

The purpose for warming an engine is to get the oil warm so that the bearing surfaces are lubricated properly.

True but even more important is the fact aircraft engines have what is called a "choke grind" cylinder.

That means the cylinder is wider at the base and narrower at the head when cold. When warmed up, the head is hotter than the base so it expands and the cylinder walls become straight.

If you operate your engine without it being warm, then you are really putting excessive wear on the head, pistons, and rings.