Quote Originally Posted by PapuaPilot View Post
Typically you install the final (permanent) weights on the spinner backplate as far outboard as possible. Use a screw/bolt, self locking nut and washers as needed to make the correct weight. You will need to drill a hole in the backplate at the correct clock position. Make sure it doesn't rub on your cowling. ...
That’s definitely the FAA approved/recommended way. I’ve balanced many dozens of props on experimental aircraft, but I just hate putting holes in a spinner backing plate. If something changes (new prop, etc.), the ideal location for perfect balance weight addition may be just slightly off of that hole, or at the very least you may now have an unnecessary hole in the plate and have to drill another one in a new location. With Lycomings it is often possible to do a good job utilizing the holes that are in most of the “newer” ring gears (every 30 deg.) and adding bolts, nuts & washers as necessary. Otherwise I have used automotive stick-on lead wheel weights very successfully. I carefully clean & gently rough up the inside of the back plate flange in the proper location(s) and apply the weight(s) there. I remove the foam mounting tape that comes on the weights & replace it with high temp/high strength 3M tape. I’ve also molded my own thin lead strips to use when only small amounts of weight are necessary and I want to have a greater contact surface area for adhesion. The lead is easily trimmed to the correct fractions of an ounce or gram. After the weight is applied and final balance check, I then apply a thin fillet of silicone sealant around the perimeter at the base of the weight to seal the edge of the foam mounting tape against air & moisture. In the approximately 25 years I’ve been doing that, I’ve never heard of a weight coming off. However, if you do need to rebalance with new weights, they are easily removed with no damage to the spinner backing plate. FWIW.