1903 HD serial number 1

Broken strap

The timing belt at the rear is celebrating its 40th birthday at Harley-Davidson

The Sturgis was the first production Harley with a timing belt secondary drive
Since 1993, all Harleys have had timing belts instead of secondary chains
The advantages include low maintenance, long service life and cleanliness

(Neu-Isenburg, June 30, 2020) Belt drive - this is the name given to a simple and effective way of transmitting power between shafts. It is used to regulate the valve timing of engines, drive turntables and move industrial robots. The concept itself is ancient and came to its heyday in the era of industrialization.

At that time, a powerful central steam engine powered a large number of individual machines that were lined up next to each other in large factory halls via steel shafts on the ceilings as well as pulleys and transmission belts. Later, the idea with shafts, pulleys and mostly leather flat belts was also used elsewhere - for example in agriculture and mining.

The timing belt at the rear is celebrating its first birthday at Harley-Davidson — MY16 Key Features. Street XG750

The timing belt at the rear is celebrating its 2nd birthday at Harley-Davidson — MY16 Key Features. Street XG750

So it made sense motorcycles using this technology. The first bike, which bore the names of its creators Harley and Davidson on the tank, transmitted the power of its approximately 405 cubic centimeter single-cylinder to the rear wheel via a leather strap. This worked quite well when the engines' power and torque were still limited. But with the introduction of the first Harley-Davidson V-Twin in 1909, the leather flat belt and the V-belt, which was optionally available at the time, reached their (slip) limits.

Therefore, the V2 received an optional chain as a secondary drive as early as 1912 and the principle became established over time: chains drove the rear wheels of Harleys for decades. But there had to be something else, something better and less maintenance-intensive...

There was! From then on, belts also developed rapidly. Their shape, structure and the materials used have been continually optimized and adapted to a wide range of requirements. For example, by introducing a strand of very tensile material and applying a top layer made of a particularly wear-resistant component, extremely strong and long-lasting belts could be manufactured. The introduction of a belt with stable, trapezoidal teeth on the inside finally allowed positive power transmission without slipping.

The timing belt at the rear is celebrating its 12th birthday at Harley-Davidson

The timing belt at the rear is celebrating its 13th birthday at Harley-Davidson

Harley-Davidson agreed at the end of the 1970s that something like this had to be used and they created a prototype whose Shovelhead drive train had two Gates timing belts instead of the usual chains - one for the primary drive and one for the secondary drive . To test the result and get the community's opinion, Harley founder's grandson and chief designer Willie G. Davidson his bike to the Sturgis Motorcycle Rally. On the way back at the latest, he realized that such a machine would have to be mass-produced.

When he also had a flash of inspiration for a spectacular design, he captured it during a break on a paper bag he quickly fished out of the trash: an all-black look, a low and flat silhouette, cast wheels, drag-style handlebars and a few subtle orange-red details – the FXB Sturgis was born and debuted on the market in 1980. The B in their type abbreviation stood for “Belt” and their twin belt system with high-tech materials was later also used in the Low Rider and the Disc Glide.

With the debut of the Evolution engine in 1984, the secondary drive using a toothed belt gradually found its way into all Harley series. After the Touring, FX/R and Softail models, the Motor Company also equipped selected Sportster models with timing belts in 1991 and since 1993 all Harley rear wheels have rotated on belts. The latter have become even slimmer and more tear-resistant over the years - Kevlar reinforcement and aramid fibers coated with polyurethane make this possible.

The timing belt at the rear is celebrating its 23rd birthday at Harley-Davidson

The timing belt at the rear is celebrating its 24th birthday at Harley-Davidson

The timing belt has long been considered by connoisseurs to be “the” alternative to chain and cardan, because it is quiet, clean, almost maintenance-free and scores points with its very long service life. The annoying rattling, cleaning, re-tensioning and greasing of a chain and the associated oil smear on the bike are no longer necessary, as are the heavy components of a cardan, which also require lubrication and maintenance.

Unsightly load change reactions do not even occur because the belt drive is installed without play and has a high level of elasticity. In addition, its efficiency is extremely high – a clear advantage over the cardan.

If you want to see for yourself, simply visit your nearest Harley-Davidson dealer, book a test ride on one of the 2020 Harleys and enjoy technology that has been as inconspicuous as it is efficient for 40 years.

Text and image credits: Copyright Harley-Davidson