Removing In-line Filter

[Cracker39]

After reading about the potential hazards of aftermarket in-line fuel filters, mounted using clamps and rubber gas line tubes, I decided to go back to the original fuel line on my indented firewall '31 Tudor. I've been driving the car a fair amount lately on rough roads, and the clear filter shows no contamination. The clear filter is a definite advantage in that respect and I'm hoping that this means the tank is relatively clean. That said, does the side-mounted sediment bowl on the carburetor do a good job of trapping contamination from the tank? I know that it was Henry's original design from the start (---sediment bowls) but I've also read a lot about aftermarket fuel filtration systems that others have installed.

[MikeK]

The side mount sediment bowl does a superior job. Being at the lowest point in the supply it is the correct place for separating water. The drain cock on the base makes it easy to occasionally flush. The internal filter screen is huge compared to other adapted types used on Model A's. Because the screen is vertical and so large there is not enough flow rate to hold any particles against the screen, they fall to the bottom from simple engine vibration even while running. The screen pore size is sufficiently small to stop particulates that could not easily pass and be flushed by the float valve or jets.

Some people feel the need to re-invent a well engineered wheel and come up with some interesting not so round designs. I get the biggest laugh from those that insist a much finer pore filter is required. While modern fuel injectors may indeed be compromised by 25 micron (0.001") particulates, large contact ring low seat pressure float needle valves easily tolerate particulates ten times that size. The original steel pins are best, various 'viton' elastomers prevail in the aftermarket and many are not so tolerant due to their lower surface hardness that may cause solids to embed.

So what becomes of the engine when it 'eats' those particulates? From the gasoline tank they are primarily hydrated ferric oxide (iron III oxide, AKA rust) and some litharge (lead II oxide, PbO) and a mix of both hydrated and metastable stannous oxides (pred: tin II oxide, SnO). The latter two a result of the Terne plate and solder decomposition in the presence of oxygen and water. All three are extremely low in hardness in either crystalline or amorphous form while en mass and do virtually no abrasive damage to the cylinders, rings, or valve seats. They reduce mechanically to polishing compounds and pass the rings into the crankcase oil. Since most people run Model A's without air filters and suck up silica dust from the road, which IS highly abrasive and in much greater quantity, the gasoline particulate fines become moot in the grand scheme of engine wear.

I could extend the discussion into vapor nucleation points resulting from fuel line flow transitions (added filters, etc.) between the fire wall and carb, but that would open up the entire dreaded vapor lock discussion. Everyone already knows testimonials trump science, so clothespins are the answer there.

[Cracker39]

Wow! What a great answer - and just the information I was looking for. Many thanks!

[Charles Coe]

In the side mount sediment bowl, the filter screen is horizontal vice vertical.

[MikeK]

Originally Posted by Charles Coe

In the side mount sediment bowl, the filter screen is horizontal vice vertical.

Yes it is! I have two late '31's. Getting dusty. Thanks for the correction. Still, I have never disassembled one and found that large cross-bolt cover screen clogged with anything. It all passes to the bowl bottom.

[Charles Coe]

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Yes, it does work very well. I've never found mine clogged either.