What the Dwell ?

[malloyjp]

I recently put new points in my distributor and set the gap to what I thought was the correct gap, but the dwell meter is reading low. It's reading 24 , and the correct dwell is supposed to be 29 per the manual. The car is running good though. I'm confused because the points that I replaced were really shot, but the dwell meter was reading spot on at 29 with the bad points.

How can I get the dwell setting correct ? I know a low reading indicates the gap should be less , but I'm not sure how to adjust because the gap seemed correct .

It's a 69 mustang mach1 with 351 windsor and original autolite distributor. Thanks !

[Daves55Sedan]

Its impossible to find a dwellmeter nowadays, so I just use the feeler guage to gap the points and forget about it. It runs good enough for me like that. But in the old days when I did have a dwellmeter for 6 volt system, if the dwell angle was off, you can loosen the screws that hold the point set down to the breaker plate but leave enough friction that they will still be snug yet moveable with a screwdriver. Jus tweek the position slightly, re-tighten screws and check your dwell angle again. A couple of trys and you will have it spot on.

[George49Ford]

I agree with Dave. My Dad worked on many engines all his life and never owned a dwell meter or a feeler gauge. Just set the points by "eye balling" and sound of the engine running good or not and always seemed to have good running car. My eyes and ears were never that good so I always had to use feeler gauge and dwell meter.

[LOWRIDER]

If you have a dwell meter snug the point screws like Dave mentioned then disconnect the vacuum advance line. Next have a friend crank over the engine and adjust the points to the 29 degrees while it's cranking. Tighten the screws down & recheck the dwell to make sure it hasn't changed. That's the way we did Fords back then. GM cars had the window on the side of the cap & you could adjust them while it was running.

[billwill]

a match book will doit.goodluck

[craig]

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24 degrees is close enough, in time you will end up at 29 as the rubbing block wears, the points close up and the dwell increases. 1969 was about the time Ford started using a different breaker plate, a lousy design that wears out after time. What happens when it wears is that the dwell is not consistant because the pivotal points wear and when the vac advance moves the plate, the dwell increases(closing the points) even more. If you can move the breaker plate side to side by grabbing the points, then you need a new plate

[Motorhead6]

Dwell is the more precise way to gap the points(you obviously have access to a dwell meter or you wouldn't be asking the question). I believe, however, dwell is the amount of rotation that the points are open and that more dwell requires more gap. Try and see, but my experience is such. It usually takes about .018" or .019" of gap vice the .016" the spec sheet calls for. In any case, the dwell reading is what you should go by. Over time, the gap will possibly close up a bit and the dwell will also change. Keep in mind too that the ignition timing will change one degree for each degree of change in the dwell reading so re-check the timing as you alter the dwell reading.

[55Brodie]

Actually, dwell is the angle measurement in degrees of camshaft rotation that the contact points remain closed. A larger dwell angle equals less gap and allows the coil to fully saturate.

[Motorhead6]

Originally Posted by 55Brodie

Actually, dwell is the angle measurement in degrees of camshaft rotation that the contact points remain closed. A larger dwell angle equals less gap and allows the coil to fully saturate.

Perhaps. I am working on a Mustang distributor today and will be setting it up in a day or two. I will double check that.

In any case, go with the dwell reading and remember to check the timing. VR, JT

[V8 Bob]

Originally Posted by 55Brodie

Actually, dwell is the angle measurement in degrees of camshaft rotation that the contact points remain closed. A larger dwell angle equals less gap and allows the coil to fully saturate.

Correct. Additionally, dwell directly affects timing, so unless the dwell is kept constant, the timing will vary several degrees advanced or retarded.
JFYI, the target dwell for all single point Ford distributors is 27 degrees. The engine will run best at this setting.

[55Brodie]

Thanks Bob....I didn't want to get into a whizzing contest with Motorhead.

[Motorhead6]

Originally Posted by 55Brodie

Thanks Bob....I didn't want to get into a whizzing contest with Motorhead.

No whizzing contest. Didn't mean to step on anyone's toes here. You are correct, I had it backwards; opening the points decreases the dwell.

[Motorhead6]

My experience yesterday. Changed the points and found that the dwell was too low. Widened the gap and the dwell increased and the timing advanced the same number of degrees that the dwell increased. Sorry for the confusion.

[55Brodie]

For some reason your dwell meter reads bass-ackwards.

[Motorhead6]

It does sound that way. I know dwell is supposedly the measurement of coil saturation; points closed. That said, opening the gap should reduce that saturation period. Just passing on what I observed. It is an old meter, but the engine runs better at the reading and the points are at about .020" gap and dwell is 26 degrees. Had it at .016" and didn't run so well and the dwell was at about 19 degrees. Could be that it runs better because when I changed the dwell that the timing came into spec.

I guess the point remains that the better way to set the points is with the dwell meter.

[55Brodie]

Agreed, feeler gauges are notoriously inaccurate and subjective. BTW, thar famous auction site usually has a selection of old hand-held dwell meters for reasonable money.