is it where the front sproket is at the pivot of the rear swingarm and if they don't have this do chains snap more/ a lot

 

Basically, what it means is that if you don't have it and you do alot of jumping, you'll need to install an aftermarket chain tensioner (AAEN and HPD make one.. Im sure there are other manufacturers..)
I've heard horror stories about people jumping Polarises and breaking chains on Non-Concentric drive models... Most of which is because they either don't take care of their machines, or the don't know how to properly adjust the chain.
My Scrambler 500 is a 97 model, so it doesn't have concentric drive.. I jump it, mud it, carry passengers and ice chests on it.. and have never broke or tossed a chain..
There is a guy in one of my classes at college bad-mouthing Polaris because his Express 300 2WD chain broke (its several years old) Granted, this guy would field dress at over 325 lbs.... I asked what happened when it broke, he said," I was jumping it, and when it landed, it just snapped... Dammed junky Polaris..".. I'm standing there thinking.. How does this 300 even pull him...???? Let alone JUMP!!!
Anyway, All new Polaris quads have concentric drive, so you shouldnt have to worry about it....

 

Click <A HREF="http://www.pddnet.com/dtopics/0997F5.HTM">here</A> to find out all you want to know about concentric drive.

In a nutshell, it is a viable alternative to shaft drive, able to deliver high torque and response.

 

where can i get a chain tightner from and how much do they cost

 

could u purchase a concentric drive system for a 96 polaris 400 scrambler and if so how much

 

I think the AAEN chain tensioner is about $50.00..... Don't quote me on that, but its somewhere in that area...

 

I don't believe so. Take a look at your rear swingarm's mounting pivots. On concentric drive the pivots are in line with the sprocket in other words imagine if you have a long rod and you can push it through the center point of both swing arm pivots you shough also pass through the center of the sprocket. On older Polari the swing arm is designed like any other bike and the chain must have play durring the swing arm travel. Concentric drive is one of the many bonuses that Polaris provides over other manufaturers. Unfortunatly a chain tensioner is you only alternative but a good one.

Chris Picciotto
99 Scrambler 500