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Discussion Starter #1
PRIMARY (driver or driving) CLUTCH OVERVIEW

The main purpose of the Primary Clutch is to control the engine speed throughout all shift ratios. Simply stated, it has to hold the RPM’s at the POWER(Torque) range while it changes the gear ratio. The clutch itself is comprised of many parts, however for simplicity, I will only describe the main ones.

The clutch contains 2 surfaces that the BELT rides up and down between. These are called Sheaves. One is stationery and the other is moveable. The movement these sheaves,(open or closed) and well as the movement of the belt is controlled by and dependant upon the Flyweights and Spider.

1. Fixed Sheave
2. Moveable Sheave
3. Pressure Spring
4. Flyweight (the actual weight is expressed in grams-Polaris)
5. Flyweight cam surface(spider) and roller

When the engine is running, the Primary Clutch is spinning or turning in relationshipto the RPM’s, Faster or Slower. As the RPM’s Increase (rotational speed at which the clutch is turning), centrifugal force is being applied to or created by the Flyweights and this force is transferred thru the roller and spider. This force is them being applied against the moveable sheave, forcing it to be compressed against the fixed sheave. This compressing action is what moves the belt up/down between the sheaves. Obviously there must be a method of holding or controlling this force otherwise the Flyweight would just be thrown out of the clutch. This leads me to the final key component, the Pressure Spring. The purpose of the Pressure Spring is to hold back and control the centrifugal force being created by the Flyweights revolving are a fixed point.

NOW RIGHT ABOUT NOW, YOU’RE THINKING, OK I’M LOST AND I’M NOT AN ENGINEER. Well neither am I, but I can give you a good example of what’s happening. Ever hear of David & Goliath, well if you haven’t, I not going in to that subject matter. But anyway, David was using 2 pieces of string, tied to either end of little pouch, into which he would place a rock. He would then hold the string in one hand with the rock dangling below in the pouch. He would then begin to swing the rock supported at then end of the string, ROUND and ROUND, until he had sufficient FORCE generated to release one of the strings and hurl the rock as fast and as far as possible.
The strings can be compared to the Pressure Spring and the rock is compared to the Flyweights and his Strength to spin this contraption is the Engine RPM’s. Heavier rock meant he had to exert LESS strength to make is spin faster, lighter rock meant he had to exert MORE strength to accomplish the same task. SO, heavier Flyweights require LESS RPM’s, lighter Flyweights require MORE RPM’s. The string is like the Pressure Spring, LESS spring rate is like shortening the length of the string meaning he had to exert LESS force to get it to spin, MORE spring rate is like lengthening the string meaning he had to exert MORE force to get it to spin. THIS ENDS THE LESSON BY ST.BART,YeeHaa

.After the Flyweight is thrown outward, the force generated by this action has to work against the pressure spring and some load applied the Secondary Clutch. In order to control the engine speed changes, the Flyweights and profile(the way the flyweight is designed) have to be matched to oversome the spring pressure at the right point on the shift curve.

There are 7 areas(these are described in good detail in Aeen Olvans book, to be considered in balancing the Primary Clutch system:Summarized Quotos Follow:

Free Wheeling-At engine speeds below engagement, the pretension load of the pressure spring is larger than the flyweight force

Engagement-When the sheaves engage the belt, the flyweight force is just overcoming the pretension of the pressure spring

Clutching-The clutching phase begins when the flyweight force overcomes the pretension, and lasts until the flyweights have generated enough side force to transfer the engine torque without slipping the belt

Low Acceleration-Between full engagement and the shift point, centrifugal forces are larger than the pressure spring but less than the belt pressure from the driven clutch

Shift out Point-The shift out point occurs when the flyweight force overcomes the belt pressure from the driven clutch

Straight Shift-Straight shift is obtained by matching curvature and spring rates, correct engine speed is dependent on the weight of the flyweight

Over-Run-In over-run, the clutches are shifted all the way out and the flyweight forces have no more influence on the engine speed. Engine speed will increase along the fixed high ratio line

The picture below is taken directly from the book and more or less describes the ranges in a graph fashion, which I think is pretty easy to follow.


