The new harder-compound drive belts found on most of the new high performance models provide extreme durability and last extremely well.

The new harder-compound drive belts found on most of the new high performance models provide extreme durability and last extremely well. In fact, they will typically wear out prior to losing cogs or blowing. That is good for most of us, but we have seen this kind of extended durability lead to tuning issues because of the belt wearing instead of blowing. This drive belt will wear narrower and narrower, and as it does, performance will be lost a little at a time.

It will reach a point where the operating RPM will start falling off on long pulls, and tuners will check almost everything else but the drive belt itself. The drive belt should always be one of the first things you check when troubleshooting performance and operating RPM issues. The first question for those asking about consistency problems is, “How many miles does your belt have on it?” Usually, these riders have not changed their drive belt recently. They think the problem must be something else because the belt is still in one piece and visually looks okay. Just because it is in one piece with all of the cogs still there, it doesn’t mean it is still good from a performance standpoint.

Which means we should be more aware of the width of a brand new belt for your sled, so then as the belt ages and wears you can again check its width to see how much narrowing has occurred. It’s not going to take a whole bunch of wear to start to affect the point of engagement, as the clutch sheaves have to travel further (higher gear) to grab and engage the narrower belt.

With this in mind, once we start to see the width change by 1/16 of an inch (about sixty-two thousandths) we are going to start to really notice changes in performance. Many riders will be swapping out their drive belt before this time, but we had to give you an idea of what to be looking for. Remember, the side clearance between the drive belt and the primary sheave should be only 10-15 thousandths, so if the belt has worn by a full 1/16th of an inch we have really opened up the side clearance to the point the clutch is traveling a long ways to grab the belt!

Clean clutches and a good drive belt should always be one of the first things to be checked before going after more obscure and less likely causes of performance issues. Unlike a chain-drive machine, the belt drive CVT clutch system needs to be working properly for the engine to operate at the proper RPM level and for the shifting to occur properly. If the load to the engine exceeds its power capability, the engine will lose RPM and the sled will not perform properly. And when the drive belt narrows from wear, it is like screwing with the gear ratio. Instead of starting out in low gear, the sled will act like it is starting out in second gear, sluggish and slow to accelerate off the line.

Remember that brand new drive belts do have variances in their length and width, and there might need to be slight adjustments to the belt deflection and ride height to get it to fit properly (in comparison to the old narrow belt you just removed). Also remember that each new drive belt should be “broken-in” by taking it easy for like 30 miles to get it loosen up before giving it hell.

  • Norman Campbell

    December 21, 2016 #1 Author

    If the secondary is adjusted to close further (belt all the way to the top), it does not effect the starting ratio. Yes the primary gets a run at it, but if the belt is tension adjusted, the starting ratio will still be the same. It will not climb the primary all the way to the top anymore so the top end is lost. I don’t believe that the top is often achieved anyway. It is great fun to truly understand these clutches. They are far more complicated than we realize. Magic!

    Norm

  • Brian

    January 18, 2017 #2 Author

    I disagree with Norm. Unless you shim the primary as the belt wears, the starting ratio is affected by the narrow belt. The pick up diameter of the primary in creases as the belt narrows and the starting diameter of the secondary is only maintained by “closing” it further. Therefore the ratio is incapable of returning to wide belt ratios without shining the primary spider. JMO

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