Review Submitted by Hammer…
I recently had the opportunity to put a JBS Performance clutch sheaves through its paces out on the trail. After reading some of James’ other customers rave about this kit, I was excited to get it installed on my 660 Grizzly. I was a little nervous that this kit would turn my Grizzly into a fire breathing monster and make it unmanageable in the tight trails. Not the case, though. It did, however, allow my machine make useable power throughout the RPM range.
So, let’s start with what shows up in the box. The kit comes with a new Yamaha primary sliding sheave that has been machined by James at JBS, Dr. Pulley overdrive roller weights, a new secondary spring and a couple antifriction washers to mount under the secondary spring.
Installation of the kit is pretty straight forward. If you have performed maintenance on your sheave, you can install the new sheave and rollers. The new sheave is a direct replacement and a genuine Yamaha part, so fitment is not an issue. Installation of the secondary spring is also pretty basic.
Install Video From WVHotRod Rhino’s YouTube Channel
My machine is an ’07 Yamaha Grizzly 660 with 25 inch tires. I had already done some tinkering with my clutch in the form of FIX Rhino roller weights, an EPI orange secondary spring and a 1mm shim.
Prior to installation I did some quick acceleration tests so I would have something to compare with the JBS kit. From telephone pole to telephone pole I could pull 44 MPH and in an 1/8th mile I topped out at 57 MPH. After installation of the JBS kit, acceleration from pole-to-pole jumped to 47 MPH and 63 MPH in the 1/8th mile. At first I was a little disappointed. I was sort of expecting my Grizzly to launch with the front wheels in the air and me hanging off the back. I gained a few MPH, but the “butt-dyno” wasn’t real impressed.
When I got to the trail however, I found that my initial impressions were wrong. The ATV feels like it holds every “gear” longer. It makes power all the way up through the RPM range. When climbing hills my Grizzly would feel like it needed more throttle to hold RPM and maintain speed. Not with the JBS sheave. At steady throttle it will pull hills all day long without lugging the engine. While climbing hills on the tight trails we have in Pennsylvania, I am able to maintain speed, while still maintaining control. And I still have plenty of power to spare!
Climbing a steep hill at SSRT
When the trail gets rocky, the JBS sheave shines there too. Since the low “gear” is held longer, you are able to navigate the rough stuff without having to go to low range. You are still able to maintain control as you pick your line through the rocks knowing your machine will respond when you need it.
I like the fact that I gained usable torque where I needed it and was able to not only maintain, but gain a little on the top end. If you use your ATV for trail riding, and would like a little more confidence when the going gets rough, this kit is for you. You can contact James via pm or by calling (304) 673-2602.