QUOTE (woody2shoes @ 19 Sep 2007, 06:04)
<{POST_SNAPBACK}>While servicing my clutch of Hornby 0-6-0PT's, I noticed that they ran much quieter with the body off. Contacted Hornby looking for a possible 'paint the body interior' solution. Hornby went into denial mode saying that nobody else had complained and their boffins could find no noise problems, yet all those I have shown the comparison (with and without), agreed that there was a noticeable difference. I'm not looking to apportion blame here, just trying to find a solution. Have also noticed the problem with other makes, though not as much as Hornby. Seems to me the body acts as a magnifier, a sort of 'megaphone' effect. Anyone else have any thoughts on the matter, or more importantly, can anyone suggest a solution. A 'paint-on' liquid rubber perhaps?
***Most of the answers are spot on: The issue is "sympathetic resonance" and the body is acting like a speaker and vibrating at a frequency created by the mechanism. The adding of mass is often the answer, as "soft" fillings are actually only useful at high frequencies, and then only when a LOT of the material is used, and this isn't practical when talking about a tank loco.
Mastic and the like are good solutions, but messy. I'd suggest that plastiscene or blu-tack will do a lot, with extreme cases fixed by adding small bits of lead sheet randomly to the cavity (tank) walls as the best answer. (use a flexible type glue).
Neat work doesn't always rule here.... Random "stressing" of any surface will usually stop it resonating better than neat symmetrical additions.
This effect is usually worse when there is a clipped on (as in tender body) or body fixed very firmly to the chassis by two screws / one front and rear. It can be made better by having one screw plus a lip or similar holding the body, with the area round the "lip" having a pad of foam tape or similar as a "damper"