Setting point gap on pony motor

[chas036]

I just installed a rebuilt distributor on my 720D , new coils, points, etc. I set the "V" timing mark on the fly wheel to match the "V" on the housing. When I went back to look at the points to set the point gap, I noticed that both sets were open. Is this the way it is suppose to be? Two cylinders firing at the same time?

 

[chas036]

How does this distributor work anyway? I see two coils each with two plug wires exiting. I see one set of points for each coil. When one of the points open, how does the coil know which plug to fire?

 

[Bob]

Sounds normal to me, and for it NOT to be normal, someone would has had to alter the distributor "cam".

Take note of the exact engine rotational position the points "break" (just open enough to end electrical continuity)... that is the exact time each spark occurs.

I believe you will find each set of points "breaks" at a different crankshaft position.

 

[Bob]

The "pony" uses a "waste spark" ignition system like some newer cars... each coil sparks two cylinders at the same time... one is near TDC on the compression stroke, ready to fire, the other paired cylinder is coming up on TDC of the exhaust stroke, and that plug sparks as well, but is harmlessly "wasted".

One turn of the engine later the situation will have reversed... the cylinder that needed to fire last revolution will be near the end of it's exhaust stroke, and the cylinder where the spark was "wasted" is now ready to fire.

Of course, 180º crankshaft degrees in between, the other coil is firing the other two cylinders in the same manner.

 

[chas036]

When I set the flywheel "V" mark to match the housing "V" mark, and I have the distributor housing at the middle point of its adjustment travel, I then see both set of points open. Is this the correct location to have the distributor to set both points to .020, and should I see both open? If I under stand it correctly, all four plugs will see spark at the same time because if I set both points to .020 gap at this position of the cam, both sets of points will fire at the same time.

 

[Bob]

You are overthinking this.

IGNORE the timing marks while setting the points, set the points one set at a time to .020" when they are at their most fully open point.

One the points are set, THEN set the timing

The points are mounted 90º apart, so the "breaking" events occur 90 CAMSHAFT degrees (180 CRANKSHAFT degrees) apart.

There is only ONE spark, at the instant the points "break", so just because they remain open at the same time doesn't mean all sparks occur at the same time!

It is a 4-cycle engine, so each and every cylinder fires during two turns of the crankshaft, then the cycle repeats.