Harley-Davidson engines refrigerated by water: the twin-cooled system

We are going to deal with the theme of the new liquid cooling in the American bichilindrums: many years ago it was speculated with liquid cooling in Harley-Davidson's Big Twin engines and finally arrived during 2014, under the famous Rushmore project.
Its implementation responds more to emission control reasons (for this it is important to stabilize the engine temperature) whose regulations are increasing as faithful as possible with respect to its origins.

Development history
An engine transforms chemical energy into mechanical energy, generating large amounts of heat during the process. For the proper functioning of the engine, this heat must be controlled in some way in order to avoid damage to the components. Traditionally, air cooling is used in HD engines, providing cylinders and butts (the motor parts where it is most heat) of large aluminum fins through which the air flows while circulating with the vehicle. This air passes "steals" heat to the engine, lowering its temperature.

It must be said that the liquid cooling implemented by Harley-Davidson differs from the traditional one, where the cylinders and butts are mounted inside some "wet shirts" through which the water circulates.

To preserve the traditional air cooling appearance an experienced concept is used a few years ago with the XR1200 models, where the butts were equipped with an internal oil circuit connected to an exterior radiator (precision cooling) that managed to reduce the operating temperature of the hottest parts around the exhaust valves.

"Invisible" solution
After successfully experiencing this system in sports models, Milwaukee's factory simply had to replace oil with water and almost had a liquid cooling system.
But not everything is as simple as it seems. As happened with the ABS braking system, the challenge was completely hiding the system so that it did not affect the classic motorcycle aesthetics.
The solution consists of dividing the water radiator into 2 parts, which are hidden into the lower fairies.

A mixture in equal parts of water and coolant, driven by a pressure pump located below the voltage regulator, in the front of the chassis, circulates inside them. If the case requires it, two fans mounted after each radiator will be activated.

The filling plug, which regulates the general pressure of the system, together with the expansion tank are located within the lower right fairing.
The system has a temperature sensor and a thermostat that cuts the passage of the refrigerant to the radiators when the engine is cold, thus reducing the time it takes to reach the operational temperature of the engine, it is then when the Step towards radiators to cool the circuit.

Models and applications
Together with the benefit that the temperature control provides to comply with the increasingly strict regulations there are other points where improvements are achieved thanks to the liquid cooling system.
One of them is that the sensation of heat from the engine has been reduced in a sensitive way for the driver, and together with the new location of the exhaust collectors, the comforter's comfort also improves.
The other advantage is that it has been possible to increase the compression of the cylinders, which have gone from 9.6 to 10: 1, therefore increasing the power of the propeller.

The present and the future
Currently, models with “Twin Cooling” liquid cooling, as the mucus calls it, are certain versions of the Touring range. However, it is very likely that the application will extend more to more models in the next years ...

Frank Burguera

#mecanicaharley