No you did nothing wrong, It's really the nature of the .81 Rossi, to just run itself into oblivion. The .81 Rossi's are terrible vibrators and combine that with a high revving fan unit and something is gonna give. I had many .65 rossi's in my DF's and every once in a while the crank would break. In the future make sure the rotor is well balanced, try to stay away from the .81's unless you are using a Byron fan, the .65 rossi's are just about indestructable and would probably work ok in the ramtec, though it may be a bit much for the .65. Forget the .46VRDF it's not going to spool up the ramtec. You may want to look into the classifieds for, O.S.91, 77 BVM .82, .91, 96 CMB .65, .91 K&B.82

Hope this helps