At 07:39 AM 5/3/2007 -0400, Paul Osborne wrote:
>.... Looking for input on the advantages/better choice of single or
>double valve springs on a 18v head. ....
Lighter valve springs cause less wear on the entire valve train,
especially cam and tappets. For purpose of longevity, it is
desireable to use the lightest springs that will get the job
done. The change from double springs to single springs with the 18V
engine was accompanied by a change from tall heavy tappets to short
light tappets and longer pushrods. The lighter tappets can be
returned with less spring force at high speed, and you have a longer
wearing engine. They changed from double row to single row timing
chain and sprockets at the same time (as a cost reduction), as less
power is required to run the camshaft with single valve springs and
lighter tappets.
A high lift camshaft imparts more motion to the valve train,
therefore inducing more inertia to the moving parts and requiring
more spring force to return the patrts at high speed. A high
performance engine expected to run at higher than normal speed would
need stronger valve springs. Inertia can be reduced by using lighter
parts in the valve train, such as the short tappets or alloy spring
caps. It is a functional trade-off. Heavier parts and higher speed
needs srtonger springs and causes faster wear. Lighter parts and
lower speed allow use of lighter springs and reduce wear.
The 18V engine already has the right combination of parts from the
factory for successful use of single valve sptrings. Since
installing double springs can increase the wear rate, the only reason
to do so is if you are upgrading performance specs of the engine for
higher valve lift or higher engine speed. If you do install double
valve springs in your 18V engine you should also install the double
row timing chain and sprockets,
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