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FIX IT: CVT belt tips and what breaks them

When you are breaking in a belt, you want to avoid hard throttle applications and full-load situations like this.
November 18, 2016
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Dirt Wheels spends a lot of hours and miles in CVT (continuously variable transmission)-powered vehicles every year. As CVT-powered ATVs and UTVs have proliferated, knowledge of the system has grown exponentially as well. Dirt Wheels actually had a CVT belt guide before the Polaris RZR XP 1000 came out, and at that time belt life was just becoming an issue we heard a lot about.

The belt world changed when Polaris introduced the RZR XP 1000 and hit DEFCON 1 with the RZR XP 4 1000. Since then we have seen the turbo models from Can-Am and Polaris with as much as 140 horsepower hooked to the wheels with a belt. A serious and well-engineered belt, but still a rubber and cord belt. As the power has gone up, so has the weight of the machines, and the combination has resulted in belt issues becoming more common. CVTs are still a great and simple answer for power transmission, so we wanted to share some of the excellent CVT belt knowledge that is out there.

When you are breaking in a belt, you want to avoid hard throttle applications and full-load situations like this.
When you are breaking in a belt, you want to avoid hard throttle applications and full-load situations like this.

GETTING STARTED
All-new machines are supposed to get a break-in period. Polaris says to run new UTVs easily for the first two complete tanks of fuel. During that time be smooth on the throttle, don’t lunge at low speeds and don’t run at sustained steady throttle settings. Stop often and let the engine cool off (heat cycle). A good break-in is great for the life of the car, and it helps belt life as well. The belt likes a similar break-in. If the belt is broken in properly, it should last a long time.

Most modern CVT cases have inlet and outlet vents and often filters on the inlet vents that are necessary for good belt life. Running with the vents blocked or restricted will make the belt run hotter—and heat is a belt killer. Polaris changed the belt case and venting on the 2015 and 2016 RZR XP 1000 models to aid belt cooling. You can upgrade 2014 models with the Polaris high-flow clutch intake system. The kit converts the 2014 Polaris XP 1000 and XP 4 1000 models to the 2015 clutch-intake setup. The kit is available from dealers, but we saw it on the Rocky Mountain ATV/ MC website as well. The kit includes everything needed to install it. With redirected and improved airflow, belt life is substantially longer. The kits include a factory drive belt (Polaris part #3211180), a clutch cover, Frog Skin in-take covers, intake tubes, mounting hardware and instructions. With the kit installed, you need to stick with the #3211180 belt specified for the later-model RZR 1000s. Some brands of UTVs actually have air pumped into the CVT case, and some racers are fan-forcing air into the CVT case to keep belt temps down.

You don’t have to be going fast to abuse a CVT belt. Climbing under a load in high range is very tough on the belt.
You don’t have to be going fast to abuse a CVT belt. Climbing under a load in high range is very tough on the belt.

NOT JUST SPEED
Driving slowly with a high load and the transmission in high range will toast the belt, and so can riding or driving with the brake on. You have a different problem with a similar result if the wheels are stuck. When you hit the throttle, the drive clutch spins but the belt doesn’t. That burns the belt in one spot. It may not fail right then, but belt life is shortened. Water, mud or dirt in the CVT case, and especially on the sheaves (the drive faces of the clutches), all hurt belt performance and shorten the life of the belt. Having the belt too tight or loose will affect performance and belt life as well.

CVT belt manufacturer Dayco suggests, “Keeping your clutches clean will help improve performance and avoid clutch and belt wear. Lightly sand your clutch sheaves [faces] with fine sandpaper or emery cloth. You must sand from the center out to the edge. Work your way around both sheaves. Do not sand any grooves into the clutch sheaves.

“Sanding the sheaves will remove belt residue and give the belt a better surface to grip. Once you are done sanding, blow off any sanding dust from both clutches. Take contact or brake cleaner and clean the entire clutch, except for the bushings. Do not use contact cleaner on any of the clutch bushings. Choose a contact cleaner that does not leave an oily film when it dries.

“Wipe the bushings off with a clean, dry cloth. The inside hub of the helix is the only area where a small amount of grease may be applied. Clean your clutches every time you have them apart and/or several times a season.”

WHAT IT IS
A CVT belt is a type of V-belt. As such, it is the side of the belt that is doing the work much the same way the tread on a tire does. The sides of the CVT belt use the faces of the sheaves for traction. For that reason, the angle of the side of the belt must be perfectly compatible with the faces of the CVT. The width of the belt must be precise as well.

The belt’s cord is in between the bottom cog and the top cog. The bottom cog is faced with material.
The belt’s cord is in between the bottom cog and the top cog. The bottom cog is faced with material.

WHY AND HOW
Carlisle engineer Eric Murray elaborated on the task facing a CVT belt: “The clutch/belt system has to do a few things simultaneously. First, it has to transmit all the power the engine can put out. If you have a big side-by-side that’s putting out up to 140-plus horsepower, all that power goes through the belt. The clutch squeezes the sides of the belt hard enough to accelerate the machine and whatever it’s loaded with. This means there can be over 1000 pounds of squeeze force trying to crush the belt from the sidewalls. At the same time, it’s rotating fast enough to spin the secondary clutch, in some cases, over 9000 rpm. Simultaneously, it’s shifting up and down in both clutches to deal with changing loads, both from the engine and back through the drivetrain from the wheels. It does all this while running at temperatures ranging from minus 30 to over 200 degrees. It’s a hard life.”

CVT belts need to be heavy duty but also precision-made. The side angle of the belt must match the CVT sheaves.
CVT belts need to be heavy duty but also precision-made. The side angle of the belt must match the CVT sheaves.

