Monday, March 7, 2016

Underhood Parts: Painting Vs. Powder Coating

After a fruitless search for the "right" air cleaner assembly for my '76 Corvette, I've decided to go back to basics and use the factory unit.

I tend to favor more of a stock look under the hood, and GM engineers did a pretty good job of directing cool air into the carb via a plastic plenum, mounted above the radiator core support, and fed to the air cleaner assembly—and carb—via an air intake flex hose.

Originally I thought I'd just take it to a body shop and have it spray painted, but paint can (and will) chip, especially on parts that need to be removed from time to time in order to service the vehicle. So I quickly decided to have the air cleaner assembly powder coated to ensure durability.

I wanted it to look as close as possible to the factory finish which, as my research indicated, was somewhat of a glossy deep black. Upon my arrival at Advanced Powder Coating in Longwood, Florida, I realized that not all blacks—or any other color, for that matter—are created equal.

In order to keep the parts looking as OEM as possible, I narrowed my color selection to three options:
  • Semi-Gloss Black
  • Black Pearl
  • Gloss Black

I decided to go with Black Pearl, which although shiny, was not as glossy as the Gloss Black alternative.

Glad to say that it was the right decision as the finished product looks perfect!




But GM air cleaners of the era can be a bit complex, and mine included a hot air vacuum diaphragm valve, a hot air flap, damper door, and hot air inlet stove pipe. All those components are connected to a vacuum-operated temp sensor inside the assembly, connected through a vacuum hose.

Needless to say, plastic or rubber cannot be powder coated since the process involves heat, so they had to come off before being coated.

And even though I will not use the stove or any related parts, I still wanted the air cleaner to have the look of a stock unit. Having said that, the hot air vacuum diaphragm would not be able to be powder coated since it is a sealed unit with rubber bellows inside, so I had to spray paint it instead. A small compromise that looks just as good.

The rubber seal between the air cleaner lid and base was also removed beforehand.




Since the hot air vacuum diaphragm is held by a spot-welded strap, that I also wanted powder coated, I carefully broke the welds and sent it in to be coated. But before doing so, I drilled a couple of small holes in one end, so I would be able to rivet the strap in place, after securing the front tab. When I reassembled the air cleaner, a couple of black paint drops boated the rivet heads perfectly.

All openings were sealed properly, and I made an aluminum plate that I pop-riveted to the hot air intake hole after removing the pipe. The aluminum seal plate was powder coated since I attached it before I took the parts to the shop.



Advanced Powder Coating made a beautiful job of bead blasting all parts before they were coated, and they powder coated everything inside and out.

The square hole is for the filter that is connected to the right valve cover breather tube. The two small holes next to it are for the vacuum-operated temp sensor.



And here's the (almost) finished product.

All I have to do now is attach a new (repro) GM decal to the left side of the bottom assembly and connect a new fuel line to the pump, and she's ready to go back in the engine bay.