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Customers with 1200 triples had already started to experiment with aftermarket clutches to solve the problem though, and many chose older style power block clutches. These did not have the calibration ability of flyweight and roller clutches, but the simpler blocks and lower inertia seemed to have a longer wear-life. The broader power band of the 1200 4-stroke engines made them work acceptably on this application and made them a popular stopgap while Ski-Doo beefed up its eDrive clutch.
The new eDrive 2 clutch is the result of an intense effort to produce a clutch that can handle the 4-stroke load requirement. With six flyweights and 12 torque transfer buttons the loads are now cut in half for each component and the wear surfaces are doubled.
Roller arm shaking was a problem with the TRA clutch, especially since the roller assembly had to be heavy to handle the higher torque load of the 4-stroke power. This load is now divided between six much lighter weights, which are better matched to the torsional signals from the crank and do not pick up these vibrations as readily as the heavy TRA roller arms. The flyweights also are guided by vesper washers on each side. The mounting slot is machined to control the washer and flyweight side play tolerances for much improved durability. The flyweight and roller relationship is much different than conventional snowmobile clutches.
While Polaris moved the spider out to give the flyweight a more aggressive angle at lower shift ratios, Ski-Doo has moved the roller up to let the flyweight pivot out more. As a result, the flyweight profile is quite different than what we are used to seeing. The curvature is almost straight and the flyweight has a thinner body and heavier tail. This matches the strong torque requirement of the 4-stroke engine in the low- and mid-rpm ranges.
On the eDrive 2, the moveable sheave is beefed up to match the 1200 4-TEC power and the sheaves also are larger in diameter than those on the ATVs, for more ratio. The shafts also are stiffer and have larger sliding bushings.
A new feature is a steel insert on the sheaves in the lower ratio, which reduces wear and improves friction, gripping the belt better in the high torque, low ratio and engagement speed range. This becomes a large problem with aluminum sheaves as they usually wear a groove quickly on the bottom, which can require buying a completely new clutch. This steel insert is replaceable and inexpensive and should solve a major wear issue.
As the 4-stroke applications evolve in our industry, expect to see many more developments on the clutch side of the powertrain. There are as many different approaches to this problem as there are manufacturers, and we can expect to see an interesting variety of solutions in the future as 4-stroke powered snowmobiles evolve.