SOME THOUGHTS ON QuickDrive® BELT ISSUES

mountainhorse · Nov 13, 2012

SOME THOUGHTS ON QuickDrive® BELT ISSUES

Here is my take on SOME of the belt quandry out there... This may be more than you care to read.

There have been a few photos posted of sheared final-drive belt teeth on some Polaris QuickDrive equipped 2013 PRO RMK's.

So that we are clear... There are only a FEW documented issues of stripped belt teeth at this point in time. This is not a widespread observation .. but certainly one that is much discussed lately.

There are plenty of riders out there on their 2013 PRO RMK's that have not had any issues with their QuickDrive belts... including some turbo riders like Matt Entz and Erik Woog.

Also, I hope that the P.I. engineers that may read this do not take this in any kind of an offensive way.. and If the assumptions I make here are off-base...please contact me by email or PM and I will make the necessary corrections.

I have also heard that Chris Burandt and Polaris RMK engineers that there had been some sheared tooth belt failures during development, and that this was worked out on production sleds for the 2013 MY.

The engineers said that the only "failure mode" that they saw with the QuickDrive belts was with seared teeth while under abnormally high shock loads well beyond the normal operation of sleds by consumers.

I believe these QuickDrive belt failures only represent a small portion of the units out there and for the most part, the QuickDrive will be trouble free....AND in the end.. only time will tell and we should have an accurate picture of system durability.

I have some, limited, design experience with Gates Poly Chain GT drive systems, outside of the snowmobile world.

The most recent drive CMX drives using the Gates Poly Chain drive have not experienced sheared toot failres that I have heard of... But the CMX system is a very different design than that of the QuickDrive. The C3 drive also differs in that it has a tensioner.

The tensioner as equipped on CMX and C3 drives, IMO, does NOT have as its primary function to adjust for a stretched belt.

Except for a minute initial & Permanent stretch... The Gates Carbon Poly Chain belts do not stretch for all intents and purposes... they will break before they stretch to any significant degree.

The primary advantage of a tensioner is to accommodate mfg. tolerances and tolerance-stacking inherent in a fixed Center Design and to accomodate different drive ratios.

Accurate tensioning methods will be crucial to getting proper performance from aftermarket drives... And is one of the reasons that some of the belts on older CMX drives were breaking...installer error in proper tension.

I also like the use of an inside idler/tensioner of the CMX drive compared to the backside tensioner of the C3 drive in terms of reliability.

Note: A tensioner can help to adjust for tension issues in a "fixed center" design and provide more optimal tooth engagement in cases where tolerance stacking, variations in manufactured measurements are present.

In effect, this changes the design to a hybrid-non-fixeddesign that can be adjusted to accommodate these variances.

Here are some of my theory's for these few belt failures that have appeared in consumers sleds.

1) The demo and Press units that were used last season were hand built units. Yes, they were made on the production line according to Polaris and I trust this info. But they would receive extra care and the original parts are most likely individually checked for tolerance in mfg. Which leads to...

2) Tolerance built into drive to accommodate fixed center. As you will read below.. over tensioning of a belt is the worst case for these belts... but a loose belt can also overly self tension.

By design, and as indicated by the fact that you can slide (using the guide tools) a belt/sprocket onto the shafts when unloaded... the factory has built in a bit of looseness to the system to accommodate tolerance issues.
Some of the belts that are shearing teeth may be a victim of this or the minor off-spec situations that are inherent in ANY mfg process of mass produced vehicles.

We are talking about 0.002" - 0.003" here!

I believe that the urethane drive sprockets that have been successfully used in Harley Davidson drive sprockets could be very helpful in this situation... they have enough "give" to allow for these minor off-spec issues (C 2 C dimensional variation) and also absorb shock loads of sudden braking, reverse spikes, or instant track loading from jumping etc.

The sprockets that are offered by http://www.supermax.net/ are a good example of this type of sprocket.. and there is a great technical discussion here as well... check it out.

