Headlight "Doors"

[Dr.Jeff]

I am working on a custom modification to the headlight doors and came across a couple of issues.

One of the existing (original) doors had a bit of damage to the aluminum casting along one edge. It's a small dent or crease upward (away from the car) that caused a tiny crack in the cast metal. I assume the door was closed with something in the way (perhaps a tool or such) and the force of the door motor (which is great) actually bent the cast door over the object. I removed the doors to do the mods and attempted to straighten out the damage first. However I was not able to get it as nice as I'd like so I will use a spare door.

That brings me to the second issue. The spare door is from a rusty X that I bought as a "parts car". The factory paint has lifted from most of the door due to oxidation of the cast aluminum underneath. We've discussed this before, it seems to happen often. However I don't recall anyone describing a effective method of prepping the door prior to repainting, to avoid further paint lifting. Obviously I will strip it but I'm not certain what is the best treatment to avoid more problems. I know some acids work excellent as aluminum cleaners/polishes. Traditional sanding, cleaning and priming before painting seems normal. But is there any specific pre-paint treatment for these cast aluminum doors?

And there's a third issue. I found the replacement door did not fit my car well. The two doors (original and spare) appear to be identical. But when the replacement was mounted it had a slight interference with the hinge mounting plate on one side. I had to grind some aluminum off the door to allow it to clear nicely. I can't see any reason for the difference, why one door works well and the other doesn't. One is off a '79 US spec X and the other a later model Bertone spec. Perhaps there were minor production differences during the years in between.

 

[dllubin]

The paint on my doors separated from the aluminum at the trailing edge. There was a white powder between the paint and the aluminum. This is on a car that has had a roof over it for almost all of its life. I have a feeling that Fiat did not use the correct process for prep and priming.

 

[kmead]

I don’t believe the doors are aluminum. They are likely zinc alloy. What you are describing sounds like zinc oxidation.

Do the best of my knowledge there isn’t a welding process and because zinc is so crystaline you often can’t bend it back without cracking it.

Over time they have to make new tools. The 79 could have been from the last of the old tooling and the other from a new tool which would have different tolerances from when the tool was built. This isn’t too unusual in industry, in addition they may have made some intentional changes for the later cars to deal with another issue we know nothing about.

 

[JimD]

I don’t believe the doors are aluminum. They are likely zinc alloy. What you are describing sounds like zinc oxidation.

I thought I recalled the same Karl, that the shells were pot metal or something similar. So I checked MWB and their listing says the headlight shells are aluminum.

 

[jimmyx]

Traditional sanding, cleaning and priming before painting seems normal. But is there any specific pre-paint treatment for these cast aluminum doors?

Sand all the old finish off with a DA with a medium grit and finish with fine paper. Wash the door with Dawn or similar. Blow dry and wipe down with a paint prep solvent. Spray with 2K primer. The key is to prep the doors and paint them right afterward. If there are sanding scratches visible after the 2K you can spray over the 2K with high build primer. Everyone used to use self etching primer back in the day, but 2K is the weapon of choice and compatible with all modern top coats.

 

[Dr.Jeff]

Sand all the old finish off with a DA with a medium grit and finish with fine paper. Wash the door with Dawn or similar. Blow dry and wipe down with a paint prep solvent. Spray with 2K primer. The key is to prep the doors and paint them right afterward. If there are sanding scratches visible after the 2K you can spray over the 2K with high build primer. Everyone used to use self etching primer back in the day, but 2K is the weapon of choice and compatible with all modern top coats.

Thanks, that sounds like what I'd expect, a rather standard process. Given the propensity for these to sluff off the finish I thought maybe there was some sort of special prep treatment like exists for some other substrates.

 

[Dr.Jeff]

In the past I also thought these doors were some sort of cast "pot" metal due to their weight. However they are quite light once everything is removed from them. And after I stripped off all the old finish it has the appearance of cast aluminum....albeit a cheap quality one.

