Polymer Eliminates Mainfold Leaks on Vintage Motorcycles

Bruce Argetsinger, CEO and owner of Mold Threads, Inc., (MTI), a custom molder, races vintage motorcycles in his spare time. While compet...


Bruce Argetsinger, CEO and owner of Mold Threads, Inc., (MTI), a custom molder, races vintage motorcycles in his spare time. While competing on the flat track racing circuit, he saw riders replacing leaking intake manifold seals made of brass with seals made from Victrex PEEK polymer. As an injection molder, Argetsinger knew that the polymer was the best material choice for the application. "I realized that MTI could injection mold the seals at a much lower cost. We build our own molds and have been molding complex components from Victrex PEEK polymer for years."

Argetsinger described the market for replacement components for vintage motorcycles as "huge" and not limited to flat track racing. "There are thousands of owners around the world who need high quality affordable parts in order to restore these antique machines," he said. "By injection molding the Victrex PEEK polymer, we've been able to offer affordable intake seals that eliminate manifold leaks. Seals made of brass are notorious for leaking. They were factory installed on Harley Davidson and Indian motorcycles built between 1932 and 1965 and need to be replaced each time the engine is re-built."

Argetsinger explained the function of the seals, "They are located on the manifold and when the piston goes down it actually creates a vacuum that sucks an air fuel mixture in through the carburetor.  The seals are actually between the carburetor and the cylinder itself so if there is a leak it sucks in extra air. This additional air causes a lean mixture, which is a mixture that's got more air in it than is actually required for actual combustion. If the mixture becomes too lean (approximately 14 percent fuel to air) it burns a lot hotter. A hot burn can cause a number of problems including seized pistons, bent rods and even destruction of the engine."

What makes the polymer a great option for intake seals is its 260 degrees C (500 degrees F) continuous operating temperature said Argetsinger. "I've done some tests on the temperature in this area and it's up around 135 degrees C (275 degrees F)," he said. "PEEK polymer retains its mechanical strength at these high temperatures and doesn't tend to push out of the area when it's under compression. Some materials will actually creep or "cold-flow" when they are under constant pressure. PEEK polymer does not. Another very important feature of the seal is that, unlike brass seals, it is re-usable."

Injection molding the intake seals for vintage motorcycles is just a sideline for MTI. "We mold the intake seals in our slow time," explained Argetsinger. "We make all three different sizes for the vintage Harley Davidson motorcycles and three for the Indian motorcycles. The owners tell us they won't use anything else." 

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