Tuesday, January 18, 2011

Cowl Panel Replacement - Episode 4: Divide and Conquer

After weeks of planning and prep work, I felt confident I had a plan put together to get the new cowl installed with professional results.  With the inner kick panels repaired and the flanges and saddles straightened and tidy, I spent several days getting the new cowl to fit as perfectly as I could manage it.  I venture I had the cowl in and out for trial fitting at least a dozen times over the course of things, and every time the fit got better and better.  Once I was satisfied that the parent sheet metal was in as good a shape as it could get, I treated everything with another dose of phosphoric acid and shifted my attention to a number a small issues that required attention on the cowl itself.
As I have come to learn quite clearly through the course of this restoration, even the best of panels is rarely ready to go out of the box, and this cowl was no exception.  However, while I have had many reasons to rail against several of the Dynacorn repair panels, this cowl was indeed very good from the off.  All told, only minor tweaks were required to get the cowl into shape for final fitting and involved little more than a bit of grinding here and there.  Particularly, the passenger front corner had a flange intrude into the upper flange area where the cowl end enclosure mates to the upper cowl panel.  This only became evident during the final part of the fitting process when I made sure the end enclosures would fit well with the new cowl.  I had a devil of a time trying to understand why the passenger end enclosure simply would not fit properly no matter what I did.  After a bit of noodling on the matter, I discovered the intrusion of this small flange and after a very quick swipe with my new Makita 4” grinder, the issue was completely resolved and the end enclosure suddenly fit absolutely perfectly!
With everything now exceeding my expectations for fit and finish, I prepped the flanges of the new cowl by drilling the plug weld holes with my Blair rotabroach and deburred everything with my trusty angle grinder.  With that completed, I taped off the cowl and firewall flanges and sprayed them with SEM #40783 Copperweld weld-thru primer.  I have found I like this product much better than the 3M weld-thru primer I have been using.  SEM Copperweld covers better and seems to reduce weld spatter better than the 3M product at a very competitive price.  And best of all, my local paint supply store, GNE Paint Centers in Lake Orion, MI, has it on the shelf.
Once the Copperweld primer dried overnight, we carefully placed the cowl in place, and using a pair of large drifts to realign the panel in its precise location, I buckled the whole works down using my high clamp force clecos and a variety of vice grip pliers and welding clamps, exactly as I had done when doing all of the fit work and preparation steps before.  Fortunately, I was rewarded with exceptional repeatability of the fit I had worked so hard to achieve and I was ready to weld the cowl in for good.
Welding in the new cowl required a bit of strategy to ensure the whole works didn’t move during installation.  First, I decided it was best to anchor the panel at each end and then move to the middle section of the front firewall flange to finish the job.  Although this meant that the most difficult welding operations were first on the menu, it ensured the fit was precise and no warping of the panel could occur.  I started by carefully welding the saddles in place from the bottom (an absolute B*TCH of a job).  Recall in my earlier ramblings that this cowl, as a one-piece assembly, could not be installed as it was from the factory and therefore the saddles must be welded from the bottom to ensure proper installation.  For the approximately 20-odd welds the saddles required, I had to invest about an hour per side contorting myself into all manner of unspeakable positions to get these saddles ready for primetime.
Next, I tackled the upper flanges at the ends of the cowl where they meet the A-pillar bases.  At this point, my ancient MIG welder decided to go menopausal and fight me most of the way.  After a few choice words and LOTS of manipulating of settings, I managed to get both ends welded up, albeit with more metal deposition than I like.  Oh well…….more friggin grinding.
At this point, the cowl is very solid in the car and the front firewall flange looks better than it ever has……and I hadn’t even welded it up yet!  Whooohooo!!!  With a second wind in my sails, I marched across the front of the cowl flange starting in the middle and working my way out to each end.  I bracketed each weld with welding clamps to ensure the flange fit was extra tight and was rewarded with an absolutely fantastic looking flange when done.  Finally, I removed all of the clecos and clamps and went back over each cleco hole with the Blair rotabroach and opened up plug weld holes.  After a few minutes welding, the cowl was completely welded in and looking tight and right.  The following day, I ground every weld down as I had done so many times before.  After a few hours, the flanges looked superb and the fit was truly exceptional.
Next on the agenda, I will coat the inner cowl boxes with an application of Zero Rust coating, blast the cowl end enclosures and prepare them for welding back in, fit and weld the cowl to apron braces and weld in the fender mount tabs to complete the job.  Oh yes……..and prepare my tax return so I can invest in a new inverter-style MIG welder!  A lot of work left before this cowl adventure is complete to be sure, but what remains is comparatively a walk in the park.  Off I go…….
After final fitting of the cowl end enclosures, everything was swabbed in phosphoric acid again to ensure a good bonding surface.

Firewall flange was repaired and straightened as part of the fitting process.  Here, it has been coated in phosphoric acid in preparation for weld-thru primer.

Inner kick panels were repaired and prepped for final cowl installation.  Note the nice, straight cowl saddle.  These outer kick panel surfaces will be coated in Zero Rust coating before being buttoned up with the outer cowl enclosures.

This little bugger took me a few days to figure out.  The part of this small flange (painted yellow) on the passenger side front of the cowl saddle prevented the cowl end enclosure from fitting properly.

A few seconds with a body grinder and a clean-up with the sanding disk and the end enclosure fit absolutely perfectly!

I marked each plug weld hole with a paint pen to make it easier to identify where I needed to drill.  Notice the plug welds are placed between the factory spot welds.  While this may not be concours correct, it ensures the integrity of the panel and minimizes any structural problems with the assembly once it's welded in the car.  Since the plug welds will be invisible and the spot welds will remain, it will be virtually impossible to tell the cowl is not installed with factory spot welds.

A quick shot of the driver cowl saddle drilled for plug welds.  This part of the cowl must be welded from the bottom due to the design constraints of a fully assembled cowl.

SEM #40783 Copperweld has become my favorite weld-thru primer.  Excellent stuff, but pricey.

Driver side cowl saddle primed with SEM Copperweld

Passenger side saddle primed.

Here, you can see the cowl panel end has been taped and primed with SEM Copperweld after the flanges have been drilled and deburred for plug welding.

Final fitting begins with a pair of large drifts inserted into the cowl brace bolt holes.  Once this is done, a series of clecos and vice grip pliers and welding clamps are used to secure the cowl for welding.

The ends of the cowl are welded first to lock everything down.

The outer ends of the firewall flange are plug welded and tie everything together such that I could move on to the center firewall flange.

With the firewall flange completely welded, the cowl is now an integral part of the chassis structure once again.

Welds are ground smooth and brushed in preparation for a sealing coat of primer.  Here is the driver side......

and here is the passenger side after grinding.

The fit was absolutely superb.  Here is the passenger side top corner showing the fit between the cowl on top, the firewall and the inner kick panel at the lower saddle flange.

Here is the passenger side upper saddle flange fit viewed from the inside.

The driver side upper saddle flange area as viewed from the inside.

And finally, the passenger side top front corner showing the cowl on top, the firewall and lower cowl saddle area.
While there is still a lot of work that remains before the cowl project is complete, the results look good and the rest of the work in this area is comparatively easy.


  1. The fit is amazing! Outstanding work once again Sven!

  2. Thanks Alex! I was definitely NOT disappointed in the fit and overall quality of this piece (*big sigh of relief*)