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Hello all,
I have been enjoying this forum for over a year now having gained much knowledge from the the local gurus. I recently purchased a Coop #3 sheave and finally got around to plugging it in, I have to trailer the Grizzly to ride it and just want to see if my findings are correct first. I do understand there could be manufacturing differences on many components to effect results. So I had a stock starting ratio or 2.5:1, after installing the new sheave (no shims) it came in at 2.75:1. Picked up 6 primary fin spaces from 2 12/24 to 2 18/24ths. Does this sound consistent with the ratios others have got with sheave only install? I have read or many different ratios and was thinking it would be a bit closer to 2.9. I have rotated it, torqued to 103'# and ran it briefly in nuetral with no rubs that I am aware of. Thanks for any insight offered.
 

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I have coops machined sheave and what you gain is about 25% more lower gear without losing any top end, adding a .5mm or.7mm shim will get you close to 3:1 without rubbing and little top end loss, not all machined sheaves give the same results it seems, some experience more ratio, others not so much, clutch weights 18-20 gram are the norm with most using the EPI Purple spring in the secondary.
 
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What he said.....

-Stock vs Coop45 machined sheave

-2.45:1 stock

-Coop sheave +0.5 shim 3:1 - 3.1:1 ratio
 

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OK then it seems 2.75:1 would be typical with milled sheave only. I was hoping that the milled sheave would take care of a little more ratio than that... Being I did not want to add shims and reduce top end speed. What does not make sense to me is if milled sheaves are "said" to be good for 2.5mm to 3mm worth of effective shim... then why did I only achieve a small gain from 2.5:1 to 2.75:1 with effectively 2.5mm worth of shim. But adding another .5mm of actual shim would take me from 2.75:1 to 3:1+/-? I guess that is what I am wondering. I guess I believe it is installed correctly so I will run it a few times and see if I want or need to go there with an additional .5mm shim.

Vincent, that third picture of yours seems really aggressive. Do you have excessive rub with that setup? what does that one give you for mph top end loss?

Griz7, I believe I am happy with the 18 gram stock weights at this time, we do some cruising so I would not want higher full time rpms.
 

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Your results are pretty much spot on. I have the Coop #3 also and I’m at 2.9:1 with a .5mm shim.
 

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OK then it seems 2.75:1 would be typical with milled sheave only. I was hoping that the milled sheave would take care of a little more ratio than that... Being I did not want to add shims and reduce top end speed. What does not make sense to me is if milled sheaves are "said" to be good for 2.5mm to 3mm worth of effective shim... then why did I only achieve a small gain from 2.5:1 to 2.75:1 with effectively 2.5mm worth of shim. But adding another .5mm of actual shim would take me from 2.75:1 to 3:1+/-? I guess that is what I am wondering. I guess I believe it is installed correctly so I will run it a few times and see if I want or need to go there with an additional .5mm shim.

Vincent, that third picture of yours seems really aggressive. Do you have excessive rub with that setup? what does that one give you for mph top end loss?

Griz7, I believe I am happy with the 18 gram stock weights at this time, we do some cruising so I would not want higher full time rpms.
I believe Arnie Cooper told me his #3 sheave is about the equivalent of 1.5mm shim with no top speed lose. Which makes sense since I was at 2.75:1 with 1.5mm shim before I got the coop #3
 

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Discussion Starter #7
Your results are pretty much spot on. I have the Coop #3 also and I’m at 2.9:1 with a .5mm shim.
That is really good to hear. so with your .5mm shim what was you top end loss?
 

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I guess I should order a couple .5mm shims. I have a 1.2mm from someone but I am sure that would be a bit much.
 

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I just installed the coop last week and have only been able to ride it on my property so far, have put about 20 miles on it but I have not been able to test top speed. I can tell you I now top speed loose in low gear
 

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I guess I should order a couple .5mm shims. I have a 1.2mm from someone but I am sure that would be a bit much.
Order a .5mm and a .2mm or a .7mm so you can try .5mm and .7mm they are cheap enough and then you can experiment
 

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FYI- I did try 1mm with the coop and ended up with 3.1:1 but then the belt rubbed so I went back to the .5mm, some of the guys here are fine with the belt rub on the cover.
 

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Sounds like a good plan a .5 and .2 they make them that thin? huh. What did you mean here?
" I can tell you I now top speed loose in low gear"
 

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Sounds like a good plan a .5 and .2 they make them that thin? huh. What did you mean here?
" I can tell you I now top speed loose in low gear"
I think I have seen a .2mm shim. If not I know .7mm is available.
what I meant by no top speed lose in low is I could max out at 30mph in low gear before the coop 3 and I can still hit 30mph with the coop3 but I get there a lot quicker
 

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Discussion Starter #14
Well that is encouraging then. I will order up a set of shims then. I dont think I have ever been over 12 mph in low, period.

And my understanding is I will not be encouraging any long term engine damage I with these clutch adjustments, correct? I guess I have never read anything, and plenty of guys here doing it.
 

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Correct. No long term damage. Many guys have thousands of miles on these set ups. Vincent & Ridgeway can attest to that
 
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That is really good to hear. so with your .5mm shim what was you top end loss?
With a 5mm shim your only talking 2-3 mph loss on top if that at most, some can get away with 7mm shim without belt rub and puts you at the 3:1,with around the same top end loss, your ratio will increase as your belt wears in, I never trail ride right to the pin all the time so top end is not important to me, I installed the machined sheave mostly for towing a loaded trailer, I have the factory 18gram weights also, 20 gram would give me better mileage I would think for trail riding.
 
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Discussion Starter #17
Thank you guys for helping me sort that out, appreciated! :cool:
 

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Thank you guys for helping me sort that out, appreciated! :cool:
Later to the party, don't know why I just saw this thread so...
Starting with the first post about 2.75, did you buy a sheave from COOP and keep your stock sheave? I would call Arnie and ask a couple questions if so.
These mods don't hurt the engine other than more fun, thus more riding :)
The damage can be from not installing something right and starting the engine.
The reason shim with machining works well is the shim magnifies the machining benefit, makes better better.....like multiplying 2 x 2 = 4...then multiplying 3 x 2 = 6, you're starting with higher a higher ratio which then changed more shim...the ratios expose this by seeing what .5 does to a stock ratio versus a machined ratio.....bigger gets bigger faster and.......the last mods are harder to get right and have room for.
 
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