Is bar clean out under chain, chain on backwards

not familiar with 61, My guess is your not lining up the chain adjustment tab in the chain cover and it's pinching when you tighten up them cover nuts. Or if it has chain brake the brake strap is warped and braking the clutch drum?

I think rc has something there. I recently had my chain brake loop get out of shape on me and the chain would lock up either immediately or after a short running period. And yes, I could imagine someone failing to get the hole in the bar to mesh with the tension adjuster.

The bar is spotless. Not a speck of dirt. I cleaned it, reinstalled everything and the symptoms are the same. I removed the chain brake band/loop quite a few years ago. The tensioner is installed to the bar properly and is increasing/decreasing the bar/chain tension as it should. No problems there. I'm suspecting the bar or sprocket, possibly the chain but I haven't played with one of these in years. The Husky 81 is a 61.5 CC from 1989.

probably need to look at the sprocket that's welded to the clutch drum. if it got deep teeth wear it probably locking up the chain. I've only had to replace 1 sprocket on my saws. just wanted to make sure you done all the easy stuff before you started changing stuff. My next guess would be warped bar if the sprocket is pristine??? or maybe bad or missing needle bearings on the clutch drum???