3) Operational-environment concerns... At high shaft and belt speeds debris or even water that could cause "hydroplaning" of the belt at high belt speeds causing over tension. This is not present in the final drives of belt-driven road bikes because of the relatively lower belt speeds of a large diameter tire/wheel.

This is where I believe that the use of vented or ported sprockets would be helpful. Unvented sprockets, may not allow for the exit of water/ice quickly enough to prevent hydraulic lifting of the belt around the contact-arc of the belt on the pulley... which could result in a destructive over-tensioning situation simultaneously occurring with less belt to sprocket engagement.

4) Drive shaft wobble or bent drive shaft.
If the QuickDrive end of the driveshaft is not true and has some wobble to it... the belt will cycle through over and under tensioned issues. A new driveshaft that has suffered impact damage will run "out of round" at the sprocket... A simple dial indicator can verify how true the shaft is running.

Even a hit that only temporarily deflected the shaft can cause an over-tension situation to occur and could cause a situational failure of the belt or bearings.

Impact damage is more likely in a drop/roll situation where the drivers/shaft are more exposed to impacts than a stock installation. In this case... a D&R mfg may want to consider a bash plate/wedge in front of the driveshaft to minimize the possiblilty of impact damage/bending.

In the end, I still believe that most will have trouble free operation of their sleds this year...This is a discussion for those people that have posted sheared belt issues. I'm also confident that P.I. will cover most these low mileage belt faliures under warranty on a case-by-case basis.

mountainhorse · Nov 13, 2012

From Gates PC_Carbon_Manual 17595 2011

11. Fixed (Nonadjustable) Center Distance
Designers sometimes attempt to design synchronous belt drive systems
without any means of belt adjustment or take up. This type of system is
called a Fixed Center Drive.

While this approach is often viewed as being economical, and is simple for assemblers, it often results in troublesome reliability and performance problems in the long run.

The primary pitfall in a fixed center design approach is failure to consider the affects of system tolerance accumulation. Belts and sprockets are manufactured with industry accepted production tolerances. There are limits to the accuracy that the center distance can be maintained on a production basis as well. The potential effects of this tolerance accumulation is as follows:

Low Tension:
Long Belt with Small Sprockets on a Short Center Distance

High Tension:
Short Belt with Large Sprockets on a Long Center Distance

Belt tension in these two cases can vary by a factor of 3 or more with a
standard fiberglass tensile cord, and even more with an aramid tensile cord.
This potential variation is great enough to overload bearings and shafting, as well as the belts themselves. The probability of these extremes occurring is a matter of statistics, but however remote the chances seem, they will occur in a production setting.

In power transmission drives, the appearance of either extreme is very likely to impact drive system performance in a negative manner

The most detrimental aspect of fixed center drives is generally the potentially high tension condition.

This condition can be avoided by adjusting the design center distance.

A common approach in these designs is to reduce the center distance from the exact calculated value by some small fraction.

This results in a drive system that is inherently loose, but one that has much less probability of yielding excessively high shaft loads. NOTE: This approach should not be used for power transmission drives since the potentially loose operating conditions could result in accelerated wear and belt ratcheting, even under nominal loading.

There are times when fixed center drive designs can’t be avoided. In these
cases, the following recommendations will maximize the probability of success.

1. Do not use a fixed center design for power transmission drives.
Consider using a fixed center design only for lightly loaded or motion
transfer applications.

2. Do not use a fixed center design for drives requiring high motion
quality or registration precision.

3. When considering a fixed center design, the center distance must be
held as accurately as possible, typically within 0.002”— 0.003”
(0.05mm — 0.08mm). This accuracy often requires the use of stamped
steel framework.

4. Sprockets for fixed center systems should be produced with a machining process for accuracy. Molding and sintering processes are generally
not capable of holding the finished O.D. sufficiently accurate for these
systems.

