I happen to agree with Ed. An engine vibrates a lot and each of those
vibration pulses flexes a rigid connection. After time you get flexural
cracking of members. And if the members and joints are painted, you are
not likely to see of find them until someting breaks. I am a big fan of
giving joinst between differet components some compliance or forgiveness
to such vibrations. I use the sidewall of an old tire cut in donut
shapes with a hole in the middle to isolate engine and tranny vibrations
from my frame. They are about 3/8 inch thing, are pretty stiff but give
a large degree of isolation. Remember structural flexing breaks things.
mayf, out in Pahrump with the first cuppa and my eyes still closed mostly
Ed Weldon wrote:
>OK--everybody get your tomatoes ready to throw--- engineering stuff incoming:
>I'd be inclined to be a little careful about rigid mounts unless you have some
>experience and know what you're doing. You don't want to overconstrain things
>and end up distorting something that shouldn't be or worse yet putting an
>unnecessary load on a bearing somewhere in the drive train. You need to deal
>with things like thermal expansion, chassis flex and just plain realistic
>levels of accuracy in building the car. A three point rubber mount for an
>engine/trans takes care of a lot of this as does your driveshaft universals.
>The vibration isolation of the rubber comes as a bonus.
>There's an old concept in mechanical engineering getting some new play under
>the name "Minimum Constraint Design" A Google search on this subject will
>bring up a good engineering book on the subject and some lofty discussions.
>It's probably more for engineering types than us racer-builders. Still, if
>you're into something pretty ambitious like a +300 mph car with the attendant
>innovative design that inevitably happens it wouldn't hurt to have a good
>understanding of this subject.
> Bottom line is that a 4 legged chair won't sit right on the floor unless all
>four legs are the same length AND THE FLOOR STAYS FLAT.
>Ed Weldon
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