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
--- SJagGo@aol.com wrote:
>
> Hi Dave,
> DO NOT use double valve springs with your current
> spring seats. When I
> rebuilt my first Spitfire engine many moons ago, the
> machine shop I had do my
> head ordered new valve springs. They came with an
> inner set, so he put them
> in. In a matter of a 1000 miles or so they will
> chew up the normal valve
> seat leaving all kinds metal everywhere in the
> engine. Now I order all parts
> myself. I'll still have a machinist install the
> valve seats, but valve
> guides are easy to install. Lapping the valves
> isn't difficult but they
> don't charge very much for it. What they can also
> do, is magnaflux the head
> to find any cracks that aren't readily apparent.
> Have this done before you
> waste your time and money on parts and labor.
> Bill Brockschmidt
> 7 spits
> 64 OTS Jag
> 65 S-type Jag
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