Ask the Mechanic

What's the Point: Point Gap and Condenser Electrical System

(Getty Images; Photo Illustration by Barry Falkner)

READER: I have a couple of questions about the conventional points and condenser electrical system on my Ford 850 tractor. The first question deals with the points. Does the gap on the points affect engine timing, and when does the spark happen at the spark plug -- when the points break open or when the points touch when they close? Also, what is the purpose of the condenser?

STEVE: When the point gap is lessened, the timing is advanced. Point gap varies with different engines. Changing the point gap is similar to rotating the distributor. The gap on the spark plugs needs to be within specs, as that can also change engine timing. As the lobe on the cam in the center of the distributor that opens and closes the points rotates, the closer the point setting, the sooner the points are opened by the "heel" of the points. As the points break, the charged primary winding in the coil supercharges the secondary winding in the coil, which is looking for a ground (like all electricity), and the spark plug ends up being a good ground.

That is why a spark plug will not spark if you hold it up in the air. But, if the plug wire is bad or you touch the spark plug, then you know what happens when you become the ground.

The condenser is actually a capacitor that stores volts and adds additional volts to the coil's output. It also helps absorb some of the voltage to help from damaging the points.


-- Write Steve Thompson at Ask The Mechanic, 2204 Lakeshore Dr., Suite 415, Birmingham, AL 35209, or email, and be sure to include your phone number.