the good and the bad of modern secondary clutching

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Best of both worlds
Polaris considered this possibility when they developed the new P2 secondary. Polaris offers the new P2 clutch with provision to use both straight pressure springs and “tabbed” torsion springs. Both the helixes and movable sheaves have holes for mounting torsion springs, and Polaris offers both 7 straight pressure springs and 4 tabbed torsional springs. The tabbed torsional springs will not have quite as much side force preload, but the reverse notch on the helix is angled to provide pressure during reverse rotation. I have not heard of any problems with reversing a P2 with a tabbed torsion spring installed. On the other hand, those of our customers that converted P2’s from pressure springs to tabbed torsional springs all reported better acceleration, higher top speed and quicker back shifts on par with the Arctic Short Tower roller units. The P2 unit is also well designed with active air flow through the unit to cool down the parts and a nice spread between the sliding bushings on the movable sheave.

The Ski-Doo XP QRS secondary is also a well designed roller clutch with encapsulated helix that offers an electronic reverse action notch. This unit does come with a tabbed torsion spring and as a result combines quick backshift and hard acceleration with good top-end speed. Unfortunately, in the quest for weight reduction, the fixed sheave is part of the secondary shaft. In order to take the clutch out you must remove the whole secondary shaft with it. Changing the helix and spring can be done with the unit in the sled. It’s just a little harder to get to the parts than if the unit could be removed and worked on in a fixture.
For racers, Ski-Doo offers a standard secondary shaft where a TEAM clutch can be mounted in the conventional way. Several aftermarket companies offer Ski-Doo secondary shafts that will accomodate a number of different clutches. This is for those people that have a favored setup which they perfected over the years.

It is somewhat concerning to me to see what amounts to a “backward” development from what was considered essential for good efficiency over the last 40 years. This is basically due to the great improvement in belt designs the last 25 years. In the ’80s you would only be able to transmit up to 120 HP before the belt problems occurred. With the new wider top-cog belts and the new stronger cords you can now transmit twice that power without a problem. This has resulted in a change in design philosophy. While before designers would not even consider using straight pressure springs for concern of over loading the belts at full shift outs on the top end, the belts are now so strong that this is less of a problem. As a result, a new generation of clutch designers feels some efficiency and performance can be sacrificed for easier assembly of the unit. We’re sure there are a few weekend riders who feel the same way.

Those that want the ultimate performance on the trail and at the race tracks can still go back to the more efficient torsional spring designs. If you have belt problems with a high-horsepower turbo charged machine, you might take a good look at what’s inside the secondary, and possibly consider converting back to earlier and more efficient torsion springs units.
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