125 Posts
Discussion Starter #2

The pressure spring is the part of the primary clutch which opposes the centrifugal force generated by the flyweights. The characteristics of the pressure spring (manufacturer & purpose) vary based upon the size of the wire, (thin,thick), (round,square), overall FREE LENGTH, and the number of coils (turns) that the spring has. Some have asked about the SPRING COLOR. Normally they are color coded, BUT, this color scheme does not always hold from vendor to vendor and sometimes a manufacture will change a part number and use the Same COLOR for a NEW Spring. This means that YOU SHOULD or MUST know the ENGAGEMENT lbs and the SHIFT OUT LOAD lbs AS WELL AS THE “FREE LENGTH”, the importance is discussed below. The Polaris service manual has a small writeup & picture indicated spring length.

Pressure springs maybe viewed as having 2 separate functions, Engagement speed and side force rate.
Each spring has 2 numbers associated with it, such as 35/215.
The 1st number is the amount of pretension lbs. that the spring has in its Installed or Compressed height The flyweight force and the speed of the engine have to overcome this pressure before the sheaves move and ENGAGEs the Belt.
The 2nd number is shift out load rate. I use my own rule of thumb subtracting the first number from the second to estimate the overall spring rate.

Springs are not always the same, due to suppliers, materials, etc. and the Free Length should be checked before installing, so that you would know if the spring gets stressed after use. This means that it sets, or holds some of its compressed form or the coils are not parallel with each other. Since the Rate is based upon give or take 1” of compression or travel, if you lost ½” free length and your normal rate was 100 lbs., NOW you only have 50 lbs. IN Plain & Simple terms, you could lose some of your Engagement and Shift Speed, equating to LOSING rather than WINNING.

LITTLE KNOWN FACTOID… There is only ABOUT 1 “ of spring compression from the Installed to the Fully Shifted out position.
ENGAGEMENT ONLY LASTS at takeoff and after that, the transmission is constantly shifting between Low Ratio and Overdrive

TUNING NOTE ----- The higher the LOAD, the MORE RPM’s or Heavier Weights are needed to Overcome the rate.
Generally for each 25 lbs of Engagment lbs, up or down, you will alter the Engagement RPM’s about 200 RPM’s
The Rate of the spring can be used to get your Holding RPM (straight shift), that is, you can use different spring rates to alter your shift curve.
The big key I believe is trying to get your straight shift at the peak Torque RPM range, then you can fiddle with the engagement. Engagement in general is a personal preference, with some liking a nice slow(rock crawl), will others want the “G” Force takeoff, fast & hard(drag racing). There are other methods of changing the Engagement RPM other than with the Pretension of the Pressure spring. Notching or Tucking, both involve grinding the weights, but we will be cover these methods in a condensed manner with the Flyweight Overview.
The Flyweight can be used to FINE Tune your RPM’s.

EXAMPLE of How to know if you have the proper spring.

Most of the Stock RZR’s will make their Pulling(Torque) Power between 5800-6000 RPM, so you would want your Straight Line RPMs to be kept in that range all the way from LowRation to OverDrive.
If you start at RIGHT ON THE BUTTON, but then the engine RPM’s drop down 500 or so RPM when you are in OverDrive(Full Shift), you ought to find a spring with about the engagement(pretension) but with a HIGHER rate. If you do this however, you’ll need to increase your Flyweights to oversome your HIGHER load in Full Shift out. Now if you’re like I used to be when I started out, WELL HECK, let’s just try some lighter weights with the same spring(PARTICULARILY SINCE WE JUST PAID WHAT WE THOUGHT WAS A SMALL FORTUNE FOR A SET OF ADJUSTABLE WEIGHTS ) N O T cause if you tried that case, you’d probably hit the REV LIMITER then perhaps settle back to the Power Range that you wanted. In addition, your engagement RPM’s would also increase, PROBABLY, causing you to hit the REV LIMITER right at Take off.
OK, lets consider the Flipside. When you Take off the RPM’s you ARE in your Power Range, BUT climb above it when you get Full Shift out. There again you go banging the REV LIMITER on the top end (if you have any topend). So what do you do, find a Pressure Spring, again with the Same ENGAGEMENT pretension, BUT with a LESS Rate, so the RPM’s will drop down in Full Shift out.