 

[tony x19]

I am working on a custom modification to the headlight doors and came across a couple of issues.

One of the existing (original) doors had a bit of damage to the aluminum casting along one edge. It's a small dent or crease upward (away from the car) that caused a tiny crack in the cast metal. I assume the door was closed with something in the way (perhaps a tool or such) and the force of the door motor (which is great) actually bent the cast door over the object. I removed the doors to do the mods and attempted to straighten out the damage first. However I was not able to get it as nice as I'd like so I will use a spare door.

That brings me to the second issue. The spare door is from a rusty X that I bought as a "parts car". The factory paint has lifted from most of the door due to oxidation of the cast aluminum underneath. We've discussed this before, it seems to happen often. However I don't recall anyone describing a effective method of prepping the door prior to repainting, to avoid further paint lifting. Obviously I will strip it but I'm not certain what is the best treatment to avoid more problems. I know some acids work excellent as aluminum cleaners/polishes. Traditional sanding, cleaning and priming before painting seems normal. But is there any specific pre-paint treatment for these cast aluminum doors?

And there's a third issue. I found the replacement door did not fit my car well. The two doors (original and spare) appear to be identical. But when the replacement was mounted it had a slight interference with the hinge mounting plate on one side. I had to grind some aluminum off the door to allow it to clear nicely. I can't see any reason for the difference, why one door works well and the other doesn't. One is off a '79 US spec X and the other a later model Bertone spec. Perhaps there were minor production differences during the years in between.

I sand blasted mine ,got all the paint and corrosion off in all area’s, then epoxy prime , then high build 2k primer .

 

[Longitudinal]

Unpopular opinion: paint can't peel off them if they aren't painted. Has anybody here polished the aluminum buckets instead of painting them? Bad idea?

 

[dllubin]

I suppose they could be anodized as well.

 

[Dr.Jeff]

I sand blasted mine ,got all the paint and corrosion off in all area’s, then epoxy prime , then high build 2k primer .

I've considered blasting it. I'll see how things look with some sanding first. But the cast is really porous so it might need something more aggressive to really get all of the oxidation out of the pits. Either blasting or possibly some acid treatment.

 

[RUDYKYX19]

I am working on a custom modification to the headlight doors and came across a couple of issues.

One of the existing (original) doors had a bit of damage to the aluminum casting along one edge. It's a small dent or crease upward (away from the car) that caused a tiny crack in the cast metal. I assume the door was closed with something in the way (perhaps a tool or such) and the force of the door motor (which is great) actually bent the cast door over the object. I removed the doors to do the mods and attempted to straighten out the damage first. However I was not able to get it as nice as I'd like so I will use a spare door.

That brings me to the second issue. The spare door is from a rusty X that I bought as a "parts car". The factory paint has lifted from most of the door due to oxidation of the cast aluminum underneath. We've discussed this before, it seems to happen often. However I don't recall anyone describing a effective method of prepping the door prior to repainting, to avoid further paint lifting. Obviously I will strip it but I'm not certain what is the best treatment to avoid more problems. I know some acids work excellent as aluminum cleaners/polishes. Traditional sanding, cleaning and priming before painting seems normal. But is there any specific pre-paint treatment for these cast aluminum doors?

And there's a third issue. I found the replacement door did not fit my car well. The two doors (original and spare) appear to be identical. But when the replacement was mounted it had a slight interference with the hinge mounting plate on one side. I had to grind some aluminum off the door to allow it to clear nicely. I can't see any reason for the difference, why one door works well and the other doesn't. One is off a '79 US spec X and the other a later model Bertone spec. Perhaps there were minor production differences during the years in between.

hi jeff, try professional marPRO Zinc cromate in green or yellow as a primer/base for your paint. we use it on our aircrafts even here in the corrosion prone carribean and it works excellent. provided the base aluminium/alloy is prepared well, no grease, dirt residue etc. you might use MEK for cleaning as well. good luck

 

[Dr.Jeff]

Unpopular opinion: paint can't peel off them if they aren't painted. Has anybody here polished the aluminum buckets instead of painting them? Bad idea?

