When It Says Cut Out the Rust ...

[Morrisman]

Should we say that it is probably unwise to remove the entire red-lined section in one go? If you do so, you lose all reference points. Maybe cut out a bit at the front, insert, line level and tack patch and then move along to the next section. It all ends up as new metal but not as one huge piece.

As a (once) enthusiastic amateur I’d make the whole patch panel in one piece, including the top surface and the upright flange bit, then cut the old metal out. The patch panel should locate well enough at each end to ensure everything else stays in the correct location.
How well it works in practice is a different story though….

 

[cobolman]

If that's what is under the primer I would be concerned about the quality of the blasting done. I would expect to see clean pitting, not rust filled divots.
Also what primer was used?

Primer: MIPA Epoxy 2K

 

[cobolman]

Appalling blasting, did they say what grade they would blast it to? That panel is eaten at least halfway through and if done properly would have a fair number of holes.
Cut to the red line except where the spot welds are on the far right.
At least you have started right way by blasting, had it been done properly any welding would have been easier. Suggest you sand off any other rough areas, they may have covered up other issues with primer.

Good tip. I will now be taking any frilly areas back to steel so I can assess what it's like before attempting to weld / replace.

 

[cobolman]

Before doing anything go around the rest of the shell and make sure you identify all the areas that need attention - most of my new projects come with a few sections that need welding...
I have fitted new panels but prefer to patch repair, personal choice but often because I'm working on cars where panels aren't available, I recently fitted new pattern floors in a project and "fettling" took a lot longer than I was expecting.

Depending how confident you feel :
Change the right hand end of the red line above so it follows the row of spot welds but stops a couple of inches before the bulkhead (easier to tidy the weld from both sides)
Mark out the red line using a straight edge before cutting (much easier to fit the new piece)

Before you remove the rusted original section :
measure key dimensions (from the top of each inner wing vent to the top lip) so the new panel goes back in the same place
make up as much of the replacement piece as possible (leave a decent overlap to trim later).
My latest tool is a die grinder, great for tidying welds where an angle grinder won't reach - ie your the under bonnet weld near your bulkhead.

Thanks for some great tips, Nomad.

 

[bert]

I've ordered front repair sections from M-Machine. I was loath to do this as it's a 1960 Mk 1 Mini and I wanted to keep it as original as possible. But as the many responses on here indicate, sometimes the steel is just too far gone.

ps: I've also ordered new front wings and front panel because, as you point out, a complete front end is almost always needed.

My experience is the m machine parts don't really fit great. I almost exclusively used heritage parts as they use mostly the original tooling

 

[jo1010]

Just an aside as an example of how a commercial outfit might leave things....soundtrack included things like we're a professional repairer using BMW approved products...years of experience repairing BMW's blah blah....So they look at the peppered and holed through inner sills on a z3....treat with POR15....and declare it fit for paint ....because "the rust has been stabilised". IMO just WOW . I wouldn't want to spend £4 k with these guys for that kind of approach. It's holed through ....just cut it out and it's then good. Unbelievable!.
The whole link is here if you fancy a look at z3's - that sill bit is around 16 mins in the video

 

[dave h 2]

That is what sensible people would call a colander and extending the crumple zone to include the soft squidgy bit that drives.