AND GUYS Believe ME, Unless YOU”VE GOT A G O O D Vendor that is willing to work with you OR you know of someone that has done this many,many,many times,
G O S L O W, or you will just give up OR go NUTTY.

125 Posts
Discussion Starter #3

Ok, let’s try somemore, if you’re not into INFORMATION OVERLOAD by now.
The purpose of your weights are to overcome the Pressure Spring AND then hopefully offset the Side Pressure being generated by the Secondary (driven) Clutch. What you gotta do is try to match the belt pressure being generated by the Secondary, so you can stay in your Peak Torque Power band. If you fail in this balancing act, the engine WILL adjust the RPM’s until its Happy, but guess what, That’s not where you want to be.
Now theres A LOT of Theory behind Flyweights, you know complex formulas, graphs, etc., which I’m NOT an engineer and if I was, I certainly wouldn’t try to explain it.
The easiest way I might attempt a little knowledge would be to say that Flyweights come with different profiles(curvature,weight placement,etc). You can see this if you looked at the different weights in the RZR from 08-10 model years. You have 20-62, 21-74,22-64 and the list goes on. Just like with the springs the weights have them numerical meanings if they are the Standard 2gm increment variety. The 1st number represents the profile of the weight(or the normal intention, such as trail riding,drag racing, etc) and has to do MORE with the SHAPE and Contour of the weight. Then 2nd number represents the weight as expressed in grams.
NOW, LIKE I”VE said before, the TYPICAL Stock setup, weights,springs,helix,etc for the Greater number of riders is A B S O L U T E LY good, matter of fact, a number of vendors have said Polaris engineers did a great job with their design. But just bear in mind, that they were forced to design & implement clutching based upon many different riding styles because one day you might be trail riding, then have to climb BIG rocks and when you get to the top, have an old fashioned DRAG race with your buddy, just cause you felt like it. NOW, it comes to you other folks that have UNIQUE needs and requirements, such as , playing in the sand dunes, mudding up to your neck in a pit,
GNCC racing, or whatever you do THE BULK OF YOUR RIDING IN.

I’m making that statement, EARLY ON, because, if you’re CLUTCHING TO MAX
For a particular riding style and the next day, you fall off the horse and try something 180o different than what you set up for, GUESS WHAT, YOU wouldn’t be a happy camper, so don’t your Vendor,your buddy that help you set it up and ABOVE all, DON’T BLAME me cause I told you what would happen. OK, SERMON’s over again.

I AM A VERY FIRM BELIEVER IN ADJUSTABLE WEIGHTS, particularly since they weren’t too plentiful when I got started. SO, if you want to TUNE, GET the
ADJUSTABLE weights and be done with it.
Due to the wide variations in MOTOR Mods, I would say that you should get a set where you BASE(starting weight) is within 8 or so grams of what you are currently running AND that when you add your additional weight, you would use about ½ of the total available additional weight. Ex. Say you are running 70 grams weight at present, the adjustables you are looking at have a Base weight of 60 grams and the ability to ADD a additional amount of weight equal to about 16 grams. These would be ideal, due to the fact, IF, you needed the Full 70gms, you would still have 6 more to play with, although that might be cutting it too close, if you’re considering increased compression or cam changes. I also would want the ability to change my weight in ALL 3 areas that affect shifting. Low, Mid, Tip, because without this capability, it’s almost like you’re stuck with the Preset 2 gram increment weights, and either have to buy another set, if you made a bad decision, OR Take a Lesson from the PRO’s and learn how to GRIND them. Your Choice not MINE, BUT, I ‘ve ALREADY told you what I would do.

