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your clutches and you

Snowmobile How-To's

 
 
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  #1  
Old 10-20-2007
Madcow's Avatar
Madcow
1050 one lunger
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Join Date: Sep 2007
Location: pine city mn.
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Default your clutches and you

well this will be a simple overview of the basics of your clutches. later this winter I want to make a clutch movie to show how to inspect and repair the clutches and then how to do some clutching.

first off you have a primary clutch bolted onto the engine. it has a stationary sheave closest to the engine or back of clutch. then you have the movable sheave. inside the moveable sheave are the weights and spider. between the spider and cover sits the primary spring. as the motor spins faster the weights push against the rollers in the spider. making the movable sheave want to move in for upshift or to make the primary clutch bigger in diameter. the primary spring is trying to bring the clutch back to open or down shift or low gear. its a pretty simple operation for the most part. if the wieghts have more force than the spring it shifts up. for all brands primary springs are pretty much the same, they have a primary rate in lbs, that is used to dial in engagement rpms. a high spring rate witch is used for shift rpms or help dial in wide open throttle rpms. and they have a shift rate. and that is the amount of force to cover the distance of clutch travel. if you take any one or all the numbers up the rpms go up. for polaris and artic cat weights are pretty easy because they are listed as trail aggressive weights or racing/mod style weights. for all the newer wide roller polaris and cat primarys you can pretty much jump around in wieghts and not have to worry about reshiming or getting into radical profiles of the weights. yamaha uses riveted weights. so if you want to dial in low/mid/or top end you can do it. or you can go to a bigger base wieght and put all the same rivets in it. very tuneable but you need a little understanding of how the mass location on a weight can affect clutching or you can have huge overrev or bog out of the hole and spot on mid range and huge overrev or bog on top end or any combination of overrev/bog throughout the rpm range. the ski doo tra is about the most adjustable primary out there. but it is more complicated to work on and takes a lot more to understand. the pins that hold the ramps(weights) are on an eccentric. so you can change the ramp to roller profile by rotating the pin. wich in turn makes the weight more or less aggressive. kind of like changeing the amount of weight in the other clutches, then you can also get different angle ramps and different weighted ramps. but in the long run it works the same.

the secondary on all 4 brands and everyaftermarket clutch are the same. you have an inner movable sheave, a helix, spring and stationary spring. the helix wants to upshift the clutch and the spring wants to down shift the clutch. on every clutch to make them upshift the movable sheave has to turn against the pull of the belt. so if the sled is in the garage and you want to push the clutch open you have to spin the movable sheave backwards and push to make it open. thats how torque sensing works. with little resistance on the jackshaft(the shaft the clutch is mounted on) the stationary sheave will turn that tiny bit faster than the movable sheave because the belt is being pulled into the clutch by the primary clutch getting bigger in diameter. as you start to increase load by going up hill and you hold the throttle in the same spot so the rpms will stay the same. the load on the secondary starts to build slowing down the upshift. at some point the load becomes to great to maintain speed and as the belt pulls harder the movable sheave gets pulled against the ramp and with the help of the spring starts to back shift.
for the most part you can toss any helix with any spring and make it work. it wont be great but it would function, the clutch will open and close if you have a miss match, either to much spring pressure and not enough helix angle you can get a lock up condition in the secondary, where the helix angle cant overcome the secondary spring so the secondary is locked up before you get full shift out. the primary is going to try and keep shifting out. if you are lucky your rpms will be low and make you take notice. if you dont pay attention you will overheat and blow the belt. if the helix is to big for the spring pressure you get slippage off the line or bogging in loose snow or coming out of corners.

when building a clutch kit you have to start with rules of thumb or theory.
lighter wieghts rev quicker and usually get a faster et or better for drag/ditch banging
bigger helix's with stiffer springs give a faster upshift
smaller helix's give better traction off the line and backshift faster
softer springs get into overdrive easier
bigger weights give a smoother acceleration and usually build more mph

but now if you have a team clutch it goes against all these theorys and thats why you can now buy torsion spring kits for team clutches, so you can go to lighter springs. and that is also why that usually a team will scrub off mph and make you have to pull heavier wieghts in the primary to help it shift.

