Remove the drive end cover by removing the large nuts/bolts. Remove the bar and run the motor for a few moments, which should reveal oil oozing out of a side port where the bar fits. If ok, then spread out the chain so that it can be inspected for any damage that may have occurred. Check the bar itself for any damage. Clean all of the parts including the oil passages in the drive end of the bar and the entire chain groove. If there is a sprocket on the bar end, make sure it turns freely. Check the drive sprocket teeth for extreme wear or damage. If all ok, insert the bar and push it back toward the motor. Then thread the chain over the sprocket, then over the bar. Pull the bar out, replace the cover with mounting hardware finger tight and make sure the adjustment 'tang' fits into one of the large holes in the bar. The chain teeth need to cut toward you on the lower run of chain. Adjust the chain until the chain pulls up to the bar, but can be pulled by hand. Tighten the mounting hardware and recheck chain tension. Make sure the chain is properly sharpened. Hope this helps!