Special black paint for a carburetor ???

[KNUCK]

Anybody have an opinion on what black paint to use for painting a carb on my 46' Chief ? Is there a type that is less likely to be damaged by gas? I have heard from a friend to use Imron?

Please give me any good or bad results you have had.

[exeric]

Knuck, I painted the Schebler white metal carb on my '40 Chief with Imron and it is holding up well. Gas seems to have no effect on it. The bowl was painted with Centari and it's wrinkling here and there. When I first painted it I was concerned about the glossy finish but in the environment it occupies, it didn't take long to get dull.

[AdminGuy]

I receintly stripped down a black oil pump. It had a white base under-coat. My thought is that it was used to fill in the uneven texture of the cast body. Any thoughts as to what was used for this white?

Would a carb have a white under-coat also?

[T. Cotten]

A white undercoat on an Indian pump could have been precious (and toxic) cadmium. Paintstripper alone might have produced a museum-quality conservation.

Die-cast potmetal Scheblers (bare until mid-'35?) sported a thin gloss black as shown in this concerved original-paint DLX110 (attached).
It appears that even the cad bowl lid was painted.

I was subbing bodies out for baked Aerogloss over baked Variprime at great expense. However I have found that an equally fuel- resistant coating can be achieved with rattlecan VHT epoxy.

Pitting can be filled with J-BWeld, and sanded with great care. Many potmetal bodies have such condition that a satin finish if more aesthetic.

For silver, and touch-ups on nickle and cad, I use a fuel-proof isocyanate urethane, of which I believe Imron is a variety.

....Cotten

[KNUCK]

Great information. I knew the answer would come from within this site. I will try the VHT epoxy on a test panel and give it a test with some gas in a few days. Thanks-

[AdminGuy]

for it to set up properly you have to bake it. test on metal. Baked and not baked. You'll see.

Thanks C.

[KNUCK]

Thanks for the tip. I will be sure to read the instructions, contrary to what my wife always thinks.

[T. Cotten]

Warning: potmetal is technically a liquid. At higher temperatures it can become fluid, as a pass of the hone through this Four carb demonstrates: (attached)

220F seems safe.

....Cotten

[KNUCK]

I see the result of this over cooked carb. I will bake to the proper temperature.

Thank you Emril, I mean Cotten.

[swall]

NO! Pot metal is not a liquid at room temperatures. Most "pot metal" items are zinc alloy die castings which start to melt around 600F or so. In the jpeg, I see no evidence of melting--just some low spots in the bore that did not clean up with the hone. I have a degree in Metallurgical Engineering and have worked in the casting industry and know these thing

[T. Cotten]

Liquid.
Like old window glass slowly attempting to crystallize, and sagging over decades. Potmetal is by definition, the dross off the top of the pot of molten metal. Its composition rarely poured the same way twice.
As a random mixture of often incompatible metals, it remains fluid, although moving at a rate mortals rarely live long enough to observe.

Heat speeds it up, naturally.

More distortion attached. Note that the hole is not anything like round. Instead it looks like the carb was made of wax and left in the sun.

Thirty to forty thou out of round has been found on '38-'39 Four carbs, the worst for heat distortion.
It is such a prevalent problem for these models, that the value of a serviceable core has exceeded a more common model by tenfold.

With all due respect, Swall, your degree only taught you to see the short term of things. We are dealing with the cumulative effects of seven or more decades. And that's a blink of the eye, nay,... a nanofart in the dark,.. when compared to a geological process. However the molecules in our machines follow the those same rules of Nature. Dontcha just hate that crystal cleavage signature when a part suffers a catastrophic break!

Feel how heavy that potmetal is?
Thats lead (Pb).


...Cotten

[swall]

T.Cotton--I had another thought on this. As zinc alloys melt around 600F or so (I will look this up when I get back to work) the alloys will tend to warp at much lower temperatures. So, warpage could occur at the higher end of paint baking temperatures, say 400F. So, if warpage occurred in the bore, it would result in the non clean-up when honed, as your pictures show. Zinc die casting alloys, such as Zamak, contain around 4% aluminum and some other metals, depending on the specific alloy.
Zinc is more dense than steel, so yes, "pot metal" will feel heavy. These alloys are not very corrosion resistant, so some of the deterioration found on the edges of flanges could be due to years of corrosion eating the metal away. Metal alloys are either mixtures or solid solutions--but they are solids at room temperature (except for mercury). They are crystalline, which is one physical characteristic of a solid and this can be shown by x-ray diffraction. Yes, window glass is a liquid--a "supercooled liquid actually, and it does not have a crystalline structure.Your discription of the origin of the term "pot metal" makes sense, from a historical perspective.
But as long as die castings have been made, the metal is supplied as ingots of controlled composition and purity, otherwise the process just wouldn't work.

[T. Cotten]

Swall!

The composition of potmetal Schebs varies to an extreme.
Almost to where no two models are alike.

My welder associates must trial and error their way through a library of filler rods for each carb until one with can be found with any affinity at all. Some TIG up acceptibly; some won't even accept "Muggyweld".

The DLX80 and 81 models have proven the worst.

It is not unusual to find airhorn screw holes have moved, with the mouth of the carb appearing obviously oval. Manifold flanges are often dished to the naked eye. Bores are often constricted to where they must be honed so that even an original throttledisc can be installed, much less an oversized one.
Throttleshaft bushing bores are often no longer in line.
One of the most aggravating distortions that plague potmetal Schebs is when the meager pressure from the detente springs push the needles outward over decades, egging the needle bore to where it no longer aims at the seat. The stuff moves.

Venturis for most Schebs and all Linkerts were also potmetal, although the two used noticably different alloys.
Both suffer from shrinkage. Schebs are of course older, and also very brittle, presumably from crystallization. Linkerts can be swaged much easier, however they tend to shrink back over a period of months!

....Cotten

[swall]

Cotten--the distortion you have described is classic "creep" phenomenon of metals. Creep is metal movement at elevated temperatures due to stresses, either applied or residual. Castings contain residual stresses (locked in stresses) when they are cast and sometimes the casting will distort when machined. Other times it will not, but will eventually distort after long time exposure to elevated temperature. This long term distortation would be due to the original locked in casting stresses as well the applied stresses (stuff bolted on, spring loaded assemblies as you have noted, etc). So, where am I going with all of this scientific nonsense? Back to the original question--what is a safe paint baking temperature? The answer will vary depending upon whether the carb body is a zinc alloy casting or aluminum alloy casting. You have stated that the scheblers have varied. I would guess that prewar stuff tended to be zinc and post war stuff tended to be aluminum. Aluminum would not be a problem even with with a 400F paint bake. Zinc would be problematic at a much lower temp. It may be that it starts to move at tempertures lower than the max service temperature! In that case, the paint bake temperature will not matter, as long as it is lower than the operating temperature. Probably around the 220F figure you cited. As to your welding observations--there may be a simple chemical spot test that would alloy a zinc casting to be distinguished from an aluminum casting. I will look in to this if it would be of help.

[T. Cotten]

Swall!

There were no post-war potmetal Scheblers. (For production American motorcycles anyway, by all published accounts.)

Only G models even suggest that aluminum is a significant part of their unique alloy.
DLXs are boat anchors. Please hold one in your hands before further speculation by instinct.

And yes, spot testing info would be most helpful for the entire industry, and I encourage you to post it for us all. Often cad can only be distinguished from tarnished dull nickle by a drop of caustic, and a selective process for alloy compositions would be universally appreciated.

Meanwhile, even super-stable castiron *creeps* with fastener stress and combustion pressures. Potmetal runs like mud by comparison.

....Cotten