Roller Clutch Blues

"Dear Ralph" December 27, 1996 0
Dear Ralph: I bought a roller secondary clutch kit last year based on all the good things I’ve been hearing, but I was not...

Dear Ralph:

I bought a roller secondary clutch kit last year based on all the good things I’ve been hearing, but I was not happy with the performance when I installed it. It just doesn’t run right, especially at low end. I know I haven’t got the calibration down yet, and I am starting to feel like I got hosed. My concerns are not being addressed by anyone, do you have any advice?

Michael Albrecht
Fargo, ND

Michael:
We have been using roller secondaries for three years now, and will admit that there is a steep learning curve when it comes to getting the calibration of the entire clutch system dialed in. It is all a matter of matching the shift curve of your clutches to the powerband of your engine. Easier said than done, but once you get it dialed in you will be happy.

You have to change your thinking when installing a roller secondary. Our experience has been that the roller unit upshifts so quickly that if you make no other changes the engine will be loaded too hard too fast, similar to installing too steep of a helix or having primary weights that are too heavy. If you bought the kit and were told that it would work with no other changes, then you’ve been had. By virtue of what the roller does (reduce the friction) you must make changes to the helix angle and spring rate to compensate for the change to the shift rate. The typical recommendation is to install a helix with a more gradual angle to slow the upshift (typically 5 to 7 degrees), and even after that you’ll likely have to increase the spring tension. On the smaller sleds (under 800 cc in this case) increasing the spring tension two or three holes will do the trick, or install a higher rate spring or even one that is longer for more side pressure.

The most common mistake is that after installing the roller kit the tuner is not willing to go tight enough on the secondary spring, as this goes against everything they’ve ever been taught. And how many tuners have a bunch of helixes that are shallower than what comes stock ? Most of them have steeper, more aggressive helixes which are the exact opposite of what they need. For example, if the sled comes with a stock 36 degree helix, installing the roller makes it shift as if there was a far steeper (like a 50 degree) helix in there. If the engine doesn’t have enough torque to pull this load, it will bog. Going to a shallower angle slows the upshift, allowing the engine rpms to build before the load is applied.

If you can not compensate enough by changing the helix angle and spring tension you could use the flyweights in the primary to get the calibration right. Lighter flyweights will not load the engine as hard, but will also raise the operating rpm. What you need is less weight on the initial shift area on the flyweight (up by the pivot hole) as the shift occurs (allowing the power to build), then throw more weight at the engine (more weight in the middle of the flyweight) as the power and load increases, and have enough weight at the tip of the flyweight to keep the fully shifted rpm where you want it. What you need, in comparison to a normal flyweight, is one with less mass at the pivot area, more mass through the middle, and the tip mass will depend on the engine.

If where you purchased the roller kit from does not have specific set up calibration parts or specs for your sled, you either need to have a box of helixes to play with (at varying shallower angles), have some higher rate springs to work with, be able to grind some weights, or be willing to experiment with some of the “adjustable weights” now on the market. Adjustable weights are available from Thunder Products, Hooper Racing, and Tri-City Polaris. They all use a different method of adjusting the weight, but they all allow you to vary the placement of weight along the arm (in varying degrees). Remember, it is a matter of matching your shift curve to the powerband of your engine. The roller secondary accelerates the initial portion of the shift pattern. A shallower helix slows it down, as does a lighter flyweight. Having less weight at the pivot area allows you to let the engine power build as the roller secondary quickly shifts. Finding the right combination throughout the entire powerband is the trick.

On our Arctic Cats we’ve been able to just go to a shallower helix angle (48 degrees) and increase the spring tension to take care of most of the bogging. On the Yamahas we also used a 48 degree helix but had to install a stiffer spring. With our Polaris engines, the low end torque was not great enough to pull the load, so a “reverse angle helix” like a 34-36 can be used with a blue Polaris spring. We also increased the engagement rpm to have more power available and used a set of adjustable flyweights to get an Ultra to work. Engines with lots of low end torque seem to respond far better to the rollers than do engines weak on the bottom.

Once you get the shift pattern matched to your engine (which is what the factory tried so hard to accomplish) you will be happy with your roller unit. Until then, you will be fighting bogging and over revving conditions, and I can understand your dissapointment.

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