Adjustable Primary weights

[SledFreak]

OK, Coming off a ski-doo when I a had to adjust RPM on my ski-doo all I did was add or remove weight from the Primary clutch. Very easy on the TRA, just add set screws to the adjustable weight to achieve the desired RPM? On the Yamaha weights, there are three holes. One on the shoulder, middle and Tip. ie. If I wanted to lower my Max RPM at a full shift from 10,850 to 10,700, how would I go about figuring out how to do it? Do I add weight on the shoulder, middle or tip and why? I'm not sure how these adjustable weights work? Can any one please explain?


Thanks,



Andy

 

[BADSLED]

Full shift would be your tip rivit. Add about 1gr.

 

[SledFreak]

Thanks, but how does the adjustable weight work exactly on the Yamaha? What does each hole on the weight do?

 

[HAMMER]

Is Clutching Magic?

Not really!

Olav Aaen's Clutch Tuning Handbook is the bible of clutch set-up. If you don't already have a copy, get one, read it, put it under your pillow at night, take it to the can with you, read it, read it, read it.

Even though the clutches appear to be pretty simple, they can make a perfectly sane man sound like a babbling idiot, muttering things to himself like, wait a minute I added weight and....No, if I increase the spring rate and.....No if I.... DAMNIT !!!!! The basic idea of clutch tuning is to get the springs and flyweights in your primary (drive) clutch to bring the engine to a specific rpm PEAK using different weight and spring combinations. These combinations are endless that's why no one person has all the answers for every condition.

Then adjust the spring tension and helix ramp angles on the secondary (driven) clutch to get the shift-out you want. These combinations are also endless. The shift "characteristic" is dependent on your personal preference and riding style. The theoretical "ideal" is a slight over peak at engagement, then flat at the peak HP out all the way though the shift-out with the rpm slowly climbing above the peak HP once you're shifted all the way out. Remember that's theoretical. The point of this being that generalizing clutch settings is impossible.

Even if I tell you exactly what I run in my sled, it's no guarantee it will work for you. Most tuners won't give away their "trick" clutch setups that cost them dearly in lost hours of sleep, endless parts runs and tuning rides, but they may be able to point you in the right direction. Clutch tuning is the one area where you can gain a competitive advantage.

Where do I start?

Focus on the primary and getting your engine rpm right. That means right at PEAK HP with steady acceleration. You'll increase or decrease the weight and or profile (where the weight is distributed in the weight itself: heel, mid, tip) of the flyweights to achieve this. Lighter weights raises the rpm heavier weights lower it. Heel = bottom end, Middle = Mid-range, and Tip = top end. Make sure you're using the same profile of weight when you make changes or you'll end up chasing your tail. Do NOT change the secondary to adjust engine rpm.

I've seen too many people increase the pre-tension on their secondary to bring up their engine rpm, myself included. You are shooting yourself in the foot !!!! It decreases the efficiency of transmission of power to the track while adversely affecting the ability of the secondary to keep the shift curve flat. Once you have your rpm where you want it, you next job is to get it to shift out the way you want. That's the job of the secondary. The combination of spring and helix is what determines this. Multi-angle is what I prefer. The secondary spring directly equates to side-force on the belt.

The idea is that, the more side-force you have on the belt, the less efficient it is because of belt drag. Secondary pre-tension (wind) should be around 16-24ftlbs. What I try to do is get to the minimum side-force possible without slipping the belt in the secondary. Too much side-force and the clutch will back-shift too fast and put you in too low of a ratio and over rev when you stab the throttle out of a corner. Too little and it won't back-shift fast enough and it will react sluggishly (bog) and you'll loose rpm climbing hills or trying to maintain high speeds.

Lastly, I'm a believer in lower gearing in mountain conditions, its less work for the clutches and the engine, they will run cooler. The factories gear sleds for speeds higher than the sled will reach in "normal" conditions.

Common Pit-Falls:

Clutches MUST be clean. Bushings MUST be serviceable. Belt MUST be cleaned before break-in. Only change ONE thing at a time. Take good notes, like snow condition, temp, elevation, terrain, what you changed and the effect it had. The primary (drive) and the secondary (driven) will directly effect each other, try not to over compensate one to "fix" the other, it's a BALANCE you're looking for.

Remember, what works for hill climbing will not work for drag racing and vise versa.

Under target rpm.
1. Too heavy primary (drive) weights.
2. Too steep secondary (driven) helix angle.
3. Too low tension in secondary (driven) clutch.
4. Too tall gearing.

Over target rpm.
1. Too light of primary (drive) weights.
2. Too high tension in secondary (driven) clutch.
3. Too shallow secondary (driven) helix angle.
4. Too low gearing.

 

[SledFreak]

Thanks, that helps alot....

 

[TurboJamie]

Sledfreak I was in your same boat when I started. I know the doo clutches pretty well inside out this is totally new to me on the yamaha. If you want to reduce your RPM's you need to get the clutch rivets to add weight. Go to your dealer they should have em and sell em for like .25c each. Take your ramps out and put the weight in the tip and then mushroom the end over to hold the rivet in. You will need a gram scale to properly balance the weights because they will be to heavy. With my SC I run 74.5g of weight in the arm. I have to put a rivet in the tip then grind it down to get my weight.

Here is what I have learned from this site and playing with my own yamaha clutches. First off they are not nearly as true in machining as the doo ones but I have gotten mine alot closer. The primary mostly controls RPM and the secondary controls the shift so if you want to upshift faster play with the secondary if you need to adjust rpm play with the primary. Im not much help otherwise as Im still learning myself.

 

[Bodacious]

If I'm not incorrect I think that the 82g arms already have a 4.5 rivet in all three holes. Yes, you would want to add more tip weight to drop your top shift out RPM.... but the 4.5 rivits are as heavy as Yamaha offers, that being said I believe that an aftermarket Yammi Perf outlet may have them available for you. A 5.5 or 6g may be the ticket in the tip. The other option would be to back off your secondary 10degrees and try that. Hope this helps.