Some of you may have already seen this thread on the other board, was hoping to flesh it out a bit before bringing it over here, I think it's ready. Upon hearing an Indian Scout run for the first time a lot of people will ask "what is that high pitched whining noise?". It was one of the first questions I had when I first started looking into the bike and initially I found it kind of off-putting, then I started reading into it and learned that it's one of the many things that has made a Scout a Scout since 1920. The more I read about it the more it became a reassuring sound to me, a sound that brings a number of advantages along with it. This thread is an effort to clear up some of the mystery behind the characteristic whine of the Scout to those who are still confused and an effort from me to fill some of the gaps in my own knowledge of the design. That being said, I'm learning all of this for the first time and I'm counting on those of you with more skin in the game to point out when and where I am wrong about any of this. So let's start at the beginning, the 1920 Indian Scout: To make the Indian Scout as compact as possible, Charles B. Franklin utilized a semi-unit-construction technique in which the transmission was bolted directly to the engine, connected by primary gears rather than a primary chain drive, as used on rival motorcycles. This stiff and compact packaging made the Indian Scout one of the finest handling motorcycles ever made up until that point. According to Allan Girdler's The Harley-Davidson and Indian Wars, the Indian Scout was the 1st American V-twin motorcycle to use a gear driven primary. For comparison, here is a 1920 Harley-Davidson Model "F": Note the difference in primary size and construction. It seems to me that, at the time, the geared primary drive was the most significant innovation in Indian's lineup. It gave the Indian Scout three significant advantages over the competition: weight reduction (making it faster), rigidity (making it more nimble), and increased reliability (due to a gear driven primary requiring no adjustment or maintenance). Even on the 1920s Indian Scouts you can hear the same characteristic gear whine, though it is a bit harder to pick out beneath the much louder exhaust and valve noise. Here is a 1929 Indian Scout 101. You can hear the geared primary most clearly during old Johnny's take-off around 1 minute 50 seconds and during his return at 2 minutes 9 seconds. In 1934, Indian further improved the rigidity, handling, and lightness of the Scout by incorporating the Keystone frame into the Scout Sport model, a two piece frame that bolted together at the top and to engine at the bottom, using the engine as a stress member. In addition, removing down tubes from the frame design significantly improved cornering speeds and lean angle by increasing ground clearance beneath the bike. However, two years earlier in 1932, the financial pressure of the Great Depression led Indian to cut costs by switching to a chain driven primary design. The whistling geared primary, the multi-piece frame joined at the top and bolted to the engine at the bottom, the pursuit of speed through weight savings, maneuverability, and cornering clearance rather than bore size. It's all there in this new generation of Scouts, nods to the Scouts of the past and continuing the tradition of breaking tradition by shamelessly flaunting a humbly sized liquid cooled DOHC V-twin free of fake cooling fins, hiding the rear shocks and swing arm in plain sight, and happily tossing out the notion that a cruiser can't be revved to 8000 RPM day after day without breaking a sweat. Like the original generation of Scouts, the new Scouts are a celebration of innovation and competition. Here is a look at what is going on inside the heart of the modern Scout. The middle row shows both the left side and right side view of the engine, the bottom row shows one side flipped and overlayed on top of the other to provide a translucent view of the entire bottom end, an easier way to see how and where each gear set meshes with the next. The death of the gear driven primary design appears to have occurred in 1932. And the resurrection of the geared primary in V-twin cruisers, as far as I can tell, occurred in 1981 when Yamaha built the first transverse Japanese V-twin cruiser: 1981 - 2007 Yamaha Virago: Anybody here know of any other V-twin cruisers using a geared primary between 1932 and 1981?