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Stainless Steel Fastener Use with Carbs?

Once in a while I get a question about stainless steel fasteners and why I don't include them in my kits or offer them as an option. The short answer is that I'm in the business of helping people solve their carburetion problems, not to create new ones. If you like the bling aspect of stainless steel fasteners, then consider this.

Stainless steel makes a great looking fastener. The fact that they don't rust is another plus. However, I don't recommend their use in vintage Honda carburetors. Here's why...

The main reason is mechanical. Commonly available stainless fasteners often are socket screws such as these:

These fasteners are typically installed with wrenches such as these:

These wrenches allow far too much leverage, especially in the hands of amateur mechanics. It is very easy to strip the delicate small threads in carb bodies with these over-leveraged wrenches. The 4mm float bowl screw threads are especially susceptible to such damage. Once so damaged, the carb body must be repaired with the installation of Time-Serts (preferred), Heli-coils or the like. A tedious and highly unnecessary task!

The second reason relates to differential electrode potential compared to the aluminum alloy which forms the carb bodies. This fact can encourage galvanic corrosion (oxidation) which potentially can seize fasteners over time. Of course, any fastener (of any type) can seize given the right conditions, but Honda specified zinc and cad-plated fasteners for a reason...not just cost savings. It is true that stainless fasteners are considerably more costly.

With a few exceptions, the preferred hardware for vintage Honda carb assembly work is zinc or cad-plated panhead Phillips screws such as these:

Similar to OEM, this is the type of hardware supplied in my various Master Carb Overhaul Kits. Not only do they look more original, they are safer to use. In my experience, amateur mechanics are also much less likely to strip threads when using a Phillips screwdriver as compared to a socket screw wrench.

However, some ham-fisted mechanics could probably strip the float bowl screw threads using their fingers alone! Remember, snug is all you need. The gaskets do all the sealing work...not the screws!

If you decide to use stainless fasteners against my advice, at least select fasteners with Phillips heads. Consider the application of a good anti-seize compound as well.

Thanks to Martin Jack of Hammel, Denmark for suggesting this Tech Tip.

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