As I was doing my mods to the door, including cutting and grinding, I realized the casting is very porous and rough. So I'm not sure if they could be polished? I've done a bumper delete and smoothed the nose of the car to cover the huge pinch weld and fill all the holes. Therefore I prefer to keep the headlight doors body color to blend in with the overall shape of the nose for a 'clean' look.

 

[Dr.Jeff]

hi jeff, try professional marPRO Zinc cromate in green or yellow as a primer/base for your paint. we use it on our aircrafts even here in the corrosion prone carribean and it works excellent. provided the base aluminium/alloy is prepared well, no grease, dirt residue etc. you might use MEK for cleaning as well. good luck

Thanks Rudy, I haven't heard of that product - I'll look into it.

 

[Dr.Jeff]

There was another issue related to the headlight doors I forgot to mention earlier. The large pivot bolts on all of mine had some damage to the threads. It was more than the usual "stuck" fastener, but actual thread distortion. I had to chase the threads for the bolts as well as the welded nuts they go into. My guess is the side to side ("sheer") forces each time the doors are moved up or down by the motor put stress on those threads. Those electric motors have a lot of torque and when the pivot bushings get dry and dirty there's a fair amount of resistance. The load must go somewhere. After cleaning everything, repairing the threads, and making sure things were aligned correctly, the doors operate MUCH better.....and that is without any lube yet (waiting until the paint work is done before adding lubricants to the moving parts).

 

[Longitudinal]

As I was doing my mods to the door, including cutting and grinding, I realized the casting is very porous and rough. So I'm not sure if they could be polished? I've done a bumper delete and smoothed the nose of the car to cover the huge pinch weld and fill all the holes. Therefore I prefer to keep the headlight doors body color to blend in with the overall shape of the nose for a 'clean' look.

I hear you. Somebody must have done it at some point, but I have never seen any pictures. The pores can be filled through careful application of a TIG torch, but then the filler material will have a luster different from the base material when polished.

It's just a goofy idea. I probably wouldn't do it.

 

[Dr.Jeff]

I hear you. Somebody must have done it at some point, but I have never seen any pictures. The pores can be filled through careful application of a TIG torch, but then the filler material will have a luster different from the base material when polished.

It's just a goofy idea. I probably wouldn't do it.

As you say, someone must have tried at some point. I recently noticed a X with the headlight rings ("bezels") chromed:

 

[Dr.Jeff]

we use it on our aircrafts even here in the corrosion prone carribean and it works excellent

I imagine rust is a major issue where you live. Having lived on the ocean front most of my life I'm familiar with the effects of the salt air. I read where your X had been stored in a open carport for several years. Given the X's susceptibility to rusting, how badly rusted is it?

 

[Dr.Jeff]

Yet another issue I forgot to mention. The three little screws that hold the outer trim ring onto the face of the door tend to seize (dissimilar metals) and snap off when trying to remove them. I had to drill out most of them. And that isn't easy because the surrounding aluminum is very soft and the screw shank it fairly hard. So the drill bit tends to walk off the screw and go into the aluminum creating a uneven/non square hole. Eventually I got them drilled out, reamed the holes, then re-tapped them for a larger thread size. I'll use stainless machine thread screws instead of the sheet metal thread ones from the factory.

 

[Dr.Jeff]

I sand blasted mine ,got all the paint and corrosion off in all area’s

Tony, I've decided I'll blast mine as well. The top surface is pretty flat and can be sanded easily. But the rest of it has too many contours, cast brace structures, pockets, etc, to sand. And I'm finding the corrosion is over the entire surface of the whole unit. The more I remove the existing paint the more I see there is oxidation under it. So this is definitely a issue with improper prep before the factory finished them. Like pretty much everything on these cars, the headlight doors are turning into a bigger project than I imagined.