WHAT TO DO
At some point you will probably need to change a belt, and that time may arrive on the trail. Make sure you have a spare belt along, as well as the tools to change it. We’ve all seen a spare belt zip-tied snugly to the roll cage, but belt companies claim that forcing the belt that tight is not good for it.

If you are starting with a new belt (at home), it is beneficial to wash new belts in dish soap and water before installation. Washing gets rid of some of the loose rubber and mold release that may be on the belt from manufacturing. Let the belt dry before using it or storing it. If the belt you are prepping is going to be carried as a spare, put it in a 2-gallon sealable plastic storage bag or some type of clean container. We like the DragonFire Racing belt bag.

Try to log 30 to 40 easy miles to break in the belt. Downshift to low range to reduce belt load if you are climbing. You don’t want the belt to sit in one place on the clutch sheave surface for an extended period. Stop and let it cool about every 15 minutes. Be smooth on the throttle through break-in, and don’t run a heavy load (eject a couple of passengers if you’re driving a four-seater).

Large tires, heavy tires and wheels, and engine modifications often require clutch modifications.
Large tires, heavy tires and wheels, and engine modifications often require clutch modifications.

BEYOND BREAK-IN
If you have a unit that has a history of breaking belts, you may want to have the shaft alignment checked. If the shafts are out of alignment, you will suffer premature belt failure. We will be testing a SDI belt alignment tool for the Polaris XP 1000 soon. Inspect the belt prior to failure. You may see wear on one side wearing to the cords and not the other side. If you see lopsided wear like that, you may have alignment issues.

If you shred a belt, it is vital to clean out all of the remnants. Long needle-nose pliers are great for this chore. Make sure you remove the exit vent hose, because most times you’ll find debris trapped in there. If you don’t clear it, it will work its way back into the CVT area and raise havoc.

Some experts claim that belts are directional. Always install the belt so that the writing on the belt is facing you. That way, if you end up using a used belt for a spare, you will install it in the same direction it was run before. If you find a belt that has been installed “backwards,” don’t rotate it; leave it running the same direction. Never power-brake a CVT vehicle. Even at the start of the race, when you do that, the rpm is up but the belt is not spinning, and it puts flat spots in the belt.

Check your machine’s sheaves. If they have wear or grooves, you won’t get optimum performance, and you’ll prematurely wear the belt.

This lower-powered machine doesn’t require a heavy-duty belt like a powerful UTV does.
This lower-powered machine doesn’t require a heavy-duty belt like a powerful UTV does.

CHOOSING A BELT
Most stock CVT belts are of very high quality. Often they are expensive compared to aftermarket belts. Many customers choose to stick with the stock belts, but others swear by aftermarket brands. Some performance companies have their own belts (usually private-labeled from a belt manufacturer), or they recommend a specific belt. Belt technology has had to accelerate as the power output of CVT-equipped machines rises. Did you notice that extreme-duty belts appeared shortly after high-horsepower UTVs did? ATVs do need replacement belts, but not at the rate that UTVs do.

The belt is made from rubber (usually fiber-reinforced) that is rigid across but flexible along the length. The “cog” or toothed look on the inside helps the belt resist the extreme compression and allows a greater traction surface yet still bend easily. The cog on top aids bending around the pulleys, adds side traction, makes the cross section strong and generates cool air in the CVT case. Between the top cog and the inner cog is the cord. The cord gives the belt the strength lengthwise. The cords are bound into the fiber-reinforced rubber of the cogs with adhesive. The face of the cogs has a fabric cover.

Sand, a heavy and powerful machine, and a hill to climb— all together they make a CVT belt cry for mercy. Breaking in the belt properly, keeping belt temp in mind and driving smart will help the belt live.
Sand, a heavy and powerful machine, and a hill to climb— all together they make a CVT belt cry for mercy. Breaking in the belt properly, keeping belt temp in mind and driving smart will help the belt live.

HEAT IS THE ENEMY
The consensus in the industry is that belt temperatures over 200 degrees are bad and 400 degrees is critical. Some racers use a belt-temp gauge, and they drive the race car while watching the belt. If temps rise, they back off to allow the belt to cool. High-end SxS racing, high-horsepower machines with paddle tires and mud boggers with tall, aggressive tires are the hardest machines on CVT belts.

Engine mods, big tires and a heavier machine all add to the heat that the belt must endure. If you start to make changes like these, then you need to make changes to the clutching to keep the heat down. You want to avoid extended running at one throttle position. If you’re rolling down a graded road for miles, you want to cycle the belt up and down the sheaves a bit. Basically, throttle up and down as you are rolling along. Extended wide open is even worse. When the clutch finally shifts all the way out, it loses pressure on the belt, and that can lead to slipping.

Large-diameter tires put more load on the belt and CVT. Modern CVT covers are vented like this one is.
Large-diameter tires put more load on the belt and CVT. Modern CVT covers are vented like this one is.

CONCLUSIONS
Changes in the most modern machines, more available knowledge about belt issues and more educated drivers are all helping belt life. Follow the advice from the experts on how to avoid belt issues. Most of the problems noted occur frequently only in extreme use or, as in the case with riding too slow in high range, from improper riding technique. There is a reason that the CVT is so common: it works. If you are having serious and frequent belt problems, check that the clutches are working as they should mechanically. Consider an extreme-duty belt, and check into having the clutches fine-tuned for your riding conditions. Make sure that the belt deflection is inside the manufacturer’s specifications. Keep belt cooling in mind, and make sure that the factory vents are not hampered in any way. Then, have fun!

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