Date: Wed Dec 4 21:17:20 1991   
Subject: repair advice needed

    Date: Mon, 2 Dec 1991 16:01 EST
    From: greeven%speedy.clipper.ingr.com@mathcs.emory.edu (John Greeven)

    Well, I've finally gotten back to my z-project.  I'm trying to decide
    how to best approach my problem.  I've got a pretty badly banged up left
    rear quarter panel on a 1970 240z.  It's half way to being strait but
    I'm wondering if I wouldn't get better results by cutting off everything
    from the top of the fender wells down and replacing it with a metal
    insert.  Anybody been through this?

    BTW, I plan on selling the car after the repair so that I can finance
    a race car.  

    John Greeven
    greeven@clipper.ingr.com

You can go either way.  Both can come out essentially perfect, depending on
your bodywork skills -- and particularly what you're best at.  
In principal, replacement is better, but I'll describe both and you can
compare. 

But first, my story: I've redone a '75.  I took an evening body shop
class at our local community college.  It took 4 semesters till the car
was painted!  Highly recommended if available, unless you're already
completely secure with the stuff (which you aren't or you wouldn't 
ask :>) and you've got scads of body tools.

Anyhow, I welded in a couple of patch panels to unrust it.  
And I encountered a minor horror with the left rear fender;  The lady
I bought the car had had some body work done on it. It had been banged
in.  The shop (a _real_ body shop, mind you) used a slide hammer to get it
sort of in shape, then glopped bondo on (up to 3/8" thick!) and sculpted
it back to (temporary) perfection.   WRONG!

Hammer & Fill route:
  The thing is they were apparently put off by the Gordian knot of the
interior panels.  You've got to take 'em out (ultimately all of them!)
if you're going to hammer the fender back straight.  The less straight
you hammer it, the more bondo you've got to use to fill it.  And unless
you're truly expert with a torch and hammer (ie. to shrink the metal
which is stretched at the kinks), you _will_ use _some_ bondo.   That's
OK, just not too much. You can do a decent job without a torch, you just
hammer & dolly till it's as close as possible to original (but _below_
the original level) then fill.

Getting the bondo straight is the trickiest part of this operation.
You really have to develop a feel, literally, for what is smooth and
straight.  That's where a class helps.  And there's various tricks:
spray a light coat of contrasting paint (a "guide coat") , then lightly
go over it with a body file.  This tells you where your high & low spots
are.  Otherwise you cant see 'em, and you'd be surprised at how bad some
things you cant feel look when you've got the finish coat on!
So you file the high spots down, fill in the low spots again and repeat
(and repeat......)

Patch panel route:
  First rule is get real patch panels, making them out of sheet metal
stock is usually tough.  You can get 'em from places in the monthly
posting, Motorsport for example.  So the first comparison between
methods is $ vs. time!   You still oughta take the interior panels out.
(get some of those wonderful plastic rivets while you're ordering the panel)
You get the panel and _then_ mark and cut out
the old, leaving maybe 1/2" overlap.  You can get cute and flange it:

               weld her
                |
  old  ________ V__________ new
               |_______
There're tools to do this easily.
Now you grind the bead of the weld flush and use bondo to fill it in --
but it should take very little.

OK, if you're good at sheet metal welding, this is the best and fastest.
But if you're not quite that good it's the same!  It is surprisingly
easy to warp large sheet metal panels, even with a MIG.  Note that you
dont get outrageously wavy metal, you get long shallow waves that you
might not notice at first.
If you've got strength but little finesse, you can easily hammer a
crushed panel to approximately the same correctness as you can 
warp a new panel by welding!  If you warp it, you go back to phase 2 of
the hammer & fill route.  Even if you're a good welder, I'd recommend
using the guide coat to verify the straightness.

So, in the case of rust, you've got to put new metal in.  For dings, its
a bit of a tossup.

... hmm, got a bit long.  let us know how it goes.

bruce
miller@cam.nist.gov