57J2Olds

Hello,

Can you please refresh my memory?

Do I set dwell first then timing?

My spec for dwell is 22 deg.

I'm running 25 degrees. Should I get it to 22? Positives and negative of leaving it this way?

Thanks

Lee

Vintage Chief

Always in this order:

(1) Dwell
(2) Timing
(3) A/F mixture

I can't speak to the specifics of your dwell & timing settings; but tuning an engine is always in the order I indicated.

57J2Olds

Thank you Sir!

Vintage Chief

Cheerio!

oldcutlass

I thought you had a 6 cylinder, if so the spec is 31-37* dwell. Dwell is always set before timing, dwell angle affects timing but timing does not effect dwell.

57J2Olds

So I tried to adjust dwell just now.

Now the car barely wants to start.

Like a low battery...........

Yes...It's a 49 six cyl motor.....maybe I should not have touched it...ughhhh

Can I please have step by step?

I was trying to hand turn flywheel to high point of cam lobe in distributer.

Vintage Chief

Vintage Chief

FWIW, a 1949 six cylinder tuning is identical to a 1948 tuning.

Charlie Jones

Dwell can be set while cranking.
Remove the cap and rotor, loosen the setscrew and nudge the points either way until the proper dwell is registered.

Sugar Bear

If setting dwell why look for the high spot on the distributor cam lobe? I'm not trying to be a wise guy; rather want to make sure that dwell angle and point gap spec. are not being confused.
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57J2Olds

I was setting point gap instead of dwell. It's been too many years since I dove into these old ones.

There are 2 set screws under the cap.

Which one is dwell?

Thanks

Charlie Jones

The point gap and dwell are the same thing.
If you set your point gap at .020 then the dwell meter should read between 31 and 37 degrees.
The screw that holds the points down to the plate can be loosened and the points moved to get the proper gap and or dwell.

57J2Olds

So if I set gap at .020 and my dwell is only 22 degrees what would the issue be?

Charlie Jones

Is this a six or eight cylinder engine that we are talking about?
If it's an eight cylinder engine then 22 degree dwell is just fine.

57J2Olds

The motor is a 1949 6 cyl

Sugar Bear

If the point gap and dwell are that close it could be the setting on the dwell meter. If the point contacts are badly pitted it can be way off when using a feeler gauge. If you trust the dwell meter use it before the feeler gauge because it will account for pitted/rough contacts.

57J2Olds

OK thanks.

I will look at this all again tonight.

VC455

As you realize, when you set the gap tighter than spec, the dwell will be less than spec also.
The problem with this is that there is less time for the coil to charge, and you may get misfire at higher rpm.
If you don't rev the engine into the upper ranges, you will notice no difference (except the coil will stay cooler, which is a good thing).

57J2Olds

I thought if you shrink the gap your dwell increases..???

VC455

I apologize. I answered quickly without putting my thoughts back in my teenage mechanic timeframe! You are correct.

As you close the gap, the dwell (the time the points stay closed) increases.

With longer dwell, coil heating will increase, which is not good for the coil.

And there will be less tolerance for point wear (the gap will close up faster as the rubbing block wears).

Otherwise, your performance will not change.

If you are asking about the apparent mismatch between expected dwell and point gap... If the points are used, they will have a rough surface, which will make the gap seem smaller when measured with a feeler gauge than the dwell would indicate.

With new points, the relationship between gap and dwell would be in the range shown in the specifications.

But really, 0.020" gap and 22° dwell isn't too far off.

Setting by dwell gives the most accuracy in every case.

Oldsguy

Dwell is the number of degrees (out of 360) during which the points are open and the coil is charging. So if you set the gap wider (static setting) then the dwell will be greater (dynamic measurement). Taking this to the absurd, if the gap were an inch (impossible) the dwell would be huge. Actually the coil doesn't charge but a voltage builds up in the windings and when the points close then that voltage is able to collapse and you get a high current pulse. We say charge but that really applies to capacitors not coils.

VC455

From https://www.howacarworks.com/ignitio...e-dwell-angle:

"A dwell meter ... registers the dwell angle - the period when they are closed."

Oldsguy

Thanks for that correction. I should keep my mouth shut as I truly feel I have forgotten too much. I used to teach that stuff you would think I would remember it...

Charlie Jones

FWIW I looked up a 1949 Olds six cylinder in my old Motor's Manual.
It shows a point gap of .022 and a dwell of 31 thru 37 degrees.
I agree that a dwell meter setting is more accurate than a point gap setting.

Sugar Bear

Does the dwell meter have a setting for the # of cylinders? Make sure it set to 6 cylinders.

Vintage Chief

Agree. Additionally, I'll add you need to ensure your meter is capable of being used on a 6V system (your 1949 straight 6 installed into a 1948 chassis should be a 6V system I do believe). The dwell meter should specifically state it will work on both a 6V & a 12V (negative ground) system. If it's only good on a 12V system, you'll need to use a 12V companion battery; then, there's the notion of whether your meter is a two-wire meter or a three-wire meter.

If you're trying to establish the point gap (which I believe you stated earlier) rather than a dwell meter, make certain the set screw holding the contact points to the distributor base plate is secured well. It's easy for the contact points to slip enough to throw off the contact point gap when you reassemble the distributor.

57J2Olds

I was thinking the same. I am using a Snap-on Model MT926A. There is only 2 wires on it. Black to ground and Yellow to Neg side of coil.

Is this my issue?

Vintage Chief

No idea. Evidently you have no instruction manual? A quick on-line search demonstrates a ~40 yr old meter - which is fine if it’s working condition and you know how to use it. A fair # for sale, saw a couple of instruction manuals for sale. Sorry, can’t help on model and/or usage but obviously it needs to be set correctly.