...

12.
Use of Idlers

Use of idlers should be restricted to those cases in which they are functionally necessary. Idlers are often used as a means of applying tension when the center distance is not adjustable.

Idlers should be located on the slack side span of the belt drive. General size recommendations are listed for inside grooved, inside flat, and backside idlers. In some cases, such as high capacity drives utilizing large
sprockets, idlers as large as the smallest loaded sprocket in the system may be more appropriate.

...

mountainhorse · Nov 13, 2012

Gates PolyChain GT2 Design Manual, Page 110:

"All synchronous belt drives exhibit a self-tightening property when transmitting a load. Lab testing has shown this property is similar for all tooth profiles. The designer should be aware that self-tensioning can result in increased bearing and shaft loads, as well as reduced belt life. These effects can be AVOIDED by following proper tensioning procedures."

"Belt overtensioning can impose unnecessarily high bearing and shaft loads. However, belt undertensioning results in self-tensioning. When a belt is too loose for the design load, the belt teeth try to climb the sides of the sprocket grooves, which dramatically increases the stresses on the belt, the belt teeth and the shafts and bearings, leading to rapid tooth wear and reduced component life."

From the Gates "Synchronous BeltFailure Analysis Guide"

Heat Degradation
When rubber belts operate at elevated temperatures (greater than
185°F) for prolonged periods of time, the rubber compound gradually
hardens resulting in back cracking due to bending. These cracks
typically remain parallel to the belt teeth and usually occur over land
areas (in between belt teeth).

High-temperature rubber belt constructions are available for belt drives
that must operate in high-temperature environments. These special
belt constructions help to improve belt service. To determine if a special
high-temperature belt construction will improve the belt performance in
specific applications, contact a Gates Representative.

Belts generally fail due to tooth shear , which can lead to tensile cord fracture.

The body material used in urethane belts such as Poly Chain® GT®
Carbon® belts is thermoplastic, meaning it has a melting point. When
subjected to environmental temperatures in excess of 185°F, the teeth
may begin to soften and deform. In addition, the tensile cord to urethane
adhesion loses its integrity. Figure 18 illustrates a Poly Chain® GT®2

...

It is possible that Polaris uses the higher temp belts pointed out above.. would like to see what one of these stock QuickDrive belts does when you put it in boiling water (212°F) and checked the tooth attachemet/softness.

mountainhorse · Nov 13, 2012

From EPI Inc.

Preload in a toothed-belt system is required in order to keep the teeth from attempting to climb up the sides of the grooves in the sprockets, and, in extreme cases, from jumping ("ratcheting") under the most severe loading conditions.

In a static (non-moving) toothed-belt drive, the tension force in each span of the belt is equal, and is determined by the required preload. The required preload is determined by four factors:

the number of teeth engaged on the driving sprocket,

the pitch diameter of the driving sprocket,

the maximum torque to be transmitted by the drive, and

the recommended tension ratio.

If the preload of a toothbelt is slightly less than required, the teeth will try to climb the sides of the grooves at high torque loadings, which leads to (a) rapid wear of the belt, and (b) very high shaft bending loads (higher than if the preload were correct).

Belt manufacturers recommend that the tension ratio for a system with more than a defined minimum number of teeth in contact on the smallest sprocket should be in the range of 8:1 to 10:1 (after the belt has run-in).

AgentRmk · Nov 13, 2012

Great Info!!

paulharris · Nov 13, 2012

mountainhorse said:
...

Great info, thanks!

paulharris · Nov 13, 2012

4. Sprockets for fixed center systems should be produced with a machining process for accuracy. Molding and sintering processes are generally not capable of holding the finished O.D. sufficiently accurate for these systems. said:
...

