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2010 M8 cluthing question...slow shift from 7900-8150

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hatchers

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Nov 26, 2007
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- shift assist
- 43/36
-stock sec spring
- stock huge plastic washers on top of sec spring
- 120/340 pri spring
- shaved the weights from 68 grams down to 64 grams....99% of the weight was removed from the inside near the movable holding bolt axis (if you will)

issue: sled gets to 7900 pretty quick.....then it creeps and almost takes 3 secs to reach 8150RPM

- i cant imagine the helix is doing this as its just a one step angle change
- is this from removing weight from the inside of the weight ramp vs the outside where too much tip weight is holding me back?.....if i need to remove weight from the dang tips, how will this effort where the weight/ramps rest inside the clutch when the primary is fully open?.....maybe i should drill hole/holes in the side as to not change this?


closing argument - no im not buying a clutch kit from someone or some magic ramps....baby needs diapers:face-icon-small-hap

next ride i will - mark the inside sheeves and check after 7900 and full 81050 pulls to see what is not shifting out:face-icon-small-coo
 
Last edited:

clutch

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You have too much initial helix angle. Try a 38-36 or so. Taking weight off where you did should actually help your problem, but it all goes back to too much angle. Large spreads on helix angle work good on a drag setup where you leave the line with a relatively cool pipe and you need to build r's as you go down the track and the pipe is getting hotter, but not so good for mountain use or even average driveability.
 
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newtrout

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Why are you running a primary spring with such a soft finish? Seems like the majority of your problem right there. Did you mean to say 120/340?
 

WyoBoy1000

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does it feel like a clutch issue or is it the torque that gets you there and then the hp creeps up. which clutch is hotter. Is it a progressive helix or is it two separate angles
 

Frostbite

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Yes, I bet you have a "P" after the numbers on you helix (if it's a BDX). I have one just like it in my shop. The problem is you aren't hitting the 36 degree portion of your helix. You are probably in the 38 degree area of the helix and can't pull the weight.

You may be able to pull the weight if you drill out your tip rivets or you could add a 42/36 degree multiangle helix. With one of those you are only at 42 degrees for a short duration and then 36 degrees the duration of the shift.

I also LOVE my new Fett Brother Green/white 188/288 secondary spring. It wakes up the sled like you can't believe. I also have a Straightline 198/315 but the inside diameter is too small to fit over the center hub of the helix :face-icon-small-sad. That can be remedied but, I don't have time right now.
 

skidooboy

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truely for me, your scenario is what i shoot for in my clutch tuning. if you flash immediately to the peak rpms, you have blown through the peak torque curve of the motor and through the shift from low to high gear range in the cvt clutch.

but if you flash to a shift point, then creep up to peak rpms, you have met the torque curve and had it pull you to peak through the shift. as long as you have a good backshift (usually not a problem with the roller secondary cat runs), you will have a decent on and off switch with the throttle and, the set up will work well.

a 2-3 second delay to perfect peak rpms, isnt a bad thing to me... it is a good thing. but everyone has their own idea of what they like for perfect clutching.

ski
 
H

hatchers

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does it feel like a clutch issue or is it the torque that gets you there and then the hp creeps up. which clutch is hotter. Is it a progressive helix or is it two separate angles

hummmm, maybe it does feel like the tq does max out and then hp creeps up...but that would be hard to say

its a 43/36.....not sure when it turns into a 36, but id guess im on the 36 90% of the time while i ride and from stop to full pull the 43 is only active for a split secondish
 
H

hatchers

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Nov 26, 2007
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truely for me, your scenario is what i shoot for in my clutch tuning. if you flash immediately to the peak rpms, you have blown through the peak torque curve of the motor and through the shift from low to high gear range in the cvt clutch.

but if you flash to a shift point, then creep up to peak rpms, you have met the torque curve and had it pull you to peak through the shift. as long as you have a good backshift (usually not a problem with the roller secondary cat runs), you will have a decent on and off switch with the throttle and, the set up will work well.

a 2-3 second delay to perfect peak rpms, isnt a bad thing to me... it is a good thing. but everyone has their own idea of what they like for perfect clutching.

ski

good post:face-icon-small-coo

i got a 2010 M8 dyno that says optimal RPM is 7900-8100.....and i had 7950 for a few rides but got greedy as cat and others here think the optimal RPM is actually 8100-8300, and this 81-83 is from cat.....so?????
 
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Bacon

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Have you tried throwing the stock 36 back in and see what it does. I have never had good luck with multiangles at higher elevations. Can never seem to get the backshift I want. I thought the stock clutching is pretty good. Enough to thump some XP's.:face-icon-small-hap
 

WyoBoy1000

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If it is a radius cut helix its no different than stock after it breaks into the 36*. One easy way to get feedback is throw in a spring with 5-10lbs higher finish rate, then you wont have to grind weights and it will tell you what is going on.
 

skidooboy

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hatch, i too was like yourself, and hated to change the helix on the new reverse clutches. comming from doo and yamaha, i was scared to death of them (the unknown).

with a home made clutch tool with a base, and threadded rod to act like a press with two huge aluminum plates that are the diameter of the helix and clutch hub diameters... i have found peace with the secondary changes. i also switched out to better helix retainer bolts to make my life soooooooooooooo much easier.

now, it only takes a few minutes to switch a helix. practice a few times, it gets easier and better each time. it is a short learning curve. if you dont want to deal with it, send it here to michigan, i'll swap the helix's out for you and ship them back. i got yer back brother. LOL! ski
 
D
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If it is a radius cut helix its no different than stock after it breaks into the 36*. One easy way to get feedback is throw in a spring with 5-10lbs higher finish rate, then you wont have to grind weights and it will tell you what is going on.


This is what I am thinking too.

Don.
 
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hatchers

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If it is a radius cut helix its no different than stock after it breaks into the 36*. One easy way to get feedback is throw in a spring with 5-10lbs higher finish rate, then you wont have to grind weights and it will tell you what is going on.

thats what i was thinking......and ive changed a few helixs on these newer cats, got a pile of helix angles, broken bolts, new bolts, used bolts, broken star bits, blood stained bandages:face-icon-small-hap......yada yada
 

WyoBoy1000

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I carry three springs with me, a lot easier than changing weights, stock Y/W, SW G/W=5lbs higher start and 10lbs heavier finish, and a SLP B/P,10lbs heavier start and 20lbs heavier finish than the Stock AC Y/W. Not always perfect but get the sled where it needs to be for the day.
 
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