Dwell angle

The original owner burned up the engine at 18,000 miles, so she had installed one from a '69 Comet. Now I have some electrical parts using 1969 specs and other from 1970. My Motors Manual says distributor gap is 0.17 and 0.21 respectively. What component determines this difference and how does a change affect engine performance?

Wow! I haven’t had to adjust a dwell angle in over 15 years, not since my son gave up on the Fiat roadster I restored for him.

The gap is the distance between points and is easily adjusted using a set of feeler gauges and a screwdriver. To measure the dwell you need an inexpensive instrument called a dwell meter. Check online for sources. To adjust the dwell, try this reference: http://www.moyermarine.com/faq/4.5.html. You probably will also need a timing light. These items come with instructions.

Wow. It’s been years.
As to how the dwell angle affects performance…

The function of the points is to control the spark. When the points are closed, current runs through the coil. When the points open, the current stops and the magnetic field that it was generating collapses into the coil’s core and induces a voltage spike. If the points are not closed long enough the field will not be strong enough and the spark will be weak. If the points are not open long enough the collapse of the coil’s magnestic field will be incomplete and the spark will suffer. The “dwell angle” is a measurement of how many degrees of distributor shaft rotation the points are closed for (or is it “open for”…it’s been soooo many years!). That tells you whether the points are open and closed for the proper amount of times.

Don’t forget to lube the distributor shaft cam!

Try and find a mechanic under 30 who’s actually seen points.

try a boat engine

there evry where!

This Auto Zone Website says 24 to 29 degrees: http://www.autozone.com/N,23299999/shopping/specsSelect.htm Click on this to get more useful information.

You had it right, it’s a measure of how long the points are closed. The dwell needs to match the coil. Too little time and the coil will not be fully charged. Too long and some of the charge will bleed off.

Never thought of that…but then again…MOST mechanics don’t work on boats.

If the gap is between those two figures, then you don’t have to change it. Anything between those is fine. If the gap is .016, you loosen the screws and widen the gap. This is done with the points fully open. At the highest point of the distributor cam.