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MG MGA - Dwell -- how fussy?

I'm getting 66-68 dwell reading (doubling the V8 scale). Is this close enough or should I be spot-on 60? Thanks.

Jim
58 MGA
J Plegue

Jim,
The dwell is the amount of degrees that the points are closed, and affects the primary voltage, affecting the heat buildup of the coil. If the dwell is too long, it can lead to a shortened coil life. Having said that, I know of nobody who has really ever had a coil fail, so take that for what it is worth. I don't think that a 66 degree angle will give you problems. If you get the dwell angle set correctly, you don't have to worry about the point gap, as that is how you set it. So, if you want to be accurate, set the dwell. If you don't think it matters, set the points, and if it runs fine, leave it alone.
Mike Parker

Thanks. I went back and messed with it some more, got it down a few more degrees, around 64-65.I think I'll leave it at that.
J Plegue

Jim. I would open the points a little more. As noted, the dwell is the period the points are closed and charging the coil. The remainder of the period, some 30 degrees in this case, is the amount of time the charge builds in the secondary windings of the coil and the spark is induced in the plug. As the points wear, the dwell becomes larger (longer) and we begin to see mis-fires at higher engine rpms due to this. Set the dwell correctly and the engine should run better for a longer period of time.

Les
Les Bengtson

I'll take another shot at it. Is dwell a more precise indicator of the proper setting than the actual gap when measured by a feeler gauge? Right now I've got it set at .016 to get 064-065 dwell. I'll go up to .017 and see what happens with the dwell. Thanks.
J Plegue

Jim, I used to accurately set the dwell on the old Saab V-4's I used to run in the following way:


Connect a remote starter switch (alligator clips on the ends) to the starter or have an assistant in the car. Leave the point adjusting screw snug but loose enough to make an adjustment. Connect a dwell meter. Spin the engine while watching the dwell meter and adjust the points as necesaary. Tighten the adjusting nut, spin the engine again to confirm the setting.

Al T.



A. Tirella

Another point to consider is that changing the gap/dwell also changes the ignition timing. If you change it from where it was when the timing was set, the timing will change. As the rubbing block wears, and the dwell increases, the timing is also being retarded.

Jeff Schultz

Well I have had my coil fail. Can't say that it was due to the dwel being set poorly though. The dwell is the electrical measurement of the point gap. Nothing more or less. With use, there will be metal migration from one contact to the other. This usually will make the setting of the points difficult using a feeler gauge. If set mechanically, the electrical dwell will be less than optimal. Either way is acceptable if the points are in good shape.

I see nothing wrong with 64-65 degrees. It should work just fine. Al's method will work fine for setting dwell.

As already stated, the timing should be reset after adjusting the points.

Chuck
Chuck Schaefer

The normal spec for setting dwell is plus or minus 1° when installing new points and plus or minus 3° when checking them during their lifetime. I always set the points in our cars on the minus side because, as Les stated the dwell tends to get longer over thelife of the points due to wear on the rubbing block. that is just my own preferance and 4° to 5° should be fine, but will require resetting the points sooner than if they were closer to start with. Also, if you are using a dwell meter, don't bother with the feeler gauge or conversly, if you are using a feeler gauge, don't bother withthe dwell meter, they are just two different means of doing the same job. Cheers - Dave
David DuBois

I agree with the other posts but will add my 2Ps worth as to why its important to run the correct dwell and therefore gap. If the dwell is larger the points gap is less. Add to this that the points will close usually another 2 thou fairly quickly with bed in. The gap breaks the current, if too small a gap the current is not broken with a crack (more a fizz)as the current tries to jump the reduced gap. The gap is also the cooling period for the points and if insufficient will shorten the life of the points.
DENIS H

Dwell is a measurement that is taken running and as such takes into account any wear in the system. Point gap is an APPROXIMATE way of getting dwell. Dwell is accurate, Point gap is a guess.
Always set the dwell at the minimum spec to start as wear makes the dwell # go up. Set to 60 and when it gets to 65 reset to 60. As dwell/gap changes it changes the ignition timming so always set timming after setting dwell/gap. If you chose to set by gap set to max spec of .016 to start. As points wear the gap gets smaller.
R J Brown

This thread was discussed between 10/06/2007 and 11/06/2007

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