Here are some photos of the rust fix on my 85 GSL. This is what I did.
1. Knock out the rust with a hammer
2. Use a scraper to get out the loose stuff
3. Wire brush to remove crud and rough up the paint
4. Cut sheet metal to fit (I used a piece that had mastic on one side, left over from around the stove. This made it pliable and white (see photos)
5. cover the hole area with epoxy resin, then sit in the sheet metal pieces with short metal screws (work better than rivets).
6. fill from the outside with bondo, I used the stuff with fiberglass in it, a pain but I think it is stronger.
7. primer and undercoat
Passenger side on the next post.
Ray

 

the pic isn't workin ray

 

Shoot, I can't get this to work. PM me your email address and I will send it by email.

Ray

 

broke_ass_rx7_owner@yahoo.com ill get them up if its not the club server acting up.....

 

hmm doesn't sound very safe. you may have patched the hole and stopped any water from entering the car but the metal you have attached won't really be taking any stress like the orginal panel would have.

Plus if you have not cut all the rot out it will continue to rust underneath your patch till that falls off too.

The best way to repair a hole like that is to cut out till you find good solid metal and then seam weld new metal back in. + don't forget its double skinned so you need to repair the reinforcing plate too.

Mike

 

double skinned ..... and that is precisely why this part of the car get's destroyed. Mazda didn't have the technology at the time to properly seal the gap between the layers so water wouldn't get between them.

 

Your concerns are well founded, certainly this kind of patch up doesn't work on structural stuff or if any residual rust gets covered back up, only to rust again. However, in this case the rust holes didn't affect any structural steel and I was able to clean out virtually all the rust and get down to clean metal. The key is to infiltrate between the metal pieces with epoxy resin or bondo, so the water has no place to go. This is apparent in the photos, but I can't get them to post - badass RX7 said he might be able to do it. Anyway, I have done this kind of thing on other cars and depending on the circumstances the repair is good for many years - I haven't seen one go bad yet.
Ray

 

There are HOLES in the outer wheel wells that let the water in. I don't know what they were for but they are the reason for the rust.

 

Yes that's a good point.

Newer cars don't rust like that because parts like these are laminated together. The laminate (epoxy?) doesn't allow water to get between the parts.

For 1st gens that aren't completely rusted through yet I wonder if there is a way to seal that up. Perhaps dribbling or forcing something like POR-15 into the holes might to the trick. POR-15 is very thin and that just might work. Wadda ya think?

 

The hole are for the rear seat belt mounting bolts. And they still rust with seat belts fitted. Its like inittab said, the double skin is the real problem.

Ray,
you say the inner arches aren't structural, but why did mazda put a re-inforcing plate on them ? and the mounting for the lower link mounts in that area too.

Mike

 

Yes that plate does look like it is in there for structural reasons. Fortunately, in my case at least, the rust holes were right in the middle of the plate, leaving the periphery, with the rolled edge, in good shape. So I think the even with the rust and now with the repair they are still functioning structurally. Wish I could post the pictures, maybe tonight I'll try again. Thanks for the feedback on this, and of course if my car splits in two while I'm cruising down the interstate, I'll let you know!

Ray

 

The holes let water in, the double walls keep it there. There are double walls all the way around the back wheel wells but they only rust where the water sits. If the holes didn't let water in, most of these car's wouldn't rust.

What cars use epoxy in double wall spaces? Epoxy was around long before 1979.