There is a band clamp like is used on the fuel injection intake rubbers that uses a screw and nut instead of that worm gear to tighten. If you can get one of those in stainless you might be able to hook the spring directly to the screw shaft, either as a hook or peel out a full loop and thread the screw through it. That gets you the same as the washer idea except for bending the washer. Nobody in the history of washers ever accurately bent one on purpose. They got that written down somewhere. Now accidently bending a washer, especially when it's a bad idea to have one so, is a fairly commonplace event. It's important to understand the difference if you're going to get into the nuances of washer bending. Just sayin.
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This clamp idea was something we did on the loops when the big nut threads got messed up past dealing with. It worked until a combination of the vibration and the spring walked the clamp down the pipe, making the spring ineffective. The heat/cool cycle didn't help either. I mentioned a comment in another topic where Gordon describes his fix for a very similar situation using a wrap of rubber to stop the clamp from walking. The topic he commented in was about hanging a pipe not anchoring a spring, but the problem is the same. Since you aren't right up against the head with the rubber, it might work for you, too.