[Healeys] dwell

[richard.ewald at gmail.com (Richard Ewald)]

Dwell is a measurement of the angle between when the points close and when
they open again.
Roughly speaking the points are going to be open about 120 degrees out of the
360 degrees in a full circle. That leave 240 degrees (approx) of closed time
divided by the number of cam lobes. So take a 4 cylinder engine has 4 lobes on
the dist cam we have 240/4= 60 degrees of dwell. Depending on engine design
the range for these engines is 58-62 typically.
A 6 cylinder engine gives us 240/6= 40 with a typical range of 38-44 degrees.
A V8 has twice the lobes of a 4 cylinder so you have 30 degrees with a range
of about 28-32 degrees.
Analog dwell meters typically have two scales a 6 cylinder scale and an 8
cylinder scale with a note to double the readings if you have a four cylinder.
So if someone with a six cylinder engine says they have the dwell set at 30
degrees either they are reading the 8 cylinder scale or their points are WAY
WAY off.
Anyone who works with distributors who doesn't realize that 30 degrees is the
wrong scale for a six cylinder in .001 seconds is an idiot IMHO.
BTW a couple of notes about dwell. Set points to the minimum end of the spec
range. As the rubbing block wears the points will be closed more and the dwell
will rise. By setting to min you ensure they stay in the proper range.
After you have them set correctly rev the engine and watch the dwell it should
not change by more than a degree or so. If the bushings in the distributor are
bad the dwell will jump all over the place.
Rick

Sent from my iPhone

On May 13, 2012, at 6:37, "Alan Grossman" <agrossman at pacific.net> wrote:

> I don't understand either of these statements.