Dwell importance..

How does dwell on the points affect timingl?

Is it true the dwell being off 1 degree affects the timing 5 degree?

Gapping the points to the "matchbook" can't be right on all circumstances, and the effect on the timing must be greater than the apparent simplicity that it implies...

 

Re: Dwell imprtance..

The main point is - set the dwell before you set the timing. Approximate dwell (match cover, feeler gauge, etc) won't affect the timing if you set the dwell before you set the timing.

The dwell is specified to give the optimal fraction of time (the dwell angle in the rotation of the distributor) devoted to charging, and then discharging, the coil. You can set the charge/discharge approximately (match cover, feeler guage, etc) and then set the timing, and the engine will still run fine.

Since the distributor rotates at half the speed of the crankshaft, I would say that a change in 1 degree of dwell translates to 2 degrees of timing.

 

If given the gap and dwell and you have a dwell meter ignore the point gap and set for the dwell angle, its always more accurate.
Steve is right though it always did seem kinda funny that they did not design all distributors to be set while the engine was running instead of benching it.

Here is a handy tool for anyone that still runs points.

It is a Tungsten point file for cleaning the points.
They work great for tons of stuff, we use them at work for intricate filing on small inserts.

 

Only because you ask

Dwell angle is a measure of the duration of time that the primary circuit of the ignition system is closed to energize the primary windings of the coil. It expressed (and measured) in degrees of rotation of the distributor rotor, hence the use of the term "angle".

In actual operation, as the distributor mechanism rotates, the points (or electronic module in electronic ignition systems) are closed for a certain number of degrees of rotation, and open between these points. Simply as a matter of interest, this means that the total number of degrees during which the points are closed, plus the total number of degrees that they are open, will equal 360 degrees.

In four cylinder engines, there is usually ample time for the primary circuit to be open and closed (to energize the coil) four times during each revolution of the distributor, which makes the dwell value less critical than in 6 and 8 cylinder engines. In four cylinder engines, there is more of a concern over having too much dwell time (during which time the coil is energized) which can result in high coil temperature and premature failure.

 

You have a link for that file Mike? I went to the Simonds site and could not find it.

 

I forgot to add how dwell effects timing:

The dwell is adjusted by setting the points gap to a specified distance at maximum opening. A narrower gap gives more dwell and a wider gap gives less. Taking it to extremes, excessive dwell means that the points close too soon after opening, cutting off the magnetic field collapse before it delivers all its energy. Too little dwell gives the magnetic flux insufficient time to build up to the maximum.

Both conditions give a weak spark which gets even weaker as the engine RPM rises and produces misfiring at normal operating speeds. The dwell, as well as spark plug gap, do have an effect on ignition timing. The later the points open, the later the spark comes and retards the timing. The earlier the points open the sooner the spark comes and advances the timing. That is why timing is the last thing to be set in a tune-up

 

Tim, I don't use a Simonds, that was the only good picture I could find. We have a Nicholson plant right down the road and every year or so they have a yard sale so to speak. We bought about 15 of them for work.
The look just like the picture, you can get them from mscdirect.com
Here is a link:
http://www1.mscdirect.com/CGI/NNSRIT?PMPXNO=2290443&PMT4NO=51213914

They are $4.92 a piece, MSC #: 90795550

The Nicholson is better then the Simonds as they are double cut instead of single cut, the Simonds is also available from MSC and is about .90 cents cheaper. MSC #: 98488067

They are handy for gun work and all kinds of things that are small.

Hope this helps!!

 

I don't know what the big prob is with not being able to have the engine running when setting dwell.
I set it using the remote starter button thingy with the dizzy cap off.
I haven't seen more than a 2-3° difference with that setting than with it running :?

 

Can anyone go through the procedure of setting the dwell with a dwell meter and a hot wire(battery to starter wire).

Thanks

 

Here is one way that works and I,m sure there are many more options.

The way I set the dwell is this; remove the distributor cap and rotor, ground the coil wire and remove all the spark plugs from the engine. Set up your dwell meter and hook up a remote starter. Turn the key ON and crank the engine. Adjust the points to the desired setting and tighten the points. Crank it again to be sure the dwell angle is still correct.

 

Yep, just the way I do it ... except I'm too lazy to pull the plugs.

Hot wire: use the solenoid ... wire from tiny lug to big pos lug on solenoid. Remote starter button much handier.

 

Another way is to set the points gap and start the engine. Check the dwell angle. If it is a bit high, shut her down and open the points slightly, if a bit low, close slightly. Personally, I have never found any real difference in how an engine runs when looking at + or - a degree. Just remember as stated before to reset the timing when your done.