Leny, the best solution I've tried is to use a piece of chain with just a bit of slack left in it. If you 1/4" chain and have about a 1/2- 3/4 inch of slack it'll come tight with any serious amount of torque. But the vibration is lacking when 'cruising'.
I've also used, when dealing with a motor plate, a couple of inches of fore-'n'-aft 3/4 inch tubing welded into the plate. Then you fill the tube with rubber hose, with the ID just right for a bolt. Sheet rubber at both ends of the tube protect the ends of the tube from the 'ears' on the chassis.
KS