Oil-Cooled Evolution

"What is the benefit of the new Harley-Davidson Precision Oil Cooling system that comes standard on the 2009 and 2010 Harley-Davidson XR1200." "And can I retrofit it to my Harley-Davidson Evolution Sportster" asked one of our readers?

We thought this to be an insightful question and wanted to get to the bottom of the issue. So, we had our resident Harley-Davidson experts, Bill Miko and his partner Todd Wilson from the Motorcycle Radio Network, go to work on this for us.

The Block Head Boys Respond

Harley-Davidson's new Precision Oil Cooling-a term that is found in Harley's service manual, but not in public literature-is a technology that we believe will keep Harley-Davidson's air-cooled motorcycles from having to become fully liquid-cooled in the near future. Unfortunately, the XR1200's Precision Oil Cooling system cannot be retrofitted to any other bikes in H-D's lineup; the engine in the XR is a completely new animal in this respect. However, the technology is of great interest.

With the ever-tightening emissions standards, our beloved V-twin has been forced into very lean fuel mixtures, resulting in engine temperatures increasing to extreme levels for the internal components. Harley's Precision Oil Cooling puts cooled oil directly on components inside the engine, specifically where it is needed most, to dramatically drop internal engine temperatures. Oil jet assemblies in the flywheel compartment spray oil directly under the piston crown to help lower temperatures driven up by combustion heat. Additional oil flow is directed across the cylinder heads, as well as through passages in the exhaust valve and port, to cool those critical areas.

We believe that technology such as Precision Oil Cooling will keep the air-cooled V-twin in the Harley line up for the forseeable future, and Miko strongly believes that the system will soon be utilized on other models in some form-including the Big Twin engines.

Sadly, air-cooled engines are also at risk from sound regulation, which measures the total volume that the motorcycle emits, not just the exhaust noise. A significant portion of sound is created by air simply passing over the cooling fins on the cylinders. The battle to extend the life of the classic air-cooled motorcycle powerplant continues.