Ok after i have just rebuilt my bike i have this very bad problem. I bought a new chain rated for 165hp so its strong enough no problems. The real problem is that now i have to much power (toruque) i keep shearing off the studs that hold on the rear sproket. I use new studs and nuts since u can only use them once. Ive put them on it shears them off, so i had a yamaha mechanic do it, and it still wont hold. Do i need to drill out the sproket and hub to something larger and but bigger class 8 nuts and bolts or what do i do now?