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Clutch Mods




Put together a quick comparison between clutch modifications for those trying to understand the difference. The higher the belt comes up out of the secondary clutch, the lower the take off gear ratio. This yields greater starting torque transfer, something that generally wanted by everyone. This has nothing to do with your top speed, however your speed may be influenced depending on the modification used to get the belt to the height achieved. Stiffer secondary springs help you stay in this low ratio longer, but do not actually change your ratio. Therefore ratio must be changed through modification of the cvt system.

The first two images show belt exposure with the cvt cover in place. As you can see the Hunterworks runs at the absolute maximum belt height, just slightly below the cover (He actually uses feeler gauges to determine belt height). The more you machine the sheave, the more low end you can achieve. The bottom line; you cannot achieve lower gearing without damaging either your belt or your cvt cover. Anyone can grind metal out, proper tuning of the cvt system is key here.

Lastly is my sheave which is a highly modified version of the Hunterworks sheave, fixed sheave and secondary. Many of dunes/rock crawler drivers do not use their cvt covers in order to keep their cvt belt temperatures low and to maximize their sheave modifications well beyond the norm.

My current clutch setup lowers the cvt gear ratio 48% lower than stock. For some reference, the Hunterworks clutch is 24% lower for the rhinos and 16% lower on the Wolverines, mainly due to the cvt cover limitations. At a reduction of 48%, I have the ability to use 31" tires and still have the gear reduction of 24% over stock. I think 27's will suffice for now and I can climb up anything in high gear while still maxing out at 56mph.

For my rock crawling, the slower the better. Horsepower sells cars, but it's torque that wins races. :hihi:

Here's some interesting reading about clutch mods pre- 2010 and who originally created them.
Nyroc's ATV info website



Tinken,
From what I have read to obtain the 48% reduction from stock, I am unable to run my clutch cover. I sure could use that low end. I am a mud rider and go through a lot of water, so I need the clutch cover. I would have to make some kind of watertight modified clutch cover.

Thanks in advance,
Brian
 

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Put together a quick comparison between clutch modifications for those trying to understand the difference. The higher the belt comes up out of the secondary clutch, the lower the take off gear ratio. This yields greater starting torque transfer, something that generally wanted by everyone. This has nothing to do with your top speed, however your speed may be influenced depending on the modification used to get the belt to the height achieved. Stiffer secondary springs help you stay in this low ratio longer, but do not actually change your ratio. Therefore ratio must be changed through modification of the cvt system.

The first two images show belt exposure with the cvt cover in place. As you can see the Hunterworks runs at the absolute maximum belt height, just slightly below the cover (He actually uses feeler gauges to determine belt height). The more you machine the sheave, the more low end you can achieve. The bottom line; you cannot achieve lower gearing without damaging either your belt or your cvt cover. Anyone can grind metal out, proper tuning of the cvt system is key here.

Lastly is my sheave which is a highly modified version of the Hunterworks sheave, fixed sheave and secondary. Many of dunes/rock crawler drivers do not use their cvt covers in order to keep their cvt belt temperatures low and to maximize their sheave modifications well beyond the norm.

My current clutch setup lowers the cvt gear ratio 48% lower than stock. For some reference, the Hunterworks clutch is 24% lower for the rhinos and 16% lower on the Wolverines, mainly due to the cvt cover limitations. At a reduction of 48%, I have the ability to use 31" tires and still have the gear reduction of 24% over stock. I think 27's will suffice for now and I can climb up anything in high gear while still maxing out at 56mph.

For my rock crawling, the slower the better. Horsepower sells cars, but it's torque that wins races. :hihi:

Here's some interesting reading about clutch mods pre- 2010 and who originally created them.
Nyroc's ATV info website



Tinken,
From what I have read to obtain the 48% reduction from stock, I am unable to run my clutch cover. I sure could use that low end. I am a mud rider and go through a lot of water, so I need the clutch cover. I would have to make some kind of watertight modified clutch cover.

Thanks in advance,
Brian
That is correct, you would have to modify your cvt cover.
 

