Clutching theory

[devilrmk]

Tell us what you know about clutching. Keep it to theory not what particular setup works with one sled. You can do that in the respective brand category.

[KWB]

Its been a while since I had to put this to generic terms but here it is from memory and I might have something backwards somwhere but in the interest of building the knowlege base....

Spring preload in the primary - lower load lower engagement
Total force in primary spring - how fast the shifting happens as you come off the throttle
More Weight - all things equal will bring the r's down, if you don't need to add more weight after motor mods then you didn't change the Top HP. Change to a higher total force spring and you will need to counteract it with a heavier weight
More preload in secondary wind - faster backshift but will typically generate more heat than is necessary if you have to wind it up too far.
Softer Belts need less weight.
If you don't scrub off a sharpie mark all the way out on your clutch sheaths during a day of typical riding then you should gear lower and get full range of clutch ratios.

[sledheadd]

clean clutches work better than dirty one's in theory

[Bushman]

Not really! First draw a large pentagram on the floor around your sled, get some candles and a virgin to sacrifice, no-no that would be a waste. Anyway, 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…. DAMN IT !!!!! 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 into overdrive .75:1. 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 low gearing, its less work for the clutches and engine they will run cooler. Most sled heads don’t realize that the factory gears sleds for speeds higher that the sled will ever reach. They never reach a true .75:1 ratio, also the track and engine combinations the owners and after-marketers add, won’t allow the motor to pull the tall gearing (pulls the rpm down on a long climb or high speed).

Common Pit-Falls: Clutches MUST be clean. Bushings MUST be serviceable. Springs MUST be replaced annually. Belt MUST be cleaned before break-in and every other ride (preferably) and within minimum width tolerance. If all of the following are complied with, see below. 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.

Note: Remember, what works for boon docking will not work for drag racing and vise versa.

Under target rpm.

Too heavy primary (drive) weights.
Too steep secondary (driven) helix angle.
Too low tension in secondary (driven) clutch.
Too tall gearing.
Over target rpm.

Too light of primary (drive) weights.
Too high tension in secondary (driven) clutch.
Too shallow secondary (driven) helix angle.
Too low gearing.

[irondave86]

X 2 on Olav Aaens clutch tuning handbook. It is defiantly a must read.

[smwizzz]

Nice job at explaining. Clutching is probly the hardest thing to learn and even harder to teach. Olaf's book is a wicked good book. Anyone need help clutching??? listen to this guy!!!

Originally Posted by Bushman

Not really! First draw a large pentagram on the floor around your sled, get some candles and a virgin to sacrifice, no-no that would be a waste. Anyway, 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…. DAMN IT !!!!! 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 into overdrive .75:1. 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 low gearing, its less work for the clutches and engine they will run cooler. Most sled heads don’t realize that the factory gears sleds for speeds higher that the sled will ever reach. They never reach a true .75:1 ratio, also the track and engine combinations the owners and after-marketers add, won’t allow the motor to pull the tall gearing (pulls the rpm down on a long climb or high speed).

Common Pit-Falls: Clutches MUST be clean. Bushings MUST be serviceable. Springs MUST be replaced annually. Belt MUST be cleaned before break-in and every other ride (preferably) and within minimum width tolerance. If all of the following are complied with, see below. 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.

Note: Remember, what works for boon docking will not work for drag racing and vise versa.

Under target rpm.

Too heavy primary (drive) weights.
Too steep secondary (driven) helix angle.
Too low tension in secondary (driven) clutch.
Too tall gearing.
Over target rpm.

Too light of primary (drive) weights.
Too high tension in secondary (driven) clutch.
Too shallow secondary (driven) helix angle.
Too low gearing.

[arcticcatmatt]

Cutlers book gives a more basic lesson on theory. Once someone tells me they "get it" I tell them to read AAens book. Then its test, test, test, test.
Matt

[creepincat]

Thanks guys...I will get it yet. Sometimes it takes me a while but the more I work with something the better i understand it.