HOT ROD SLED SHOP SKI-DOO REV GEN4 engine mount shim kit includes a 4 pack of .020" motor mount shims that allow more compression of the mount or stacking of the mount, allowing less engine movement under load for more precise clutch alignment. This also allows the center to center to stay slightly longer and more importantly not shorten as the motor pulls back and up under torque. A combination of these shims under the left rear motor mount with the Poly bushing and sleeve shortened slightly combines with our QRS shim kit allows proper alignment and is easily checked and verified with our alignment bar. The new 2019 Ski-doo alignment specs are much more precise and closer to what we found to be ideal for the Gen4 850's ideal settings in our field testing. The new2019 specs are printed on our newest alignment bar. Our alignment procedure is included in our QRS shim kits as well. Check out our alignment bar, polyurethane motor mount, and new QRS shim kit!