A flyweight is divided basicly into 3 unique areas.
Shift Curve

For most stock weights, the engagement area is basicly just a longer shift curve, that is no noticeable difference. While the transition area is in the 1st part of the shift curve. Manuals and books that I’ve read indicate about the 1st ¼” of the shift curve.

The SHIFT Curve is the BIG Banana in my opinion, because the more curve at the end meaning that it would require LESS RPM’s to produce the same shifting force than if the Angle were not as great, meaning MORE RPM’s to produce the same shifting force.
The amount of the centrifugal force that is transmitted between the flyweight and the roller is determined by the contact angle. If you have a smaller angle, then you do not get as much force transferred.

Engagement is also controlled by the angle between the roller and the flyweight. The greater that angle, the less engagement RPM, the less of an angle means HIGHER Engagement. This is the point that I referenced in the Pressure Spring section, because you could grind a flat spot in Engagment portion of the weight and/or grind a notch in the Transition area of the weight. These 2 options Will Increase your Engagment. However, from what I’ve been told, Notching is the extreme of the 2 options.
Another method of altering your engagement is referred to as “Tucking Under”. When the center of gravity is under the pivot point, you got all the Engagement speed that you could ever want, cause you removed material from the underside of the Flyweight and now theres no arm to swing it out. This WILL make the Engagement Speed increase significantly BUT, you will probably have to RE-clutch due to the change in Shift out.

The following link is to an article written by Randy Nouis regarding the theory behind Primary Clutching. Technical YES, INFORMATIVE-YES, good pics and examples of centrifugal force determined by weight of the flyweight,radius of the center of gravity from the centerline of rotation and the square of the speed of the rotation. Now, doesn’t make you want to take a look. Kidding, really a good article, even though the end part of the article is pushing a particular brand of adjustable weights. Just never mind the sales pitch.
Theory & Mechanics of Flyweight Technology

TUNING Note….Weight Distribution has A major effect on shifting patterns. If you have more weight on the end of the Flyweight, they are usually a little softer on the Shift Out,
Tend to hold RPM’s down and be more Aggressive on the Top End. Now if the end or tip is light and you’ve got more weight in the Middle of the Flyweight, you’re likely to Rev more on the Top End AND be the Shift Out should be more aggressive.
General Rule of thumb for every 1 gram of weight, increase or decrease, you will changes your RPM’s between 100-150 RPMs. If you happen to be dealings the the 2gram increment, FIXED weights, each 2 gms change, increase or decrease, will alter the RPMS between 200-300 RPM’s
Now if you really want to get serious, you could alter the distance between the pilot pins on the clutch spider. This is accomplished by stacking of shims which would alter the shift pattern. The location of the rollers to the flyweights as discussed above earlier is critical to the shift patterns of the clutch. The distance between the flyweight pins and the shaft is fixed and can not be altered, but by shimming you are altering the starting distance between the pivot points and the shift axis. This procedure in not normally done by the average tuner but rather by racers.

TUNING Note… You should always check the rollers,pins,buttons bearings, etc for wear and friction, anytime before serious Reclutching as well as just periodic maintenance.
Also, if you’ve got it dialed in really well and have a GOOD Overall Clutch, your backshift should occur within a couple of hundred RPM’s of your Up Shift.

Again Guys, THERE LOT’s MORE, B U T it’s really outside the scope of just trying to get everyone to understand what they are dealing with. And I know this is going to sound like I’m PLUGGING his book, but really, if you’re going to do it, do it right.
Get OLAV AAEN’S Clutch Tuning Handbook, read it, and maybe you won’t have to ask any general questions and could REALLY GET Specific.

Let’s hear from EVERYONE that has got the book, just a quick YES and if you think it helped you out.

Well That’s IT, for this part, Until the NEXT One.

The Backyard Clutch Tester
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