to build a clutch kit you have to know what you have now in your sled. and then you have to look at what you want to gain. for every old indy that has a red spring and straight 34 or 36 degree helix chances are you want a quicker snappier feel to the sled. the older sleds were setup for smooth trail acceleration with gearing about right or a little tall. the newer sleds give you that snappy feel but as we went for the ditch banging/quick drag clutching setup with the team clutch all these people want is better top speed and a little more feel to the sled. so you have to look at the basic theorys of clutching and see what you can do. each motor is going to be a little different. the 800 twins have a very narrow hp curve. so if you are off by a couple hundred rpm you are giving up a lot of hp that you dont have to begin with. one good thing is to have your tach calibrated and use a test sled. one of your buddies that is close to your sled or a little faster. make 6 drags with each other and some rolling starts and make notes of your rpms and how the two sleds compete. then make one change at a time and then run them over the same tests and see if it improved. chances are your first 6-12 changes might get you alot or loose a lot so keep notes and pretty soon you will see a pattern and you can go from there. if you are going to make gear changes or track changes to make them first.
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  #2  
Old 10-20-2007
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Default your clutches and you

Thanks Madcow! Chalk another one up...
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  #3  
Old 10-22-2007
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Default your clutches and you

Wow, great write up Madcow
(Pics would be great for dum-dums such as myself ;)
Can't wait for your movie. I'm very intrigued by clutches and clutching.

You mentioned engagement RPM's. How do those affect sled performance, and what are your personal thoughts about what is considered too high/low/just right.
(but I assume those numbers all depend on what you want out of your sled too, correct?)

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  #4  
Old 10-22-2007
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Default your clutches and you

ohhhhh I can't wait to get the XCR home and have the mad scientistwork it over!!!!!
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  #5  
Old 10-23-2007
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Default your clutches and you

Maybe you can name the movie "clutch rebuild for the dummies" WL.
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  #6  
Old 10-26-2007
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Madcow
1050 one lunger
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Join Date: Sep 2007
Location: pine city mn.
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Default your clutches and you

^^ :laugh:

engagement rpms are actually easy to tune and hard to screw up but have some huge gains if a person is willing to play. for a trail sled the easiest thing to do is go out get it hot. then stop and punch it. is it coming on hard or when the clutches grab is there a slight hesitation in the rpms from climbing. at the current engagement rpms can you easily move the sled or do you have to kind of gas it? if the engagement is on the low side on warm days you can get bogs, or you can get some belt burn if the load is high enough. like if you stopped in deep warm snow and then try to punch it. if the rpms are a little low the sled might not have the low end hp to get it moving easily and will actually grab the belt and bite hard enough to burn it but not hard enough to move the sled.
To high of an engagement and basically you can have lots of spin out of the hole. on a trail sled you are better off with a higher engagement. since most of your trail riding is done at 1/4-3/4 throttle.

on ice for racing when you are going for speed you want the rpm to be as low as possible to start shifting as soon as possible. for drap you want the higher engagement to shift as hard as possible. for speed running on the 800 I had the engagement as low as 3500 rpm with big wieghts and it left the line just fine, with the lower engagement you can run less studs since you are leaving the line easier. less studs means less rotating wieght meaning there is a chance you can go faster. years ago some open mod guys did some testing and the only thing they changed was engagement rpms. as they kept lower the rpms they kept creeping up in speed. until the rpms got to low and when they would throttle the big motor it would bog.

another funny thing about clutching. a 700 twin at 130 hp will pull almost the exact same clutching as a 160 hp triple? why because the clutching is torque sensing and both motors spin about the same amount of torque. but the triple also spins a few hundred rpm higher. making the wieghts actually act heavier than the same wieght in the smaller motor.
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If the boner police are here I need a lawyer.

in a time of deciet telling the truth is a revolutionary act. george orwell.

aint no body ripin like me. M to the a-d-c-o-w. rock it hard for my fly ladies. I rock it yes in deed. homies still roll with me. money dont change me


nothing goes like 3 holes.

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high performance engineering
aaen performance
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