Yamaha Grizzly and Kodiak CVT

This post I am writing up in response to a question Pat McSharry wrote on a Facebook page.

The Ultramatic CVT is identical between the Kodiak and Grizzly other than the primary sheave weights are different, Grizzly usually has 16gram or 18gram weights where I believe the Kodiak came with 28gram weights.

So I will split this into three sections.

Primary Sheave and Shims:
This affects the drive ratio.
Shims give you “lower gearing” so to speak, if you put in 1.0-1.5mm of shims it will push the primary sheave apart allowing the belt to ride further down giving you a steeper ratio. This mod is cheap, maybe $5.00 in parts as long as you have the tools, the only downside is you will probably lose about 5mph on the top end. Going above 1.5mm requires caution as you can damage several parts of your CVT.
If you want to go even lower or still maintain top end we can discuss having the primary sheave machined, I run a Coop45 machined sheave on the Grizzly for about 6 months now. I am not sure if the machining cost is worth it as I rarely run WOT at top speed anyways.
Modifications to the primary sheave and shims are the only way to change the bottom ratio.

Roller Weights and Cam Plates:
I will put it right up front, overdrive weights are not worth messing with on these machines, converting to greaseless weights may be worth it if you swamp your atv in deep water frequently. Also do yourself a favor and leave the stock cam plate alone, some guys will try to mod that and I feel that it may make your CVT less reliable.
But the roller weights are easy to replace as well and they affect how quickly “shifts” so to speak.
Grizzly comes with 16g and Kodiak comes with 28g, there are 8 weights in the primary movable sheave that ride against a cam plate. As the RPM’s go up the weights push outward against the cam plate and that in turn pushes the primary sheaves together which forces the belt outward into a higher “gear”.

Secondary Sheave and MainSprings:
Not alot to change here, just the spring ratio and possibly add in teflon polymer washers.
The spring rate here also affects how quickly it shifts so to speak, and also can provide more pressure on the belt to help with slippage if you run really big tires. The teflon washers can help the sheave to not bind on the spring if running heavier springs.

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How I go about tuning a CVT.
First: I start with the shim mod, this lets me feel out the starting ratio, usually losing 5mph on the top is not an issue so I would do 1.0-1.5mm right away. 0.5mm usually isn’t enough to screw with it. If the person is really concerned about losing that top end we can discuss machining but that usually runs $200-$300.

Second: If running oversize tires I recommend installing a heavier secondary spring automatically, but if sticking to 26″ tires or less swapping this spring may be unnecessary. This will hold the CVT in a lower ratio longer, on the positive side is that you feel way snappier response when accelerating from 5-30 mph The downside is that because you are turning more RPMs at a given speed it will hurt the fuel mileage a bit and you may find that the exhaust tone gets a little annoying when cruising at slower speeds.

Third: Adjust the Primary weights to fine tune the midrange of your CVT, every 2g change in weights will affect your engine speed by about 200 RPMs at 25MPH

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On the Grizzly I run a machined sheave with 0.5mm shim, Purple EPI secondary spring, and then actually went 4grams heavier (20g) to drop my cruising RPM’s a little bit as alot of riding I do is between 25-35 MPH. This setup is perfect for heavier tires that are 27-29″
The Kodiak is stock at the moment, but will be putting in a 1.0mm shim and also replace the 28g weights with probably 20g weights as well this spring. Its too cold to mess with it right now.

My recommendation for your Kodiak if you are sticking with stock sized tires would be to put in 1.5mm of shim and then switch to 20g or 22g weights. Also we can talk about how much weight you might be carrying or pulling and what kind of riding you plan to do with the ATV.

Hopefully this helps.

Here is a pic of the Grizzly, The tires are about 27.5″ in diameter.

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Wow small world that you saw me asking about it on the grizzly Facebook group. I really enjoy tinkering with this kind of stuff, but the last thing I would want to do is make the machine less reliable than it is stock.

I honestly don’t really trail ride that much, I really just use the machine for ice fishing and plowing snow. I just noticed that the grizzly’s do feel a lot snappier than my kodiak.

I typically pull an otter lodge if I pull anything. Once I install an otter monster box on the back I won’t be pulling a fish house nearly as often.

Thank you for the detailed write up. Do you actually sell clutch kits?

I should say, I purchased a 2018 Kodiak base model so it doesn’t have a locking differential. Adding that would probably be the best mod I could do to it at this point.

Yeah I saw your post over there and recognized the name as I watch IDO all the time, on a side note I really appreciate the time you guys spend analyzing lake maps it has helped me immensely to know what I am looking for.

I dont sell any ATV parts, just know how to work on them and am pretty active in helping my fellow Yamaha riders out. My Grizzly is more trail tuned and the Kodiak is more of a workhorse.

As far as your needs go (pushing snow, pulling sleds) I would look at 3 things:
CVT mods, tires and possibly adding a locker to the front.

CVT I would keep it simple and just do a 1.0mm shim and drop down to 20 gram weights. This will not affect your reliability at all as long as the primary is reinstalled correctly. Normally takes me about 2 hours but I would budget 4 hours, or if you are like me somehow you will be missing a couple tools and have to run to the local Fleet Farm or Home Depot… Cost is $3 for the shim, $28 for the tub of Ultramatic Grease, $80-120 for the weight set. It will give you about the equivalent of a 10% underdrive ratio.

Below is a good video on the process (other than using an impact wrench to tighten the primary nut, This needs to be torqued precisely to 100 ft lbs)

If done correctly your dealer wouldn’t even know you modded it unless they tore into the CVT for some reason.

Tire choices can get crazy, the stock tires are marginal in my opinion, plus with the clutch changes you can easily step up to true 26″ tires that will give you about an extra inch of ground clearance.

Then there is the front differential, front diff lock is handy to have but its also a good way to break a front axle. Put in low range with diff lock engaged and both wheels spinning is fun but if only one side grabs wrong the other side is still spinning and the torque has to unload somewhere… Factory diff lock reduces the power to prevent this from happening.
honestly I have only needed diff lock a couple of times (crawling over downed trees in the rain and also crawling up a slick rock incline)