Would really appreciate some help

Hi there, I’m new here so I apologize if I’m not following any of the proper etiquette.
I have an issue with a robot character mesh I’m working on–I’ve used Rigify to automatically rig it and for the most part it’s working rather well, but I have a problem with the chest.
Namely, it distorts when I move the arms. This wouldn’t be an issue for an organic character but, well, this isn’t an organic character.

If at all possible I’d like to be able to move the arm without having the chest stretch the way it does.
Here’s how I have the arm weight painted:

The chest is similar in that it’s red, I would attach an image but there’s a 3 image limit.
Please let me know what I’m doing wrong, I’d really appreciate it. I’d like to get this done as soon as possible. Thanks again.

Select all the chest vertices. in the mesh properties tab, in vertex groups panel click on the arm group name and press Remove. To check press A in the 3d view to deselect all and in the vertex groups with arm group selected press Select. Only arm vertices should light up. Do a similar thing for the chest bone to see what verts it is controlling. etc. For non oganic hard objects no vertex should be assigned to more than one bone. Rigify is really designed for organic deforms only (unless it’s been upgraded a lot…)

Thanks a bundle! That did the trick. Much appreciated!