jabber800
New member
Need to increase engagement on a drag set up I have on a 700SX... Considering machining the spyder.. How much engagement rpm can I possibly gain by doing this, and how much effect will it have on my shift out???
Its how you can get the engagement speed up in the 6000-7000 rpm range and not run a spring that will ruin the shift curve, this allows you to use a softer spring but still have a high engagemnt speed. You just use a lathe and machine the backside of the spider. Start small at about .075" and work your way up to .100" off the back. This is basicly the same thing as shimming the old comet spiders. You are changing the belt side clearnace and this makes the clutch"smack" the belt on take off. It will raise the entire shift curve slightly, because the roller will contact the weight in a differnt spot and change the leverage, you will use more of the weights surface/curvature.
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M-Max
New member
Mr. Viper
Your knowlege of this stuff continues to amaze me.
Your knowlege of this stuff continues to amaze me.
i have done this as well and was told to cut too much out, it ended up being a good thing as i used king pin shims glued to the spider to get back some that was taken off and was able to get it right were i wanted to.
any truck gararge would have a bunch sitting around.
im going to go out on a limb and correct part of what don said. the shift curve is not effected by doing this mod. all this mod does when done alone is to close the gap at engagement between the roller and weight. this gives the weight less leverage on the roller to get the clutch to initialy move.
if you do this mod and shim your back sheave to have the same belt clearence as before it will change the curve and the engagement
this is similar but not exactly the same effect of using larger rollers.
if i screwed this up, im sorry.
any truck gararge would have a bunch sitting around.
im going to go out on a limb and correct part of what don said. the shift curve is not effected by doing this mod. all this mod does when done alone is to close the gap at engagement between the roller and weight. this gives the weight less leverage on the roller to get the clutch to initialy move.
if you do this mod and shim your back sheave to have the same belt clearence as before it will change the curve and the engagement
this is similar but not exactly the same effect of using larger rollers.
if i screwed this up, im sorry.
jabber800
New member
THX guys... I'll be separating the clutch tonight and making the cut. I really liked our last set up but could not get engagement up high enough.. Hoping this works!!!!
Scott actually it does change the shift curve as the roller no longer sits in the same place on the ramp, (the more you take off the back the higher the roller starts on the weight)by moving the roller on the ramp from the moving of the spider via machining the backside affects the balance of the starting point between the 2 axis, the roller and the pin pivot. the contact angle between the roller and the ramp determines the amount of centrifiugal force that will be converted into shift force.
rule of thumb is: about every .060" removed off backside will be 100rpm youll add to the shift curve.
rule of thumb is: about every .060" removed off backside will be 100rpm youll add to the shift curve.
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I should add also when you change the contact angle you can drop shift rpm also, it all depends on your clearance and where the roller sits on the weight. closer the angle the lower your shift rpm, the bigger the angle the higher your rpm. Small angles require more rpm to produce the same force, the larger angles require less rpm to produce the same force, this force is trnasferred into shift force which most definitely effects shift rpm.
jabber800
New member
So Don if 60th will generally create a change in shift curve of around 100 rpm, what will that same 60th generally give you for added engagement rpm? I know the weight and roller will effect this also but I'd just like to get a general idea to limit the amount of cuts I may have to make. I'm looking for an additional 1600 to 1700 rpm....
your engagement rpm is totally differnt then the shift curve, the engagement rpm will go way,way up. The engagement rises so much because the weight is more tucked in with the roller being higher up on the weight, thus the 2 axis of the weight pin and roller pin have changed geometry and it will require alot more rpm to swing the weight out, which is what you want in this case.
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if you dont move the stationary sheave then you have not changed anything about the shift curve or the relationship between the pivot pin and the roller above engagement because the sheaves still engage the belt at the same point on the weight.
you have moved the moveable sheave when you remove material from the backside of the spider, this lets the moveable sheave move outward which changes the location of the rollers,pin weight pivot point, and most definitely changes where the roller sits on the weight, youll use MORE of the ramp surface after.
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mrviper700 said:
don, again, only if you move the stationary sheave the same distance and keep the same belt clearence. by only machining the spyder, you are moving the movable sheave away from the belt. this does change the angle of the weight to the roller but only till the sheave contacts the belt. since you have not changed the distance between the spider and the sheave when it contacts the belt, you can not change the shift curve.
what you can change is the distance before engagement, this changes the angle giveing the weight less leverage, raising engagement rpm.
to change the shift curve of a clutch with out changing weight, spring, or belt width, you can only change the size of roller or neutral. these three things all change the angle of the weight in relation to the roller with everything else being the same.
my last post: when you change the point in which the roller contacts the weight you change the force applied to the roller via the 2 axis as described before, a change of simply 10 degrees equates to change in leverage which is converted into shift force!!! By machining the back of the spider you move the moveable sheave outward and the roller now is closer to the pin pivot of the weight thus reducing the amount of force and requiring more rpm to swing the weight out, this in turn starts the roller higher on the weight allowing more(longer) ramp profile to be followed and this does change the shift curve as well because you have altered the force applied to the weight, thus its not the same force appled in the same place before, your gaining more ramp in which to shift from. The curve is a steady incline and changes as it goes, so the amount of force if you start in a differnt spot would simply chnage the amount of force applied thru the roller(this force is converted to shift force) You have now also engaged the belt at a higher gear ratio, the sheave closing speed is picked up and this jerks the belt into a higher ratio instantly, its not the same spot as before, every bit you remove from the back changes this, the nuetral is wider, slamming the belt and this jerks it up in the sheaves. If you dont think so, simply mark your belt contact area and the sheave face with a black marker. Then install a machined spider and see where the belt is then grabbed, youll find out it started out in a higher ratio then before from the force appled to engage the belt, this changes the gear ratio and the place in where your roller was on the weight before machining of the clutch.
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tippmannator
New member
holy crap! my brain hurts from reading all that!!
jabber, if you are useing the high engagement snap for asphalt?? that might not work!! ben there done that!! want to have a high but smooth engagement for good 60ft times. my 2 cents.jabber800 said:
We will have to agree to disagree. I agree with you, then we would both be wrong. That wouldn't accomplish anything now would it.
jabber800
New member
Magic this set up is for a sled running on the grass... I would have to agree with you that this would probably not work on the tar. Really looking to improve the 60 ft. time on a sled that is pulling hard mid track on grass.
not to step on any toes here, but Yamaha actually listed this cheater mod in their 94-96 V-max twin grass drag manual. i did this on several clutches and it worked well. however, this was a race only mod that would fail terribly on a trail application. the specs are in the manual printed by Yamaha. i have it at the shop if anyone interested.