Question: Dwell vs. Points Gap

[lespaul]

If the dwell is set properly, does that mean the points gap is correct as well?

[bkreigsr]

yes.
but usually you would set the points gap after a dizzy removal, points replacement, or such, then set it to spec using a dwell meter.
the dwell meter shows the angle (gap) that you just set.
Bill K

[Bill Verburg]

The bigger the dwell angle the smaller the point gap and vice versa

it's best to set them up at the wide end of the gap(low end of the dwell spec)

[lespaul]

Thanks.

[Peter Zimmermann]

Dwell: The amount of degrees that the ignition distributor turns from the place at which the points close, until the place that they open for the next cylinder. Good advice above, if your dwell spec is 38 +/- 3 degrees, the best place to set the point dwell would be 35 - 37 degrees. The beauty of using dwell is that you don't have to mess with "gap," just eyeball them until they open with the rubbing block on a cam lobe, start the car and use the dwell meter to make further adjustments.

[Paulporsche]

I agree w/ Bill. If you set it w/ a wide gap(low angle number, say 35) as the rub block wears down, the gap will narrow and the dwell angle will rise, eventually getting to 41, when it's time to change the points.

[cmcfaul]

Good luck, the + /- 3 is about a zillameter (very, very small adjustment). expect some trial and error before getting it just right. When perfect, the car will run great for a while. Highly recommend replacing the points with a Petronics or other breakerless ignition.

Chris

73 911 E

[Bill Verburg]

Originally Posted by mcfaul

Good luck, the + /- 3 is about a kilometer (very, very small adjustment). expect some trial and error before getting it just right. When perfect, the car will run great for a while. Highly recommend replacing the points with a Petronics or other breakerless ignition.

Chris

73 911 E

I always pulled the distributor and set the points on a bench, very easy to get as much accuracy as possible, much easier on the back too

[T77911S]

how critical is the dwell? say it was set at 30 or 45 deg. what would be symptoms of this?
the points only provide a ground to the CD unit, there is no voltage on them to create the spark. if the gap was too wide would it reduce the charging time of the CD thus affecting high rpm running?

[bkreigsr]

my 73 MFI would only run best when dwell was 38 deg exactly.
Symptoms that I was not there were: tach bounce, high speed miss/no power, rough idle, to the point of stalling, and hard starting.
73.5 with CIS might not be as sensitive.
Bill K

[Peter Zimmermann]

Originally Posted by T77911S

how critical is the dwell? say it was set at 30 or 45 deg. what would be symptoms of this?
the points only provide a ground to the CD unit, there is no voltage on them to create the spark. if the gap was too wide would it reduce the charging time of the CD thus affecting high rpm running?

One must always assume that a tuner/technician will set the dwell within the allowable range calculated by the factory. At that point the ignition timing must also be set, because one degree of dwell is equal to one degree of timing. As the points wear (close up) from their correctly installed setting, the dwell, and timing, will change, creating a retarded condition that will also cause backfiring, maybe tach needle bounce, and generally sluggish running (more easily recognizable when the dwell reaches 43-44 degrees). If, at install, the points are set too wide (smaller dwell number), let's say 30 degrees, if the timing is reset to factory spec at that dwell there will be little evidence that something might be wrong.

[RWebb]

BIngo - hence one benefit of breakerless ignition -- it doesn't change. And once they got some reliable semi-cond. devices in there (late '70s?) they work as long as you do...

[Peter Zimmermann]

Originally Posted by RWebb

BIngo - hence one benefit of breakerless ignition -- it doesn't change. And once they got some reliable semi-cond. devices in there (late '70s?) they work as long as you do...

Bosch ignition points became so unreliable at some point in the '80s, due to pronounced rubbing block wear, that my shop installed many, many breakerless ignition kits into 911s, even a few 912s, and ended the issue once and for all.

[bkreigsr]

then again, there are those of us who enjoy setting the dwell every thousand miles or so.
one of the few things where the reward is about twice the size as the effort.
Bill K

[Paulporsche]

Peter and others,

Just a hypothetical here. Say we call the service life of the points 12,000 mi. Why not set the timing correctly @ 35 degrees when new, then @ 38 degrees reset timing to the original spec. Then @ 41 degrees replace.

BillK,

How long can you go w/ your procedure? Can you keep the dwell @ 38 until the block wears down completely? Is there that much room to maneuver in the points themselves?


Everyone,

Or would it be best to reset timing every so often and let the points wear down naturally? I have read on other posts here that w/ the CDI system, the dewll change does not affect the timing, as it does in conventional systems? Anyone know for sure?

[bkreigsr]

Paul, there's an inherent flaw in your hypothetical reasoning. As the block wears down, the gap (dwell) also changes. There would be no point to setting to 35,38,41 as the block changes, as the values should always be to factory spec.

and yes, I could keep the dwell at 38 deg until the block wears down, but in reality, by that time, the points probably are beyond their optimal service life. Besides for less than $10, why not replace every couple thousand miles?

Bill K

[Bill Verburg]

the rubbing block wears(it helps to use a dab of the supplied lube) w/ use, that's why you set them up at the low end of dwell(wide gap) so it stays in spec longer, as the gap decreases it causes a slight retardation of static spark timing because the points open slightly later as wear occurs.

[Flieger]

I am trying to wrap my head around all of the great information here.

Can someone please post a photo of the distributor internals setup in the car?

[Paulporsche]

I think what I'm saying is the same as Bill V. This is how I've always done it. Let the timing vary slightly as the points go through their swing from 35 to 41.

Bill K, what I'm saying in my first scenario is not to reset the dwell to 35 38 or 41, but reset the TIMING as the dwell goes through its range. That would seem to me to keep it closer to correct timing.

In my second scenario, why not reset the dwell from time to time, so the timing never goes too far astray. I realize that by the time 38 is no longer able to be maintained, they are probably pitted beyond use.

It seems that either of these techniques is better than what I've always done.

Of course all this is moot if , as someone pointed out once in another thread, the timing does not change along w/ the dwell in CDI cars. Can anyone confirm this? Has anyone ever checked to see if their timing changed under these circumstances?

[Porsche-O-Phile]

Subscribing.

This is great information. For one, I'm still trying to learn/understand the nuances of points ignition (I have points/CDS on my '74).