What kind of screws can I use to fasten heat shield to underbody?

I have 2006 Ford Focus. The sheet metal on the bottom is rather large, and it fell off again. Before, I had secured it with bolts and over-sized washers. But now, the areas around where the sheet metal is supposed to be secured to the underbody have frayed so much, I cannot fasten the heat shield again by using the existing posts and nuts. I am thinking about using self-tapping machine screws to fasten the heat shield onto the underside.

My questions are:

  1. Is it O.K. to drill holes on the underside of the car? I am concerned about the new holes rusting out and eventually making holes on the floor board.
  2. What size and type of screws should I use?

Does anyone have any other ways of getting the heat shield onto the underside?

Not a good idea to drill holes in the floor pan, but spose it would be ok if you don’t hit anything and paint the hole first to reduce rust. I think I would use pop rivets instead if you can get in there. Sheet metal screws will have a tendency of vibrating loose and end up in my tire. See the post on gas tank leak for what can happen drilling holes.

Thank you for the suggestion.
Is there any glue-like stuff I can use to bond the heat shield to the bottom of the car? How about plumber’s epoxy or JB Weld stuff?

Are you talking about the heat shield over the catalytic converter or the larger protective shield, the belly pan, that is used to keep water and crud from being thrown up into the engine?

Taint no glue gonna hold it. Also, they are usually stainless which will be a bear to try and drill through.

Bing You beat me to the gas tank leak comment. This project sounds like something that could easily be buggered. Maybe a good body shop should be consulted.

I doubt glue will work for any length of time. A drill/pop-rivet solution might work, but you’d have to take steps to prevent corrosion. And not leave any open holes in the floor pan that hot exhaust gas might use as a path to rise into the cabin.

If I had this problem, rather than guess, I’d at least consult my local inde machine shop or auto body shop (during a time when they aren’t busy) and show them the problem and ask for suggestions. Offer to buy them a cup of coffee and a donut. Someone there will likely offer up an idea, including part recommendations.

I’ve generally found the staff at these local shops, in approached in a friendly manner, are happy to offer suggestions, as long as it is clear from the outset they don’t actually have to do the job, or take responsibility if it is done incorrectly.