This is a polyurethane engine torque stop for 2017-2021 Ski-doo Rev GEN4 850 models with the " floater motor". This engine torque stop will limit the motor movement under torque (especially combined with our HRSS engine mount shim kit) and stop some of the "float" in the mounts helping to cure the motor/belt misalignment going on. This poly stopper with modified center pedestal combined with our HRSS engine mount shim kit and left rear shimmed motor mount results in a very solid and more precise clutch alignment. We offer complete instructions for the poly mount modifiction, HRSS engine shims combined with our alignment bar that gets you to our prefered alignment specs which incidentally is closer to the new 2019 Ski-doo alignment specs. Our new alignment bar is now printed with OEM ski-doo 2019 specs, XP/XS specs and we include our prefereed alignment specs for the GEN4 850 on our QRS instruction sheets as well. NOTE THAT WE MODIFY THE ALUMINUM PEDESTAL AND COMBINED WTH OUR ENGINE MOUNT SHIM KIT AND QRS SHIM KIT HAVE ACHIEVED EXTREMELY RIGID MOUNTING WITH GOOD OFFSET AND PROPER ALIGNMENT UNDER TORQUE WITHOUT BUYING A $200 ALIGNMENT TOOL PLUS PARTS!