Dan,
Kudos for one of the most precise, complete explanations of dwell angle that I
have
come across. Being a charter member of the OF club, I learned about the
relationship
between dwell angle and point gap a long time ago, and have never forgotten it.
It's
really quite simple, but, as pointed out in an earlier post, with the
diminished use
of point-type ignitions, younger folks are often mystified.
I would add my support to those who champion the use of a dwell meter for
setting
point gap. Now if we could come up with some way to use a meter for setting
valve
clearances.......
No one has mentioned the relationship of point gap/dwell angle to timing. Just
as a
reminder to always set the point gap first in the tuneup process, remember that
as the
point gap widens, your timing will become more advanced (the points open sooner
in the
cycle.) Likewise, when the gap decreases, timing retards.
--
*Bill Schooler *Check the MGCC Wash DC Centre Web Page
*Woodbridge, VA *http://members.aol.com/mgccwdcc/
*schooler@erols.com *Editor of The Spark
*69 B/GT, 53 TD *Web Page Coordinator
DANMAS@aol.com wrote:
>
> In a message dated 97-05-30 19:20:47 EDT, randyr@starwave.com (Randy Rees)
> writes:
>
> > I never could figure out how you could set dwell and gap with only one
> > set screw.
>
> Randy:
>
> As a matter of fact, dwell and gap are two ways of saying the same thing.
> Actually, the gap setting is derived from the required dwell angle. Dwell is
> determined as follows:
>
> For each complete combustion cycle, ie. two revolutions of the crank, the
> distributer rotor makes one revolution, or 360 degrees. For a four cylnder
> engine, each cylinder has a maximum of 90 deg distributer rotation (360/4).
> During this 90 degrees, the points must remain closed long enough to allow
> the magnetic field to build up in the primary side of the coil, and then open
> to allow the field to collapse, generating a high voltage discharge from the
> secondary side. If the points don't stay closed long enough to build the
> magnetic field, a weak spark will result. Too long, and the discharge time is
> reduced. This is a particular problem at high RPM. For a 6 cylinder engine,
> the maximum rotation for each cylinder is 60 degrees, and for an 8 cylinder,
> 45 degrees. Typically, the ratio of closed to open is on the order of 3 to 1,
> ie closed 60 degrees, open 30, for a 4 cylinder.
>
> Adjusting the timing sets the crankshaft angle (based on piston position in
> the bore) at which the points open, and adjusting the point gap determines
> how long they stay open, thus setting the dwell angle. A smaller gap
> increases the time the points are closed, and a larger gap the opposite.
>
> Hope this helps!
>
> Dan Masters,
> Alcoa, TN
>
> '71 TR6---------3000mile/year driver, fully restored
> '71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
> www.sky.net/~boballen/mg/Masters/
> '74 MGBGT---3000mile/year driver, original condition
> '68 MGBGT---organ donor for the '74
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