Clutching - Light or Heavy Primary Spring Best

Frostbite · Nov 10, 2009

I was always taught to "load the motor" as I learned snowmobile clutching. That meant to make the engine work (struggle possibly) to pull shift speed RPM. I did this with great success on my past sleds.

To add another factor to the primary clutching equation, I found that using the highest total force spring available allowed me to throw more weight (through my clutch weights) at my primary clutch and engine. This of course made the engine work even harder to pull top RPM because my primary weights had to be very heavy to keep from over reving with high total force springs.

I ended up sticking with the highest total force primary spring available and used it as a constant. I also learned a couple of things when I started playing around with clutch weights.

1. Heavy clutch weights seem to make the sled less snappy (rightfully so)because the engine has to work so hard to overcome all that weight. Lighter clutch weights seem to make my sleds feel much more snappy and dirt bike like.

2. Heavy clutch weights that can be pulled easily by a sled at lower elevations become insurmountable for the engine to pull as the elevation increases.

My question is: Is a sled able to reach it's full power potential when a primary spring of less than high total force is used?

If a lower total force spring is used, lighter weights consequently have to be used and the motor isn't being loaded as hard as it could be if one was using a higher total force primary spring.

The reason I ask is, my SLP Performance Edition Kit came with a primary spring with a rating of 160/310. I also see SLP makes a primary spring that is a 160/340. If I apply the above theory, I could theoretically throw more weight at the primary (and load the motor harder) potentially pulling a few more horsepower out of the motor if I used the higher total force spring.

What do you guys think?

Arctic Thunder · Nov 10, 2009

I always looked at it as a balancing act. Either heavy weights, stiff spring or light weights light spring.

IMO I like the snappy feel. So I prefer the lighter weights and lighter finish rate spring. Also I always felt there was a lot more clutch wear with the heavy weights, so again I tried to stay with lighter weights.

Just my opinion. Probably left a lot on the table in this area.

Again this is an opinion. I think drag racers like the heavy weights. When you nail it and it pulls HARD and you hold it throughout the run that is great and what you want. But when you are a boondocker, mountain rider you need to have the snappy, get'r done now response.

Thunder

Schags · Nov 10, 2009

If you put a heavier spring in the primary, you need more weight to overcome it, how is this different from a lighter spring with lighter weights? How would this load the motor more? I think the relation of the primary too the secondary is the way to load the motor? A steeper helix, or a lighter sec spring, or heavier weights in the primary with the lighter spring should make the engine load up more... Right?

Frostbite · Nov 10, 2009

Yes, you can load the motor through your secondary via a steeper helix but, I was always told to tune your shift speed with the primary clutch setup and fine tune for conditions via the secondary.

Yes, drag racers would want heavy primary weights to accelerate as hard as possible, most likely with very little regard to throttle response and flickability.

Yes again, we as boondockers are probably much better served with light weights and springs in the primary clutch.

I guess my question really should have been:

Are we leaving untapped performance on the table when we chose to use lightweight springs and weights in the primary?

Schags · Nov 10, 2009

Thanks for confirming, really new to clutching myself. But Ive heard to set the rpm with the primary and shift with the secondary. The secondary has more influence on the primary than vice versa, one thing gets me thinking, alot of people are seeming to blow belts when punished when using a shallower helix, with these high hp sleds, won't all that torque going to the secondary make the helix create lots of side pressure, keeping the clutches from shifting up thereby not loading up the engine, causing the primary to slip?

Frostbite · Nov 10, 2009

That could be or............ the shallow angle helix and a low tension secondary spring is letting the secondary shift out too quickly or perhaps too far, allowing the belt to crawl too far up the secondary clutch for the its own longevity?

mrquick68 · Nov 10, 2009

FYI - SLP Measures their spring different than cat does. so don't compare the AC spring rates to the SLP rates - SLPs appear to be stiffer than they are.

And to answer your question - i've never liked the stiff spring heavy weight combos, i always perferred the shifting patterns of the medium weights with softer starting spring, with average finishes.

as for helix's, best one i ever ran on a M sled was one i had Dalton custom cut for me - 44/41-37. worked killer. My little M7 was always pulling 43 to 46mph track speeds with that setup. Pretty awesome.

ItDoAble · Nov 10, 2009

FYI .. keep in mind that SLP measures their springs at different distances than OEM AC. So a SLP 160 may be equivelent to a ~150 AC, and the SLP 310 finish would equate to ~295 AC.

SLP 160/310 is very close to the AC org/wht, only ~10 lbs heavier across a linear graph (which of course is not a perfect measure of rate).

Here are a few springs graphed (linear).

longrider · Nov 10, 2009

clutching

I'm getten dizzy

Schags · Nov 10, 2009

Frostbite said:
That could be or............ the shallow angle helix and a low tension secondary spring is letting the secondary shift out too quickly or perhaps too far, allowing the belt to crawl too far up the secondary clutch for the its own longevity?

Do you mean steeper? 36 is shallow compared to a 40 right? If that happened would it not load up to much and drag rpm's down?

Griff · Nov 10, 2009

Lots of questions posed and variables mentioned here. You can zero in on a good clutch set up with the help available on the forum. You can also expand your knowledge by picking up Olav Aaen's Clutch Tuning Handbook.

Griff · Nov 10, 2009

ItDoAble-

Your graphs are extremely helpful. Are they plotted from bench testing or manufacturer specs?

Thanks.

ItDoAble · Nov 10, 2009

Griff said:
ItDoAble-

Your graphs are extremely helpful. Are they plotted from bench testing or manufacturer specs?

Thanks.

