Mower won't disengage. The mower blade drive belt will not go to complete stop. It appears that pulley is stuck, could it be that belt is stretched or does pulley need to be oiled or greased. I have to get under mower & smack pulley to get it to disengage.

If the belt were stretched it would be harder to engage the belt instead of harder to disengage the belt. As for lubrication, this isn't usually necessary but you can certainly spray a lubricant on the linkage to help. Make sure that you do not get any lubricant on the belt or the parts of the pullies that touch the belt. If you do it will make the belts slip.

My worry is that you have an arm, a bushing or some moving part in your linkage that is wearing out. By lubricating it you are just buying a little more time. It will still end up breaking and leaving you stranded. I would try to get in there and see exactly what the linkage is getting caught on. Then order the part, lubricate it until the replacement part comes in to replace it.

Want to know how to tighten the blade belt

If it is the type that is controlled by a rod, there is an adjustment on the small rod that goes to the deck almost directly below the handle that engages the blades. It is about even with the bottom of the frame of the mower. You will need to remove a small clip and rotate the end a few turns.

If it is cable operated then there is no adjustment. It has a spring to take up the free play. You need to replacement the belt.