Exactly--points are actually fairly complicated and involve a lot of design
tradeoffs. If the spring is too stiff the rubbing block wears. If the ramp
is too steep the inertia overcomes the weak spring and tosses the points
open, causing indeterminate dwell (you can see point float on a dwell
meter). With dual points, one set of points is essentially controlling the
opening, and the other the closing, so point float doesn't matter. The
closing point opens first, but the opening point is still closed, so current
keeps flowing to the coil. Then the opening point opens and the current cuts
off, yielding the spark. By the time the opening point opens, the closing
point is all done floating and is back on the ramp, which now closes the
closing points. Presto. Cool, eh.
Bill Babcock
Babcock & Jenkins
-----Original Message-----
From: owner-fot@autox.team.net [mailto:owner-fot@autox.team.net] On Behalf
Of Randall Young
Sent: Thursday, June 16, 2005 11:29 AM
To: triumphs@consolidated.net; fot@autox.team.net
Subject: RE: Mallory Unilite Distributor
> Now that I have converted to negative ground, I am using a MSD box.
> The points have lasted for years (I have never changed them).
FWIW, I had the same experience with a Lucas dizzy & a MSD. Same set of
points worked fine for 15 years, and were still working fine when I
converted to an optical pickup (because of excess wear in the dizzy).
> Another elementary question: What is the purpose of two sets of points
> in a distributor?
They are phased slightly differently (one set opens first), which allows for
a longer dwell time without having a faster ramp (which can lead to point
bounce).
Randall
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