There seems to be a lot of questions concerning primary springs in the forums. I have touched on this before but this time I will try to write a more in depth article about the primary spring and what its job is in the CVT system and how the Primary "front" pulley works. This is mainly written for a Prairie 650 but the concept can be applied to any ATV using the P650 belt design.

First of all I am by no means a clutch expert but everything I know was learned by trial and error and taught by Dale Toole, aka Helix, owner of Dalton Industries. A tach is needed to accurately know whats going on with your springs and anything else you do. If you dont have a tach you will just have to use your "seat of the pants method".

To start with, a CVT is made up of four different changeable component. A belt, Flyweights, secondary "rear" spring and a primary "front" spring. All of these components must work together to obtain maximum horsepower from your engine in an efficient mannor. This article will concentrate on the "front" primary spring.

The primary springs main objective is to work with the flyweights to hold the peak producing HP through out the shift curve. The ideal shift curve between low and high ratio is "straight". This means that the engine speed "rpm" is held constant at the maximum producing HP level while the clutches are shifting out to increase your speed.

To help understand this I will discuss "low ratio acceleration" first.

When the sheaves first grip the belt you start to move in low ratio. The engine speed will continue to increase as if you were in low gear in your car. While the atv speed "mph" is increasing the belt still remains in low ratio at the bottom of the front pulley. The belt will not start to move out until the flyweight force has become great enough to overcome both the primary spring and side pressure of the belt in the secondary pulley. When the engine speed "rpms" has built up enough the centrifugal force, it will overcome the primary spring and the belt will then start to move up the sheaves and the ratio starts to change. This is called the "shift point" and should coincide with the peak HP of the engine. This is ideally where you want to see 6500 rpms on a stock P650.

Next comes the "shift out point".

Like mentioned above, the ideal shift out point should be at the maximum HP range produced by your engine. A stock P650 produces 42 hp at 6500 rpms according to the shop manual. This is where you want the rpms to be when the belt starts moving up the primary sheaves. This is what the primary spring will help do along with the flyweights. So, the engine speed "rpm" and the shift curve <--"going from low ratio to high ratio", should coincide or "happen at the same time".

Next comes the "shift curve".

Remember the ideal shift curve is "straight" between low and high ratio. Straight, meaning the rpms stay the same while the mph increases. So, you want to hold 6500 rpms at all times while the belt is moving up the primary "front" pulley as far as the belt will ride. The belt may or may not reach the top of the front pulley, either it could be already maxed out as far as it can travel or the belt may have some more to travel but the engine wont get it there. This is where springs "can" play a roll in helping acceleration and top end speed.

The next thing is "over drive".

This occurs after the belt has reached its highest possible point on the front pulley. Again, either it be by the belt reaching its limit and cannot go any further or the engine only strong enough to get it so far. While in over drive your rpms can increase or decrease believe it or not. Lets start again, you still want your P650 to hold 6500 rpms from low ratio to over drive now. If you are reving higher than that in over drive you need a spring with lower shift out rate. This is why a long time ago with the Dalton Blue I hit 8100 rpms but my top speed was slower. I never could understand that until I talked with Dale aka Helix. If you are way over reving in over drive you "should" need a spring with less rate "lbs". Thats why I ended up using the Plain/white spring after the spring test were over and the fact that I liked its engagement rate. This part has always been hard for me to understand but maybe our retarded stock CDI has something to do with this over rev business.

During the spring test done in September 2003, the ideal rpms were reached in 300'. I did an all spring average of rpms vs speed at each distance and got the following; 6558 rpms/ 45.7 mph @ 300', 7367.5 rpms/ 53.5 mph @600', and 7578.5 rpms/ 55.4 mph @875'. As you can clearly see the most speed was gained from the start to 300'. It took another 575' just to gain roughly 10 more mph but the rpms increased over 1000. I realize that the stock cdi was responsible for some of the deteriorating speed vs distance with its timing retard. I would love to do another spring test with my Dyna CDI + 4 degree key somewhere on asphalt.


When you make modifications to your atv the needs of the springs "can" change. This is why you see clutch kits that are sold, advertising "this kit is for stock motors with stock exhaust". Those people, "Dalton and EPI" know what maximum HP is for that particular atv and the spring kit they put together should coincide with that atv.

I hope this is easy to understand. I have been working on the wording for a long time trying to get it in the right order. Comments, feedback and question are welcome and encouraged.

Dale, aka Helix, if you read this and any part of the clutching phase is wrong please let me know so I can correct it.

Enjoy

KOD.

 

Thanks for taking the time to write all that down. You answered many questions for me. I enjoy your posts.

 

kissofdeath great article!! It definitely helped clearify clutch operation for me. thanks for the good post.

 

Good to hear from you again.

I emailed Dale about spring performance at 7000' or above and he said he didn't have any test data for high altitude and couldn't help me out on that issue.

Have you heard any rule-of-thumb that coould apply to your data regarding high altitude?

