But wait! There's more!
Dual springs also allow the designer/engineer to set the resonant
frequency of each spring to a different value, and to get some damping
into the system so that it can operate closer to the resonant
frequency. The springs operate close to each other such that the
inner spring's OD clears outer spring's ID by a small amount.
Friction between inner and outer coils damps the resonance.
And all the rest that Carter mentioned is true, too.
Donald.
> Date: Sat, 11 Nov 2000 17:48:35 -0800 (PST)
> From: Carter Shore <clshore@yahoo.com>
>
>
> Main advantages of dual springs:
>
> 1) Allow greater valve lift by reducing the bind
> height of the coils (two skinnier springs can be
> compressed more than one fat spring)
> 2) Allow higher overall spring rate, to raise the RPM
> where valve float occurs. (sum of the pressure from 2
> skinny springs can be greater than the pressure from
> one fat one)
> 3) Allow longer spring life, by reducing the torsional
> loading on the spring material.
>
> Skinny and fat refer to the thickness of the wire that
> the springs are wound from.
>
> Unless you are running a higher than stock lift
> camshaft, higher ratio rocker arms, reving above 7,000
> RPM, or powering an aircraft, then dual springs will
> be of little benefit.
>
> BTW, the valve seats need not suffer. It depends on
> the spring rate and the installed height of the
> package (springs, retainers, shims) used. Static
> closed seat pressure does not have to be any higher
> with duals than singles. The machine shop should check
> this, it really is important.
>
> But they *do* look cool!
>
> Carter Shore
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