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Noise Reduction

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mstull

R.I.P.
Joined
Jun 23, 2005
Messages
1,263
Location
West Texas
I read about this in a motorcycle magazine, decades ago. You cram little segments of rubber between the engine fins on the head and cylinder, to keep the fins from ringing. I have done this a couple times on previous engines. But it made the most difference on this MZ201 engine. It was so loud before, with a high pitched rattling sound, like someone beating on cymbals. It was hard to bear in the cockpit, even wearing a head set.

Now it just has a deep, powerful sound. It's hard to quantify without a sound meter. But I'd estimate the overall sound level is reduced by almost half... which is amazing, considering all the sound from the exhaust, carb intakes, and prop. And the remaining, deep sound is so much more pleasant, it actually sounds good.

I used little pieces of 3/16" OD by 1/16" ID neoprene tubing. Cutting them to the perfect length is touchy. But sometimes you can find a different home for a piece that's too long or short. You just cram them in there, and straighten them with a small tool, like needle nose pliers. They need to fit very tightly, to damp the ringing and stay put. It takes a good hour to do both cylinders and heads. It took almost 3' of the tubing (available at Aircraft Spruce for next to nothing.)

It's easy to tell if an engine will benefit from this, by just tapping on some fins with a small tool. Usually they work best if you put them on the corners of the fins. Longer fins on the heads got one on each end. Fins that don't ring much, when you tap on them, can get by with a rubber piece in every other gap. Newer motorcycles sometimes have cast-in joiners on the corners of the fins to keep them from ringing, to pass legal sound limitations.
 

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