A friend and I are just going to get some springs, go up to 7 or 8k and start testing them. Since you've done all that research, what would you be looking for? Just a short answer would be ok, since you've worked on this topic so long already. By the way, we mostly just do trail rides, not racing.

 

Another great post KOD!! Its time to get a tach. Ive been using the orange/blue for quite a while but after some headwork and cams I think its time to change a little. Im getting real hard take offs to where I cant keep the front down if I lay on the bars in 2wd or 4wd, but I seem to be lacking in mid range power. My brother has a Vforce and when we race I jump ahead, he catches me in the mid range, and we top out about the same.

Since I dont have a tach I cant really tell whats happening. If you wanted to lose a little acceleration but gain in the mid range and top end what would you suggest? I still have a plain/white I was planning on trying this weekend, but before I get the tach which direction would you go?

 

wow... I am always impressed with the Kawi folk. They know thier stuff.

Thanks KOD

 

Thanks oolddog, dakotaprairie and revilo for the comments. Clutching is tricky can can only be figured out with testing, a good tach and someone to help is neccessary I think.

Plus, your Prairie, Brute Force, Arctic Cat, Twin Peaks or even a Polaris may be producing more power at a different rpm level... say 7000 rpms. To anyone wanting to get a tach and accuratly test I would say 6500 to 7000 rpms is the heart of the power/torque. Thats just something to shoot for.

kawiyowee, I havent rode at that high of and altitiude either. But, according to the shop manual, kawi offers a high altitude kit. The kit includes reduced main jets "AND" spacers for the primary spring. Forget the jets for a minute and lets talk about the spacers. Im not 100% sure but I believe the reason for the spacers is to raise engagement. I know thats what the spacers do, but the reasoning behind it I think is to help compensate for the lack of power the engine produces at that altitiude. The oxygen level will be much less and thats also why the reduced main jets are in the kit. With reduced oxygen and fuel the power will be less. Instead of changing the spring the kit just includes spacers. The spacers force the engine rpms to increase, this in turn helps the atv get started moving easier, again, to compensate for lack of power at that altitude.

Sorry to write a book about it but I feel I cant just say, "get a spring with higher engagement" without explaining why if I know why. The Dalton Plain/white spring engages my P650 at around 1750 rpms compared to stock spring of 1270. The Dalton Blue engages around 1600 for comparisons.

Rivermud, we have very similar P650s. You have two things I dont have but want to get. Where did you get the Hotcams and how much were they? Same goes for the head work? Im guessing you did them both at the same time. Could you approximate how much that helped? An answer like, " my brother's vforce could beat me by two atv lenghts at 300' now we are even" kinda answer. You know, something I can relate to.

I liked the Plain/white but when I got the Dyna in I felt it could take advantage of the higher shift rate the O/B had in the midrange so I tried it. I know it pulled really hard. For example, before installing the cdi and O/B spring I raced an equivilant P650 at 300' and we were pretty much even. After just installing the "old prototype" dynatek cdi, with the o/b spring I had increased to an atv length ahead of that same P650 at that same distance. I also did the clutch mod at this time but not sure if it was a factor at that distance.

The proto type cdi was the one Sgt Rock had and tested. It does have starter kickback. I use the pull rope to get around that issue. [img]i/expressions/face-icon-small-happy.gif[/img]

 

KOD, I did the heads and cams at the same time and was a little disappointed at first. It didnt really seem to give me the gains I expected even though I had to go up drasticly on the jetting. Last weekend I found the problem though. I wasnt getting enough air. In racing my brothers V I was loosing by 1.5 quad lengths. Just for the hell of it I took the front radiator cap access cover off and actually felt a difference. The next few races I was consitantly beside him. (but running lean)

I am now working on a dual ram air setup that I have high hopes for. my jetting was at 138/132 (DJ) but now Im switching to keihin mains with the new setup and expect to be in the 158/155 range.

With your cold air mod you shouldnt have this problem and I think it is worth the money. To answer your question, without the heads and cams I was loosing by about 1.5 quads in 300 ft with stock tires, now I am right beside him with type 5s and ATRs, and when dialed in I fully expect to win by 1.5 and be faster on the top end. (I will give the results Saturday) his Vforce is 100% stock.

I purchased my hotcams from Art at precision power sports (636) 461-0880 for $300 no core charge. The headwork was done localy at a performance shop for $150 (he charges $50 an hour for anything he does and it took about 3 hours.)

 

i was just looking at the hi lifter dyno runs and it says the 650 with the modual muffler and jet kit make 33 hp it also says that stock it makes 31.8 hp
so i dont understand how you got 42hp stock.
unless thats flywheel hp not rear wheel hp.
im not trying to start somthing i would just like to know what book you got those specs from and if its rear wheel hp or fly wheel hp.

 

that is correct, the Prairie is rated at 42hp at the crank and the hilifter dyno runs were done on a dynojet rear wheel hp. The diference is lost in the drivetrain.