488 roller sprocket burning up

I'm new to this and I have a 488 that has been in the barn for the last 15 years. I decided to take it out and try to cut some grass hay this year.

Before I took it out, I greased everything, checked gearbox, oiled the chains and ran on the tractor. I noticed there was a lot of slack in the chains, like 2 inches of slack in the lower roller chain and it was banging around. I tightened it up to about a 1/4 inch as per the manual.

Then I ran it in the shop at half speed for about 5 minutes and noticed smoke coming out of the left side and sure enough the lower roller chain was smoking hot, and had burned off all the oil. After it cooled I noticed one idler sprocket was very stiff and the other was very very sloppy feeling.

I took the chain off and replaced both idler sprockets with new ones and put the chain back on. When tightening the chain, it would only seem to get tight on the bottom side of the lower gear while the top stayed fairly loose..

I took it out and mowed a couple acres when I saw smoke from the left side again, one of the new idler sprockets has burned up again already.

Any ideas what is going on here? Why would the chain only feel like it's tightening on one side?

488 roller sprocket burning up