High Performance Tuning Tips for your CVT Clutch
We love our continuously variable transmissions. Mr. CVT, if that was his name, invented a marvelously simple and effective way of transmitting power to the ground without the need for manual shifting, manual clutches or wildly complex hydraulics. This mechanism works on a very sound mechanical principal: magic. At least, that’s the way most ATV and side-byside owners think of the CVT, if they think of it at all. That lack of understanding has consequences. The CVT isn’t particularly high-level magic; it has to operate within the parameters of physical science. Centrifugal force, gear ratios, mass and leverage all come into play, and if we don’t understand that, the magic stops working.
A good example of all this can be found in our favorite RZR modifications and upgrades. Number one on the list of aftermarket mods is bigger wheels and tires. That’s great; they can make your machine look better and provide better traction. But larger wheels have the side effect of increasing the final drive ratio. It’s a little like putting your car’s manual transmission in top gear and trying to do a burnout. The result can be a loss of acceleration and short belt lifespan. The solution is to upgrade your clutch. Most people must not realize this, because clutch modifications are far, far lower on the list of aftermarket modifications.
Here’s the real irony: clutch mods are inexpensive and easy to perform. We recently installed an EPI clutch upgrade on a RZR 900. You’ll need a few specialized tools, as well as a good set of snap-ring pliers and an impact wrench.
Here are the parts we got from EPI. The Sport Utility kit for oversize tires includes new springs for both clutches, weights for the primary clutch and a new helix for the secondary. We also got a new Severe Duty belt, a puller and a spring compressor. EPI Performance.com can direct you to which kit you need, and most retail for around $329.95.
Davin Gothard of DG Offroad Center helped us install a clutch on our test RZR 900. Davin builds and installs excellent roll cages, but was happy to venture outside his comfort zone for our project. Check out www.dgrhinos.com to see his work.
The first step is to remove the CV cover. On the RZR 900, it’s on the left. You’ll find it easier if you remove the wheel and the bottom or top shock mount.
The primary clutch is the one in front on the motor. It engages when the motor rises above idle, and is controlled by three weights and a spring. The secondary clutch in the back changes the final drive ratio as wheel speed increases. With our 30-inch tires, 27 inches is stock, our RZR would be overgeared if left alone. The EPI kit corrects this.
Polaris provides a tool that lets you relieve belt tension so it can be removed. The primary clutch itself is easy to remove with a puller. The EPI part number is PCP8, and it sells for $59.95. Install the puller in the center and use an impact wrench to tighten it.
The primary, or drive, clutch is under spring tension, but can be disassembled without special tools if you are careful. In this case, we used the EPI clutch-spring compressor to relieve the pressure while we removed the six bolts. This tool is much more essential for the secondary clutch, but it worked well here too. Before disassembly, mark the clutch, the spider and the pressure plate so they can be assembled in the same orientation.
Once you have the clutch apart, you’ll see this spring. It has a replacement in the EPI kit.
There are three weights within the primary clutch that need to be replaced. Simply remove the pivot bolt on each and reassemble with the new EPI weights. Reassemble the primary clutch and move on to the secondary.
Taking the secondary clutch off doesn’t require a puller, but an impact wrench will be handy. There will be shims behind the clutch, so be careful not to lose them.
Flip the clutch over and you’ll see the helix. This has to be removed first, but the four Torx screws will be stubborn. We suggest having replacements handy, because you’ll probably mess the original ones up slightly.
With the helix removed, you’ll see a snap ring. This is under pressure, so you’ll have to use that spring compressor. The EPI part number is CCT510, and it sells for $89.95. It takes a really good set of snap-ring pliers to handle this particular snap ring—it’s burly!
Remove the shaft, and now you’ll see the secondary clutch spring. It gets replaced. When you reassemble the center shaft, the splines have to be aligned properly. You’ll put the new EPI helix in when it goes together. This changes the backshifting and engine-braking characteristics. Use blue Loctite on the helix screws.
Reinstall the two clutches and tighten by hand. About 50 pound-feet is usually good, but it varies by model. When you install the belt, make sure the lettering reads from left to right and isn’t upside down.
Reinstall the cover, the shock and the wheel, and go have fun!