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Nyrok's Atv website and forum has changed to the point that my original list of CVT modifications has been moved and I have yet to be able to find it again. Here's some interesting reading about clutch mods and who originally created them. Keep in mind that the original article was posted prior to 2010, therefore dating many other manufactures who have falsely claimed these inventions.

I have split the post in two due to character restrictions of RhinoForums.net



Clutch mods explained - All Models
by Glenlivet, 07-25-
2010


Forum member Coop45 used his snowmobile CVT experience to develop a series of very effective mods for the King Quad CVT and the mods are called 'Coop mods' for that reason. These mods are mostly accomplished by machining and altering the King Quads clutch components' dimensions, clearances, and/or sheave face angles, to alter the CVT's shift rates and reduction ratios from those chosen by Suzuki. They allow the user to get a lower 'geared' low, or a slower rate of upshift for the first part of the range, or to reduce the gearing across the range to make up for larger tires.

As usual with end user modifications to a manufacturers design, CVT modifications involve compromise. Give something for what you gain. The manufacturer has chosen specifications that make the CVT transmission operate efficiently and to suit the needs of the broad number of their customers. The compromises arising from our CVT modification are mostly about marginally reduced gas mileage and potentially reduced belt life. In the actual event, mileage reduction isn't noticeable and the belt appears to last essentially pretty much as long as stock configuration. Go figure.



The performance of the CVT is greatly affected by the tire size. The larger the tire circumference the taller the overall gear ratio and the more difficult it becomes to achieve useable and comfortable low reduction. It's handy to refer to CVT reduction in terms of percent (%) under or over the stock configuration as supplied with the machine, and we'll use that here in this Tip.

First thing to understand with the King Quads wet clutch equipped constant tension CVT is that there are three stages the CVT transmission equipped driveline goes through from full stop to top achievable speed. The stages start start with the machine at rest and idling with the transmission selector in a gear, and then apply throttle:

1) The wet clutch shoes throw out and engage the inside of the wet clutch bell, and begin to propel the machine. As speed/RPM increase the shoes continue to slip while pressing harder against the bell until the RPM at which the shoe pressure exceeds the resistance of the bell's load and the wet clutch has 'locked up'. Depending on load this might be at around 16-20 KMH (10-13 MPH) in high range or 8-10 KMH (5-7 MPH) in low.
The lockup speed will be higher when aftermarket 'high stall speed' springs have been installed. (a phrase borrowed from the automotive high performance torque converter) Lockup is the end of stage 1, though it's actual speed depends to some degree on the load the CVT is under.
If stronger wet springs have been fitted then the CVT will have already started to upshift by the time the wet clutch locks up solid.

2) Once the wet clutch has locked up, the CVT will be operating at it's lowest reduction.(unless stronger springs are in there, as above) The front clutch is at it's widest and thus creates its smallest pulley and the rear (secondary) clutch will correspondingly be as fully closed as the belt width permits, and at its largest dimension. (The rear clutch spring acts to keep the belt tight and makes the rear clutch do the inverse of whatever the front clutch does. The rear clutch is the follower and the front clutch is the master except when slowing under engine compression when the rear clutch spring acts to push the front clutch toward opening)
As speed/RPM continue to increase the CVT begins to go through its range of operation, the roller weights travel outward in their channels in response to centrifugal* force acting on the rollers' mass, pushing against the spring pressure transmitted through the belt from the rear clutch. The rollers' outward pressure, increasing as the engine turns faster, progressively overcomes the secondary spring pressure and the CVT upshifts.
When the CVT has fully upshifted and the rollers have reached their outer limit in the clutch channels, the front clutch is as far closed as it's going to get and the rear is as open (small) as it will get. So much for stage 2.

3) After the CVT has fully shifted out, any further speed increase will be from increasing RPM until the rev limiter kicks in.
Note that if ever lighter roller weights and/or stronger secondary spring are fitted then the speed at which full upshift happens will increase, until the point that the roller weights are too light and the CVT will not even be able to fully upshift before the rev limiter is reached. After a point lighter roller weights become a very inefficient way to get more power.

* (Centripetal force, actually. For what it matters...)

