Setting the points on 69 Marelli dist? what is the setting?

[Erik Mckenna]

Thanks guys!

[Bill Verburg]

Marelli points gap = 0.016"(0.4mm)

[Jbabic]

Yea, what he said. Erik, once I find all my old literature on 3.0 Liters..your more than welcome...tech booklets and such.

[dweymer]

Related question for all: isn't the dwell more important than the gap. If you set the gap to spec and the dwell is out of spec; which is more important? I never understood this fully..

[911pcars]

Dwell is related to point gap.

Dwell is how long the points remain closed as measured between the angle between the distributor cam lobes (6 lobes, 1 for each cylinder).

360º/6 = 60º, the maximum dwell time for each cylinder, which also translates into the points remaining closed.

It's been awhile, but I think 30º dwell should be equivalent to about 0.016" point gap. Others can correct me.

Increase dwell time = point gap decreases
Decrease dwell time = point gap increases

In a pinch, a match book cover (seen one around lately?) or a business card is around 0.016".

Hope this helps,
Sherwood

[Erik Mckenna]

Thanks GUYS!!!!

[Bill Verburg]

Dwell and point gap are 2 different ways of measuring the same thing, dwell is usually more accurate.

Points are just a high speed switch, operated by the distributor cam high points, when closed they allow current to flow into the primary circuit of the coil, when open current flow to the coil stops, collapsing the magnetic field in the coil primary, inducing high voltage in the secondary coil winding which goes to ground through the sparkplug gap in the combustion chamber.

what you want is for the points to be open for x&deg of crank rotation just before ignition is to occur, this saturates the coil.

for a Marelli dwell should be 37&deg &#177 3&deg

shorter dwell is the same as a larger gap, longer dwell is the opposite.

[911pcars]

"what you want is for the points to be open for x° of crank rotation just before ignition is to occur, this saturates the coil."

"Open" is probably a typo. The points are closed during coil saturation. The larger the dwell angle, the longer the magnetic field builds up in the coil for more potential secondary voltage.

Sherwood