Greg writes:
> While I haven't had experience with remote machinework, I can answer #4.
> The reason that the English Spit 1500's use a double valve spring setup
> is so that the engine can rev higher.
(Greg goes on to explain how double springs help to prevent valve float,
apparently by increasing the spring rate).
But Greg, wouldn't a single, stiffer spring increase the spring rate more
cheaply? (yes...) Actually the double spring does two things to help with
valve float - it increases the spring rate, and it helps to avoid harmonic
oscillations. Any given spring with a mass attached (like a valve spring)
will have a natural frequency at which it will oscillate, and a number of
other harmonics of that frequency at which oscillation will occur. Such
oscillation is not conducive to proper functioning of the valves - if excited
at the natural frequency, the valve would start flapping up and down with
little reference to the cam lobe. Using two springs with carefully chosen
dissimilar spring rates makes it so that at least one of the springs is
still pushing up on the retaining cap at any given frequency, even if the
other one is at its natural harmonic.
> Since the opening and closing of the valves needs
> to be precisely timed, valve float reduces the efficiency of an engine.
Not to mention the amount of damage that occurs when the valve slams
back into contact with either the cam lobe or that vlave seat, whichever
comes first...
--
---
John R. Lupien
lupienj@wal.hp.com
|