Pat,
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. Since the camshaft lobe only pushes
the valve open, it is the responsibility of the valve spring to close the
valve. It is also the valve spring's job to do this fast enough to keep the
cam follower in contact with the backside of the camshaft lobe while the
camshaft is turning.
The faster you run an engine, the faster the camshaft lobe rises and pulls away
from the raised cam follower, and the faster the valve springs have to react to
ensure the follower remains against the camshaft lobe. "Float" occurs when
the camshaft lobe and follower don't make contact as the lobe turns its
backside to the follower. Since the opening and closing of the valves needs
to be precisely timed, valve float reduces the efficiency of an engine.
Double valve springs effectively raise the rpm at which 'float' occurs.
Ignition breaker points also experience float, and this is one argument
for using an optical trigger or reluctor-type ignition trigger.
I believe that Ducati motorcycles have a system that pushes the valves open
and then pulls them closed, mechanically.
As for machine work, I like to talk with the machinist and have him go over
any specific problems that were encountered during machining, or areas of the
piece that might cause trouble during assembly.
I hope this helps your project.
Greg Meboe MEBOE@wsuvm1.csc.wsu.edu
Dept. of Mechanical and Materials Engineering
Washington State University
'67 Spit-6 (daily) '74 TR-6 (project)
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