Interesting.....polaris uses cast sprockets. if there happens to be some "out of round" ones this could chew up belts

whoisthatguy · Nov 13, 2012

Motorcycle belt drives are never used for breaking. Polaris's belt drive does. It is conceivable that a greater shock load is applied to the belt teeth on the smaller top sprocket from braking, as could ever be applied from the rolling up of power from the engine through it's drive belt and clutches. During hard braking, the belt teeth would be called upon to stop the momentum of both the spinning track and the entire forward moving sled. Therefore, hard braking maybe the critical load case for the drive belt teeth, which never occurs with motorcycles that have belt drives. If the snowmobile brake was attached to the lower belt sprocket instead of the upper, then these braking shock loads would not be nearly as severe since the clutch belt stands between the engine and the top sprocket of the belt drive, to dampen the only remainly cause of shock loads to the belt drive.

Solution for sheared belt drive teeth. Never use the brake!

Going West · Nov 13, 2012

Thanks for posting, theres some real good info here. But when I read stuff like this it get me a little angry.

mountainhorse said:
There have been a few photos posted of sheared final-drive belt teeth on some Polaris QuickDrive equipped 2013 PRO RMK's.

I have also heard that Chris Burandt and Polaris RMK engineers that there had been some sheared tooth belt failures during development, and that this was worked out on production sleds for the 2013 MY.

The engineers said that the only "failure mode" that they saw with the QuickDrive belts was with seared teeth while under abnormally high shock loads well beyond the normal operation of sleds by consumers.

It basically means that there were failures during testing and instead of addressing the problem they just made excuses and assumed that the customers will never load the sled that hard.

Yes I agree that a rider like Burandt will be harder on his stuff then the average consumer, that's why they give him sleds to test, but when they do fail you cant just ignore the issue and say its just cause he rides harder then most. That is defeating the whole purpose.

mountainhorse · Nov 13, 2012

It will be interesting to see the performance history of the C3 drives, with the brake on the jackshaft, after some months of riding/abuse on converted sleds ... Say in March or April.

C3's "Syncro Drive" has a tensioner to allow for adjustment to compensate for the manufacturing tolerances mentioned above.

.

mountainhorse · Nov 13, 2012

Going West said:
It basically means that there were failures during testing and instead of addressing the problem they just made excuses and assumed that the customers will never load the sled that hard.

Yes I agree that a rider like Burandt will be harder on his stuff then the average consumer, that's why the give him sleds to test, but when they do fail you cant just ignore the issue and say its just cause he rides harder then most. That is defeating the whole purpose.

My point was that this was in the development stage and that they worked on the design so that it was not an issue... that is the accurate description of what I was told.

In the end... the design was well tested and adjusted to deal with any failure-mode issues.

"Well beyond" would hold true for people, like snowcrossers, that break chains or extreme mountain sledders that have done the same thing with chains.

I'm not privy to the development and evolution of this drive system in the past few years... BUT... I do want to have an ACCURATE discussion here.

Also, there are not enough documented cases of belt failure to make an evaluation of system integrity on consumers sleds, one way or the other, at this point.

Originally Posted by mountainhorse

There have been a few photos posted of sheared final-drive belt teeth on some Polaris QuickDrive equipped 2013 PRO RMK's.

I have also heard that Chris Burandt and Polaris RMK engineers that there had been some sheared tooth belt failures during development, and that this was worked out on production sleds for the 2013 MY.

The engineers said that the only "failure mode" that they saw with the QuickDrive belts was with seared teeth while under abnormally high shock loads well beyond the normal operation of sleds by consumers.

knifedge · Nov 13, 2012

mountainhorse said:
From Gates PC_Carbon_Manual 17595 2011

...

-- #1 (the very first) rule in post #2 above from the Gates Manual specifically states:

"Do not use a fixed center design for power transmission drives. Consider

using a fixed center design "ONLY" for lightly loaded or motion transfer

applications."

--Polaris broke the #1 (very first) rule of designing a belt drive and apparently assumes the average user will not load the belt drive beyond a lightly loaded and/or motion transfer application. Appreciate the research here, as it needs to be politely pointed out a design change is in order.

