Originally Posted by
headloss
Fender mounts aren't just drilled into the frame, they are tapped into braze-on's that are (I believe) welded on and reenforce the hole. Drilling a hole and tapping it without reenforcing it, is just asking for trouble imho.
These are factory drilled and tapped. Unoccupied and ungreased for nearly 20 years. No rust problems. The tp two aren't even ChroMo.
I'd bet that if the OP stayed away from where the stress occurs, he'd be OK.
Proceed with caution though.
