I removed the check chains after using a penetrating oil I borrowed from my B-I-L. This stuff works better than any penetrating oil I have ever seen. I really did not think I would get those bolts loose but I applied this stuff and let it sit for about five minutes and they turned fairly easily.
After removing the check chains and then applying same stuff to the turnbuckles, I waited again for five minutes and was able to turn both with no great difficulty. I didn't even put them in the vise.
If you had seen the threads on these things, you would understand my amazment.
Kano Kroil. Made in Nashville Tennessee. (no involvment with these people in any way.)
Gary