The main point is that changes to the shift rate can be had with clutch kits that offer different roller weights and secondary springs, (and in the case of the EPI kit stronger wet clutch springs that raise the wet clutch slip range) but clutch kits don't affect the overall gearing. They only alter the rate of upshift within the CVT's range. They only affect the range described in stage 2 above.

Note A little grade school geometry shows that increasing tire size in the range used by ATVs, every inch larger tire diameter results in a taller final drive gear ratio of about 4%. So 27" tires make your gearing about 8% taller than it was with the stock 25" tires.
Clutch kits strive to make this up but there is nothing they can do about your starting gear ratio. No matter what weights or springs you have in there, the starting gear ratio is the same, determined by the belt position in the primary and secondary clutches with the machine at rest.
Only tire size or CVT mods can change this ratio. *

* There have been experiments with exchanging the final drive gears inside the engine cases for lower ones. Indeed the 450/500 have lower final drive gears than the 700-750 and might even be a bolt-in substitute for 700-750 final drive gears! This is of course major surgery on the King Quad and involves removing and splitting the engine crankcases.
 

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· Coop 1, or the shim mod.
The addition of shims to the front clutch collar. Very thoroughly described in Tech Tip CVT mod (Coop45 mod) - 700/750
This mod when using the full 2MM of shim, reduces the operating ratio of the CVT evenly across the range by @5%, virtually restoring stock gear ratio on a machine that has been fitted with 26" tires over the stock 25".

This is a remarkably inexpensive mod and holds the best bang for the buck for anyone looking to hop up his King and who is not afraid to do some minor monkey wrenching that is barely more involved than changing the belt.







The compromise is that the belt will now describe a tighter circle in the front clutch than it did. This does not seem to be any problem with the stock Suzuki belt or with belts of similar construction like the Carlisle UA837 but may shorten the life of belts with a thicker section such as the Dayco HP2234. (search for 'Bang' for further info)
Another thing to consider is that the shim mod causes the splined fixed plate to ride further out on the wet clutch output shaft splines and there is not an abundance of that shaft splines to start with! Due to manufacturing tolerance differences in different machines some owners find that they do not have a safe margin of spline left to engage the fixed plate when using the full 2MM of shim mod, and they have to back it off to 1.5MM or 1MM total shimming.

Owners doing this mod that have stock 25" tires will see their top speed reduced by 5% though the quads low speed technical 'rock picking' ability will be much better.
Owners with 26" tires will have about the same top speed as they had with their stock 25" tires though the speedometer, driven off the transmission as it is, will read slower than it did for the same ground speed.


· Coop 2, or fixed plate mod
Again very well described in the Tech Tip Clutch mod Coop45 's fixed plate mod - 700/750
This mod restores the top speed that can be lost as a result of the Coop 1 mod. The low reduction of the Coop 1 is retained and with the re-arcing of the fixed plate as shown, the moveable plate is once again pushed as far in as before when the rollers are at the outer extreme of their channels. This restores the lost 5% of top speed for people with 25" tires and a 2MM shim mod.
It can also permit higher top speed than stock for people who have fitted larger diameter tires, if their engines develop enough power to pull such gearing.




The machines speedometer cannot be considered an accurate measure for top speed when considering Coop mods and changed tire sizes. The speedometer drives off the engine transmission unit's gear train and it assumes a 25" tire. When larger tires are fitted, the real ground speed will be faster than the speedometer reads and given the fact that the different tire manufacturers do not make a consistent and reliable diameter for their tires stated size, you cannot even rely on mathematics to get a yardstick for your speed! A GPS with speed readout is about the only reliable standard to measure speed when you have modified tire size and you want to measure your results.

If tire size has been even modestly increased then a Coop 2 may not be needed along with a Coop 1, and can even be detrimental overkill if the engine is not then able to achieve top RPM and reach the rev limiter. It would then be over geared.
On the other hand if you can pull the gearing it might have long legs and enable the quad to loaf along open gravel roads at high speed for the RPM, and the quad might deliver better gas mileage under these conditions.




