ASK KEVIN: Why Does Harley Use a Cam Chain in the Twin Cam 103?

Harley-Davidson Twin Cam 103 engine

QUESTION: Why does Harley-Davidson insist on using a cam chain in the Twin Cam 103? With all the problems HD has had with jammed oil pumps, one would think they would have moved to geared cams, as in the Evo engine. Is there any advantage to a cam chain? I would buy an Ultra Glide if it would last as long as my Gold Wing (or Yamaha V Star for that matter). Seriously, would you buy a car that needed a rebuild at 70,000 miles?

Marshall M. Miller

ANSWER: I have not heard The Voice enunciate this from atop Mount Olympus, but I'd hazard a guess the chain solves a potential noise problem with gears. Back in the 1980s, when The Motor Company was "killing the noise to keep the music," part of noise abatement was three or four really expensive Swiss-made gear grinders, whose job was to generate really accurate tooth profiles that were quieter than gears that had just been shoved through a hobbing machine. Because cams kick back when a spring goes over the nose, there will be an audible "click" every time it happens, unless tooth-to-tooth clearance is reduced to a practical minimum. Beyond that, you could go to spring-loaded "scissors" gears as Honda has done on occasion, as a means of taking up noise-making tooth-to-tooth clearance.

I love gears. Just the idea of such precisely made forms in hard steel is very appealing. Pure racing engines almost always have gear-driven cams because of the durability of their timing accuracy. And I frankly like gear noise. We used to listen to the Superbikes at Laguna in the 1990s, trying to see which ones had the "kit" geared cam drives. And the phasing gears on the Suzuki 500 GP bikes made their own special sound.

But Harley is up against it. The no-muffler people give them a bad rep to overcome, so The Motor Company works hard to suppress things such as gear noise, panel vibration, piston noise, etc., so they can legally generate the romantic rumble that sells so many units for them.

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