Linear from Mfg specs.

Like to do some bench testing, though

But with my luck, I'd start testing after too many :beer;:beer;:beer;:beer;:beer;:beer; and regret it later

iluv2fly · Nov 10, 2009

With my slp performance edition kit I run the 160/310 spring and 74G MTX weights with no rivets and a 44/36 helix in the secondary. I ride 6-10K and the setup runs awesome! SLP has done a lot of testing with the performance edition kit, I would trust there setup as it works awesome on mine.

swnhrt · Nov 11, 2009

Spring force is linear. The shift force from the cams is/are exponential. The spring force has minimal effect at full shiftout. The primary purpose of the spring is to set engagement rpm... Hope that helps!

Frostbite · Nov 11, 2009

Swnhrt, thank you but the primary spring had multiple functions.

One being clutch engagement (preload). The higher the preload of the primary spring the higher the clutch engagement RPM. I sometimes use spring shims at times to bump up the engagement even more.

The second being total force. One way your shift speed can be adjusted is by changing the total force rate of your primary spring. Higher total force springs require more clutch weight to fully compress them. So, if you use your same primary weights with a higher total force spring, your shift speed goes up accordingly.

I know primary spring shims are made to be used to increase engagement RPM but, I have found they also bump up the total force rate a tad bit, so in the past I have been able to add even more primary clutch weight before reaching my target shift speed.

The shift rate is yet another facet of primary springs. How fast your sled is allowed to shift up is controlled by the spring rate of the primary spring. The higher the rate the slower the shift up. Typically this is controlled by the spring gauge wire diameter, thicker spings equal slower upshifts (with exceptions).

Hope that helps! :beer;

skidooboy · Nov 11, 2009

it's really a give and take. talking in the primary clutch... heavy springs raise rpms, light springs lower rpms. if you have too much spring you can reduce the spring rate, and or add weight the primary arms to reach the desired rpm range. if the if you have too weak of a spring, you can up the spring force, and or lighten the primary arms to reach the desired rpm range.

my theory is, if you are really close on rpms, i dont mess with the arm weights, i adjust with a weaker spring for a slight over rev condition. or stiffer spring for slight under rev condition.

if you tune rpms with the secondary you are giving up shift characteristics somewhere in the power curve. ie: robbing peter to pay paul. so somewhere in the curve you gain and somewhere you will lose. you have to ask yourself, is that acceptable to you.

easy rule of thumb to remember... tune rpms with primary, tune the upshift and backshift with the secondary.

it is a fine art, and you can never learn it all. buy a bunch of springs, weights, helix's and go have some fun. just remember to use a guage, either another sled you dont touch (mule), or some sort of timing, telemetry that you can look at and duplicate. radar gun. measured distance and rpm/speedo readings ect... then you will know if you gained or lost and can adjust from there.

as temp, elevation, snow conditions change so does your optimal clutching. again, goes back to the top, it is a give and take. AND it is a labor of love. BUT, when you do it yourself, and find the "sweet spot" it is that much more rewarding to yourself. ski

Frostbite · Nov 11, 2009

Ski, I agree that once you find the sweet spot it's very rewarding.

You'd be shocked to see all the springs and clutch weights I have tried. I now know what works FOR YAMAHAS but, I'm still trying to figure this Cat thing out. I found the Orange/Silver/Orange Yamaha's most stout primary spring to work the best for just about all of my applications. So, that became my tunning constant, having a constant really starts to simplify the rest of the clutching. Then I found the Yamaha Silver secondary spring to work the best and I was down to messing with roller sizes and clutch weight profiles. Then I found that 15mm rollers worked the best for me and then I played clutch weight profiles and weights. I went to heavy hitters and adjusted them to pull hard on the bottom and still allow me to pull my shift speed on top. Then I could pull my shift speed at lower elevations and not up high and using the shockwave adjustable helix made everything fall into place.

Can you say aaaaaaahhhhhhh...................:beer;

I'm just not there yet with the Cat clutching.

skidooboy · Nov 11, 2009

^^^^^ you and me both brother. spent the last 10 years with yamaha's sxR's, srx, vipers, fx nytros, stock, modded, custom. learned alot from alot of great tuners, srxsrule, ulmer, ect.....

now i have to start the learning curve over with the cats. at least i have a good idea of the theory. now i just have to learn what the 800 likes and doesnt. hoping the baseline isnt too far off. i'll watch guys like yourself, and rickM and the like, having similar tastes and mods that i have. and have those thoughts help me find my high elevation set ups. the low elevation will take care of itself. (i hope)

keep up the good work.

ski

trencher · Nov 11, 2009

I agree with a lot of all of what most have said. This is my take. I've ran cats my hole life. The primary is to set your rpm & secondary the rait of shift. So i don't like my sled to slam in. So i have a low first # on my primary spring like 125lb. Then i like it to pull hard so i like to use as heavy weights as possible to crowd the secondary harder. So i use a high second # like 340. SLP make a great selection of springs. Cat makes a great weight. So does slp i ran the mtx in my 1000 they work great if you have time & are persistant.The shift rait changes alot between the end hole & the middle hole.The middle hole will relieve the secondary & the the end hole lodes it. It's a trick to find the right combo.A 42 34 helix might be a good one to tri.Get a shift assits from Black diamond exteme & change your seondary to run the m7 helix's then you need a seondary spring from Goodwin Performance.Blue white. Dalton industries has the best selection of helix's.
Happy tuning it a life of SMALL ONE AT A TIME AJUSTMENTS. The m8's are light on weight from the factory.

Clutching - Light or Heavy Primary Spring Best

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