Clutch/Contra Spring Ratings

[90GTVert]

I have always known clutch and contra spring ratings as RPM. 1000RPM, 1500RPM, and 2000RPM being the most common examples. I saw a member of another forum posting that they were actually measured in Newtons. I wanted to see what you guys think or if anyone has documentation to prove either way.

First off, clutch springs make my argument work. A set of 1000RPM clutch springs, by my definition, is intended to raise the clutch engagement RPM by 1000RPM over the stock springs. Installing multiple spring sets and checking RPM shows me that my way of thought holds pretty true there. You certainly can't expect exactly 1000, 1500, or 2000RPM changes... but the increase in RPM seems close enough to their ratings that it makes sense to me.

My next argument for my case is this. Wouldn't it be odd if every type of scooter engine... GY6 50, GY6 150, 1E40QMB, Piaggio, etc... required the exact same amount of force to operate in a similar fashion? Maybe I'm wrong here, but it would just seem odd that every CVT'd engine would respond well and be upgraded by 1000, 1500, and 2000 Newton springs in the clutch and rear pulley.

And finally... it just sounds like a lot of force to me. 2000 Newtons is roughly 450ft-lbs of force. 2000RPM contra springs are pretty rough, but I can't imagine being able to open the rear pulley by hand if they were truly that strong. It's also kinda hard to believe that the force generated by say 40 grams (.09lbs) of roller weights spinning would counteract 450ft-lbs of force holding the rear pulley closed. Then again, I've never had a physics class and don't know the formula for determining such things.

I may be way off. I'm just trying to make sure I'm not mis-informed and mis-informing others.

[preytheweak]

I can tell you one thing though. I've have three 2000RPM. From three different companies and they are noticeable not the same. All are stiffer than the stock spring. Of course I'm talking about the torque spring.

E-Ton stock. 6g wt. Opens to high gear at 15MPH.
NCY 2000RPM. 6g wt. Opens to high gear at 18MPH
MRP 2000RPM. 6g wt. Opens to high gear at 20MPH
Koso 2000RPM. 6g wt. Very slow to open fully. Above 25MPH it keeps the same RPMs all the way past 55 MPH+. I have not gone faster but is still pulling strong. With the RPM staying the same. I'm close to the perfect roller wt. for this spring.

As far as clutch springs go it all depends on the wt. Of the clutch pads/fingers. 2000 in mine is not the same as in a stock clutch for mine is lighter than stock.

[90GTVert]

Well, there's another problem with scooter tuning... inconsistency in both the scooters and the aftermarket.

[porzie]

WHAT SPRING SHOULD I PUT ON NOW? BAD VIBRATIONS.
I bought 2 new Sym Fiddle gy6 Scooters.
Both as new have a " belt slap " backlash of the CVT belt that hits and skids against the metal casing.
This only happens from 40kmhb to 60kmh range.
This causes a vibration throughout the scooters.
I assume the stock clutch spring is about
800rpm to 1000rpm rating.

What spring should I try next to get rid of this belt slap vibration problem?
1500 RPM?
2000 RPM?

[aeroxbud]

I buy my contra springs from polini. They are measured in kg, and increase stiffness. So 10%(22kg), +40%(28kg) or +87%(37kg) increase. Polini actually prints the kilogram force on each spring.
Clutch springs are thickness and percent increase also. 🙈
As I've got loads of clutch work from different manufacturers. It's much easier to measure thickness to gauge how strong they are. Difference in colours from manufacturers also makes it hard to know what's what.

[FrankenMech]

As usual terminology is a problem and this is a very old thread from back in 2010.

Clutch springs are the small springs that retain the clutch pads inside the clutch bell or housing. They determine the RPM that the clutch pads start gripping the clutch bell. The RPM that the clutch engages also depends upon the mass of the clutch pads and their attachment arms as well as the distance they must move to engage the clutch bell or housing. As the clutch wears the distance the clutch pads must move changes and therefore the engagement RPM changes. Clutch springs should be expressed as Newtons or their spring constant. The spring constant represents the stiffness of a spring or an elastic material. It is symbolized by k and has an SI unit of newton per meter (N/m). The larger the value of k, the stiffer the spring is and the larger the force needed to compress or stretch it in this case.

The contra spring, sometimes also called the torque spring, is the spring that controls the spread of the rear pulley when acted upon by the spinning weights in the front variator pulley through the belt. The contra spring has a certain force applied at a particular assembled height sometimes expressed in pounds or kilograms. This will vary depending on the brand of parts used in the rear pulley assembly. The force will vary due to the spring constant of the contra spring. Again the spring constant represents the stiffness of a spring or an elastic material. It is symbolized by k and has an SI unit of newton per meter (N/m). The larger the value of k, the stiffer the spring is and the larger the force needed to compress (in this case), or stretch it. I believe the name 'torque spring' is a misnomer and should not be used.

-Just my

[porzie]

Apr 26, 2024 5:08:39 GMT -5 aeroxbud said:

I buy my contra springs from polini. They are measured in kg, and increase stiffness. So 10%(22kg), +40%(28kg) or +87%(37kg) increase. Polini actually prints the kilogram force on each spring.
Clutch springs are thickness and percent increase also. 🙈
As I've got loads of clutch work from different manufacturers. It's much easier to measure thickness to gauge how strong they are. Difference in colours from manufacturers also makes it hard to know what's what.

Thanks.
It sound like the force that you excerpt on the contra to squash it flat on a human weigh scale will give you the kg reading. Im hoping that a stiffer higher rpm or kg contra and clutch springs will stop the problem of the 40-60kmh belt slapping?

[90GTVert]

Apr 27, 2024 9:22:18 GMT -5 porzie said:

It sound like the force that you excerpt on the contra to squash it flat on a human weigh scale will give you the kg reading.

I made up a spring base and flat steel piece to go in a chuck. Put the spring base on a scale and use a drill press to push down on it. Height of the spring base can be made to whatever you wish to check at and used as a stop. You have to be careful not to push against it any more than required to reach the stop though, or readings will be high. Not likely to match readings of manufacturers, but you can tell what springs in a mixed batch are actually stiffer for sure and use that to check used springs to see if they match new numbers.

Not sure if they are still around, but at one point there were spring checkers made for this. I think I saw it on an ATV racing site. There are definitely other spring checkers around, you'd just have to figure out what fits this application.



EDIT: Added some pics.

Here's one of the first times I did it. Bolts were used as stops for installed and compressed heights.
















I made the base later.

[FrankenMech]

Very good! The height at which the spring is checked is VERY important and must match the application or the manufacturers specification. The spring constant k can be calculated from those heights.

That test fixture is good to prevent 'flying springs' LOL

Unfortunately for the job of tuning a CVT these measurements are largely useless and are only important to the manufacturer for quality control -if they really do any.

For the newbie: 'Belt slap' is probably due to a belt that is too long for the application.