Once tires as big or bigger than 27" are fitted then the Coop 2 mod is definitely not the mod you want*, as the machine will never produce the power needed to pull that tall of gearing without both NoS and the help of a Bonneville style full fairing.
*...Unless you are a serious mudder and your goal is getting as high a potential wheel speed at top CVT ratio as you can get in low range, and you do not care about an overgeared top end in high range.
· Coop #3 (Standard, with seal protecting ridge)* (note: This mod is pretty much antique, machining mods have passed it by)
*There have been a few different ways of describing the #3 mods. I'll try to use a standard that I hope doesn't offend anyone.

The #3 is the moveable plate machined down to a depth of 2MM, at the same angle as supplied by Suzuki.

Zundappchef's drawing below shows two views of a stylized moveable sheave, as seen from the front of the machine, with angles and cut depths exaggerated for clarity.
The one in red marked 'Coop Mod 3' shows the clutch face turned down on an angle matching the original clutch face surface. This mod has exactly the same effect as the 2MM shim mod (Coop #1) but does not make the steel fixed plate ride further out on the wet clutch output shaft splines the way the shim mod does.

Compromise: The #3 mod reduces the gearing all across the CVT's range just like the shim mod. This may be exactly what the owner of a larger tire equipped machine wants, while owners of stock 25" tires would see their top speed as regulated by the RPM limiter reduced by 5% (on a 2MM cut sheave)

Note: There must be a seal protecting lip at the center of the plate for this mod and the #3.5 mod. See the description in the next article paragraph.



The collar on which the moveable clutch plate rides has a plain bearing equipped hard steel insert held in by its interference fit, a step in the bore on the roller side, and a retaining ring on the clutch face side.
There are seals press fitted onto both ends of the collar bore because the moveable plate rides to and fro on the collar and the plain bearings inside need the bit of grease inside that space, which must not be contaminated with belt dust nor the belt contaminated with grease. The seal on the clutch face side is basically flush with the clutch face. This means that the clutch face cannot be machined down all the way to the middle or this seal would lose most of its pocket and the belt when worn or when shims are employed as well, might go low enough to contact and dislodge it.

For this reason, when doing a Coop #3 or Coop #3 tapered mod the machinist must leave a ridge of aluminum from the old face dimension to support and protect the seal. (this pic courtesy TheGreenRider. The chipping damage isn't the focus of our attention) This pic shows the ridge needed to protect the seal.
If shims are added to the Coop #3 or coop #3 tapered there is the possibility that the belt may become notched on one side of the inner ribbing.
There should be plenty of belt clearance above this ridge for the belt of a Coop #3 modded clutch that does not have additional shims and has an in-spec belt. The apparent slight differences in tolerance among machines suggests that additional shimming with a Coop #3 or #3 tapered can result in contact. Not that this is the end of the world or that contact of the belt on a seal protecting ridge will result in failure, and no such belt failure has yet been reported due to a Coop #3 mod and shim, it's just something to be aware of.





· Coop #3 tapered (Shown as Coop 3.5 in the drawing) (note: This mod is pretty much antique, machining mods have passed it by)

The sheave is machined as in the Coop #3 but the angle of the moveable plates surface is increased so that while the innermost part of the clutch face is reduced by the previous 2MM, the outer extreme of the clutch face is not changed at all.
This retains the top gear ratio as it was when stock but reduces the lowest gear ratio by the amount of a full 2MM shim mod. The CVT is actually broadened in its operating range by this mod, and the ones that come after. A lower low is achieved and the top ratio is retained as before.
Good for 25"-26" tire equipped Kings so that top gear ratio (top speed) is retained while the lower low end is achieved.

The inner seal protecting ridge is retained as in the Coop #3.