--To assume the average user will not load the belt drive like Chris Burandt or others is ridiculous, as these guys
actually make, promote, and sell videos on showing people how to do it, not to mention aftermarket parts available.

--If a Polaris engineer can strip a belt while riding, I would think an "average" consumer out West could do the same. Just saying.

--

--All this being said, it should be easy enough to redesign, the cost will come from updating existing sleds.

likkerpig · Nov 13, 2012

Burandt is a Polaris puppet, no offense but we all know he is compensated by Polaris to say what they want him to say. He is a marketing tool used to promote polaris' products. Understand that he is endorsing it but really any manufacturing issues are not his deal and he isn't liable if they don't hold up. That's the game- its all in how you say what you say.

Matte Murder · Nov 13, 2012

MH great info. But the failures that I read about appear to be from none of the causes listed. Guys out for a break in ride in moderate snow conditions. I wasn't even going to buy a spare belt "everyone is being Polarisnoid(did I just coin a new word?) about these belts". I know the internet magnifies problems like this but the negatives are stacking up. Engine, driveshaft and now belt. This could turn in to a total disaster for Polaris. They could very well snatch defeat from the jaws of victory.

Going West · Nov 13, 2012

mountainhorse said:
My point was that this was in the development stage and that they worked on the design so that it was not an issue... that is the accurate description of what I was told.

In the end... the design was well tested and adjusted to deal with any failure-mode issues.

"Well beyond" would hold true for people, like snowcrossers, that break chains or extreme mountain sledders that have done the same thing with chains.

I'm not privy to the development and evolution of this drive system in the past few years... BUT... I do want to have an ACCURATE discussion here.

Also, there are not enough documented cases of belt failure to make an evaluation of system integrity on consumers sleds, one way or the other, at this point.

I totally agree that this needs to be discussed in a rational matter without getting carried away with the internet hysteria. But it is clear that there has been some issues already experienced with this new drive system and to hear that they had the same issues during development is a little disheartening. The line that they have sorted it out for the production sleds does not make me feel any better when the same problems are surfacing very quickly on the production models.

Like you said it is a little too early to be calling this a major problem but it is just as silly to pretend that there isn't some sort of issue here.

Daltech · Nov 13, 2012

A friend of me have the C3 beltdrive in his 320hp Ski-doo 1200 turbo.
It holds up fine at that power level. So there's no reason Polaris should not get this to work, even if they have to copy c3 og cmx system to do it.
Now, I would whish cat atleast tried to make a sled that was innovate.

nuggetau · Nov 13, 2012

The part number on the QD belt is 3211146, which seems to be a drive belt used on one of the victory motorcycles (can anyone tell me which one?). Now Polaris has updated(superceded) the part number to 2204967. I am wondering if Polaris didn't have a large inventory of these old Victory belts that they chose to use up before delivering the new 2204967 belt? I have no proof that is what happened.

This is why I want to know what motorcycle this belt was used on, if it was a bike made several years ago, that would lend credence to the theory that these belts are very old stock? Maybe?

mountainhorse · Nov 13, 2012

Matte Murder said:
MH great info. But the failures that I read about appear to be from none of the causes listed. Guys out for a break in ride in moderate snow conditions.

I believe that those that were just breaking-in their sleds fit well into the description above, and would describe reasons why most are not having any problems with this belt.

.

Powerage · Nov 13, 2012

The belt on a victory bike is fairly long. The belt was designed and used only on the polaris snowmobile as far as i know. Nowhere on a motorcycle uses a belt that short.

mountainhorse · Nov 13, 2012

Nugateau...

I'm not well versed in the bikes by a longshot... but don't see any of the bikes with a divorced engine/trany that would be able to use such a short belt.. the ones from the drive to driven are pretty darn long....this is why I dont think this belt was from a victory bike.

.

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