Harley goes water-cooled! Jun10


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Harley goes water-cooled!

Harley-Davidson® is on the verge of switching to liquid-cooling for at least some of its traditional V-twin models. But die-hards needn’t throw up their hands in horror, as the Milwaukee firm’s take on water-cooled engines isn’t quite the same as other manufacturers. This is no all-new motor but a subtle update on the age-old pushrod V-twin gaining water-cooled cylinder heads that, on the outside, are indistinguishable from the old air-cooled versions.

The firm’s new designs have been revealed in a patent application that clear shows how the system works. Rather than charging headlong into an age of smooth-sided, water-cooled motors and the enormous radiators that accompany them, the Harley idea is to just apply a small element of water-cooling to the most sensitive area of the existing engines – in the cylinder head, and particular around the exhaust valve.

The patents show how a mildly redesigned head features a very simple water channel, basically a tube that enters the head on one side, loops around the exhaust valve and exits again. It’s not much, but allied to a pair of small radiators it should provide massive improvements to the firm’s abilityto keep the area around the exhaust valves cool.

Easy On Electra Glides

The patents show the system fitted to an Electra Glide style bike, with the radiators hidden in a stock-looking lower air deflector. Quite how they’ll be disguised in a more naked bike has yet to be seen, but the firm has added a large dose of flexibility to the system. By using two small radiators, each with an electric cooling fan and relatively little work to do, it can place the rads just about anywhere. The lowerhalf of the engine is unchanged, and even the heads look identical from the outside, with the exception of a couple of small-bore pipes taking water to and from them.

To keep mechanical alterations to a minimum, the design uses an electric waterpump, mounted in a unit that also includes a thermostat. On the design pictures, it’s again in front of the engine, mounted low down between the frame rails, but again the unit could be moved elsewhere if necessary – important not only for the firm’s wide range of different models, which all share similar engines, but also for the massive customising scene that’s grown around Harley-Davidson®. The flexibility of the cooling system means it can be repositioned relatively easily.

XR1200 uses oil cooling

Harley isn’t new to the idea that it needs to cool its cylinder heads more efficiently. The firm already uses oilcooled cylinder heads on the XR1200 with a similarly simple set-up, looping the cooling channels around the exhaust valves before taking the oil away to an external cooler. By taking the same idea but using water instead of oil, the firm can get even more efficient cooling without the need to disturb the existing oilsystem. And, of course, the V-Rod is completely water- cooled.

The cooling of the exhaust valves is particularly important. All the heat generated in the combustion chamber tries to escepe along with the exhaust gasses, straight past the exhaust valves and through the exhaust tracts, making them the hottest components in the entire engine. Modern engines run leaner than their forebears in an attempt to improve efficiency and reduce emissions – basically there’s more air and less peirol in the mixture they burn – and that actually increases the heat inside the combustion chamber.