My thoughts on Yamaha's X2/X4 wet clutch.
Reference video:
First of all I'm going to give credit to JBS for discovering that the X2/X4's wet clutch uses rubber bushings like Kawasaki Teryx's wet clutch. I don't like stealing other's information (as my own) and am willing to give credit where credit's due. Here's where we'll disagree. You'll see in James' (JBS) Teryx wet clutch video that he tries to move the clutch shoes in and out and has difficulty doing so vs the Yamaha (Rhino\Gen1\Viking) wet clutch which doesn't use grommets. The problem is that he's doing this on a new clutch that is dry, without the benefit of oil. I'm very confident that the clutch shoe will move in and out much easier with oil present. He sees these grommets hurting wet clutch performance. I see the opposite.
What the hell are you talking about Massive?!?! Basically you have a rubber grommet installed onto a post behind each clutch shoe. Each clutch shoe has a corresponding cylindrical hole cut out to match that rubber grommet. Under centrifugal force the clutch shoe will break-free and engage the clutch drum. The Teryx wet clutch also uses weaker springs than the Yamaha's.
Massive's thoughts: This makes perfect sense and isn't a flaw in my opinion. By using the rubber grommet design, what you're essentially doing is getting a higher stall speed. This can be done by using stronger springs, but if you use stronger springs, you reduce the clamping force exerted against the clutch drum. To refresh your memory the springs are there to hold the shoe back until the clutch is spinning fast enough to engage the drum.
By using a grommet, you can actually use weaker springs = have your cake and eat it too. The grommet raises the stall speed over a non-grommet design. The weaker springs increase force against the clutch shoe and lower stall speed. They equal each other out so you have a normal stall speed, but increased shoe pressure against the clutch drum for less slippage.
The're aren't any holes in the shoes to add weights so forget adding slugs to your wet clutch unless you're going to drill those holes yourself (which I don't recommend), and how much benefit would you be gaining over the weight of the material removed from drilling that hole in the first place?
What I do see as far as modding is changing either the thickness/size and/or compound of that rubber grommet to increase/decrease your stall speed. Removing it would lower your stall speed/shoe engagement. Also consider that synthetic oil could affect the slipperiness of that grommet, allowing the shoe to slip out easier.
One con: you better do timely oil changes as I can see those grommets eventually breaking down/wearing out and you don't want that crap running through your engine.