· Coop #3 plus (Coop #3+) Tapered and straight (big tire)

A further development of the Coop sheave mod by Tonyjames28, in which the seals are removed and the inner hardened clutch bearing insert is pressed out and reduced in length by the machinists choice, 2.5 MM being prudent. This amount allows sufficient wall material for a the machinist to make a new ring groove.
The insert is then restored to its place and a new snap ring groove is cut that same distance (3 MM) inboard of the original. The seal is replaced 3 MM inboard of its old location and now the clutch face can be machined as either the Coop 3 Tapered or the Coop 3 (for bigger than 26" tire). No protecting lip is needed with a Coop 3+.
The clutch face is modified for its full inner range and only the collar itself now limits the innermost potential of the belt, depending on belt wear and the amount of shim chosen.

Compromise: As in all the mods above the belt will describe a smaller circle than stock. This may affect belt life and reduces the area of contact in which the motor's power is transferred to the belt. The belt has the least contact when it is transferring the most torque. At high throttle settings slippage can theoretically occur depending on secondary spring strength. (in practice, when making a big application of throttle the belt spends very little time at its innermost location, beyond the initial surge)

Pic courtesy of Tonyjames28


#6)
· Coop 4
This mod leaves the moveable clutch face alone and it involves machining on the roller side of the moveable clutch, to allow the rollers to travel further down their channels and the fixed plate to sit far enough into the roller side of the moveable plate to permit the advantage of this.


All of the Coop mods but for the #2 accomplish the same thing, at lowest reduction they allow the belt to drop further into the front clutch and to form a smaller pulley from it. This makes the rear clutch a larger pulley, though only by a small amount given the relative proportions of the clutches at this point.
The result is lower gearing at the low end in all cases, a desirable thing to have in the notoriously tall geared King Quad, especially the 700-750 models.

Several people who have access to machine shop tools and who are machinists or can get an adequately skilled machinist to do the work, have done one or more of these mods for themselves. As well, there are forum members who do the mods for a price including the author of this Tip, and they are readily found upon asking on the King Quad forum.

There are numerous other CVT machining mods including machining of the secondary sheaves, indexing of the secondary springs wrap preload, and shortening of the collar for increased top gearing, but these are outside the scope of this Tip.
- Fitting a clutch kit to make up for bigger tires

A 'clutch kit' doesn't change your low end gearing. The clutch kit only changes the RATE of the upshift within the CVT's existing range, by way of lighter roller weights and/or different strength or rotational preload of a different secondary spring. The lowest gearing in the range remains the lowest gearing in the range, determined by how small a pulley the front clutch forms at the mechanical limit of its excursion, and how big a pulley the rear clutch forms using the amount of belt the front clutch leaves it!

Now if the clutch kit also includes heavier strength wet clutch (centrifugal clutch) springs and those are installed, THEN it will make that wet clutch behave like a high stall speed torque converter in a hot rod automatic tranny equipped car or truck.

But making the engine rev higher (and be in a higher power output capable RPM) until the wet clutch shoes throw out and the clutch engages in order to get low end power, is a 'poor mans' or rather a poor engineers trick to get more power.
Would you ride the clutch so the engine revs higher in your pickup truck, in order to get more low end grunt?

The other problem is that those tighter wet springs delay engagement all the time, not just when you want it more low end grunt. This makes technical riding more touchy and less fun.

The only way to gear down the low end without gearing down the whole driveline is by machining techniques that include tapered front clutch plate machining, or machining to extend the rollers range of travel.
Then you get all kinds of low end reduction without sacrificing high speed gear ratio, and you can throw away those stronger wet springs.
Why would you want your clutch slipping and turning your power into heat as well as all that clutch shoe material contaminating your engine oil, when you can have that low end gearing anyway without the wet clutch slipping?

Some slip is necessary to get the quad underway from a stop, but slipping it to get low end gearing is not very efficient.
 

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I'm always working on new modifications and inventions with my clutches. My velocity weight set design has been really sucessful for extra smooth operation and extreme wear without the use of grease. Latest inovations include the the ability to cover velocity weights with a ceramic outer coating. This extreme pressure coating allows the addition of velocity weights to coated and non-coated sheaves. The nano particle transfer coats both metallic surfaces during normal operation. In other words, if you have previously installed a non-coated sheave, the addition of ceramic weights will allow you to obtain similar results. Obvious advantages to having both coated remains still superior, still, there are now options.
 

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I wanna go faster
 
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