I didn't realize that you were using 1" diameter "turning block". So, given your discription, I think you may be overloading the block. (I thought you were using a "real" turning block

The normal load on a "normal" 1" block would be in the hundreds of pounds; however, using the 180 degree (in-and-out the same direction) you have the maximum. Using the 160 degrees, you're not very far from that. (The 45 degrees is only a little bit of the load.) You remember your sines and cosines ;^).