The Stovebolt Site Forums The Shop Area Engine Shop Adjusting Dwell - '54 3100 six

I only post this question after researching here and beyond. Simply put, how do I adjust the dwell on my '54 3100 with original six. PO switched from 6 volts to 12 volts, but still running 6v coil. Also, published dwell angle is 38-45. Is anywhere in this range ok, or is there a more accurate recommendation?

Explained here: https://www.stovebolt.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=686472

Getting hung up on a dwell reading is wasted effort. Set the point gap to the specification the distributor serial number calls for (not the year of the vehicle or the engine), set the spark timing, and drive on. There's no telling how often a stovebolt distributor has been changed over 70 years or so, and not all distributors have the same dwell specification.
Jerry

There’s a wrinkle I never knew about. Where would a guy find points gap by distributor serial info?

I actually did set my gap via dwell last time I did it. I thought it worked pretty slick but I may have just gotten lucky.

Thank you G&F for the link and info, that's one I didn't see in my research on this forum. And thank you HrLincoln, valuable info as always.
However, I'm still stuck with the basic question of "How do you adjust the dwell setting?" Still on that quest....

Adjusting dwell is easy enough but as HRL pointed out, it’s not necessary on these engines. Hook up your dwell meter per instructions with the instrument. Remove the distributor cap and set it off to the side. Remove the rotor. Loosen the point hold down screw slightly and have someone crank the engine while you use your screwdriver to move the point adjustment slightyone way or the other until you get the reading you desire. Tighten the points and reinstall everything. Start the engine and see how well you did. Warning, you can chase the adjustment all day if you have a worn out distributor shaft/bushing. Good luck.

I’d have to go verify, but fairly certain I set my 235 dwell at 31 degrees.

Spec is 31-35 from what I looked up. Went to the numerically low side of the range so that it’s still in spec as the rubbing block wears.

I would be more concerned with using a 6 volt coil with a 12 volt system than what the dwell is. The proper way for a 12 volt system to work is with a ballast resistor and a 12 volt coil designed for that system. You are likely not getting the correct voltage for the engine to run properly.
Fred

Thanks rfs56trk. Interesting. Had a new 12v coil installed and the new points got burned pretty bad. Assumed might be the 12v coil, so reinstalled the 6v and it started up ok.
Would be interested to know if ya'll think the coil could have burned the points up.

Putting 12 volts to a 6 volt coil is a guaranteed way to burn the points, as the coil is designed to work properly at 7.5 volts (charging system voltage with the engine running, against a fully charged 6V battery). A 12V GM coil operates properly at around 9.5-10 volts, and is designed to use a resistor to drop the charging system voltage (14.7 or so) to the lower voltage. During engine cranking on a 12V system, a bypass circuit allows the coil to run on straightr battery voltaqe. Simply swapping coils is not sufficient to make a 6V-12V conversion of the ignition system.

A dwell meter is nothing but a voltmeter with a specially calibrated meter movement. It is actually measuring an averqge of "points closed" voltage measured downstream of the coil (zero volts) and "points open" voltage which is the same as battery voltage. Changing the amount of time the points remain closed alters the apparent voltage the meter sees.

Around the time Chevy switched from a 6V to a 12V ignition system, they changed the profile of the distributor cam, and also changed the specification for the dwell setting. The point gqap also changed, from .016" to .019", which accounts for the difference in dwell. For instance, a 1954 standard transmission distributor, P/N 1112388 calls fpor 38-45 degrees of dwell. A 1955-56 distributor P/N 1112403 calls for 28-33 degrees. All of the rest of the 12V distributors call for the lower setting. The 1112403 distributor is specified for all 6 cylinder passenger cars through 1962 according to my Motr Magazine service manual. Truck distributors might have a dirfferent part number.
Jerry

Just to answer the direct question, how do I adjust dwell:

Adjusting the points gap adjusts the dwell.

Dwell is an indirect indicator of point gap.

Dwell is an indirect indicator of point gap.[/quote]

Yes. If the gap is correct the dwell will be also.
A dwell meter is a good way to check the gap before you open any thing up. Hook it up & start the engine.
George

There is a direct correlation between gap and dwell. If you get the gap right the dwell will be right. I've seen people use the flap from the cardboard carton that the new points came in as a feeler gauge. One thing to note, if you adjust the points to the correct gap and then tighten the clamp screw, the gap will change. You have to learn how much it changes then initially set the gap off by that much so it will be correct after you clamp it down. Always check after you tighten the screw.

Thank you Lincoln for the info. Always learn from what you post.
What's not clear to me is if you believe the new 12v coil I installed caused the new points to burn.
As background, truck has been sitting for a few years after uncle became ill. I acquired the truck from his widow and my cousins. He had the system switched over to 12v from 6v, and drove it for years afterwards. I do not know what exactly had been done in the 6v->12v conversion, but know my uncle was a man who would have done it "right".
After replacing the complete fuel system I then turned to the ignition system and replaced with new components: plugs, wires, distributor cap, rotor, points, condenser.....and coil. I replaced the 6v coil he had on the truck with a new 12v coil - the only "change" from what was installed. The truck started right up and idled for 20 minutes or so and it started sputtering and died. I don't know at this point if it died from fuel or spark. At that point it wouldn't start back up. I eventually decided to replace - again, the points and condenser. It was then that I discovered the badly burned points. The plastic on the arm of the points had even melted some and the arm showed signs of being overheated. Thinking that the 12v coil could have burned the points, I reinstalled the 6v coil to see if it would start. After replacing the points, condenser and reinstalling the 6v coil the engine started.
So, I'm wondering if the 6v coil is the correct coil to be using with this system that has been converted from 6v to 12v? Or, is the 12v coil correct, and try it again and see if it burns the points again. Your knowledge here would be greatly appreciated.

Leave the coil alone! If it ran for years with it then it must be right.

Before playing "musical chairs" with parts again, How about doing some tests with a voltmeter and/or an ammeter? Points can handle a maximum current flow of about 5 amps without burning out prematurely. 3 1/2 to 4 amps is better. Some "12 volt" coils are intended to run without a resistor. Ford usually ran coils that had the proper primary circuit resistance to allow the points to have a reasonable life span without needing an external resistor- - - - -They were willing to accept a reduction in firing voltage during a cold start in exchange for longer point life. GM and Chrysler took the other approach- - - -Use a lower resistance coil primary winding for a hot spark while cranking, and protect the points with a voltage-dropping resistor during normal running with the charging system operating. There's no "right" way to do it- - - - -Just use the proper combination of parts and accept the downside that comes with either choice.

On a stovebolt six running a 12V system, I'd choose to use the coil and ballast resistor listed to fit a 55-64 Chevy V8 passenger car, and the foot switch on the starter with the small side terminal to bypass the resistor during starting. All those parts are designed to work together, and there's no guesswork about coil voltage. As usual, there are two kinds of ignition parts- - - -original equipment Delco-Remy (NOT AC-Delco) and "wrong"! NAPA "Echlin" brand ignition parts or "Blue Streak" are the top of the line where non-GM replacement parts are concerned.
Jerry

JimboTX
Nowhere is your discussion did you indicate that this "6V to 12V conversion" had a ballast resistor installed. Or during replacing parts was it mentioned. HRL is spot on if you want this truck to run correctly.
Note: Buy a ballast resistor for a late 50's truck and a 12 volt coil that has the words stamped on it: For use with external resistor.
Fred

Fred, both the previous 6v coil and the new 12v coil I installed have ballast resistors. When I bought the new one, I made sure I got 12v with resistor. When I reinstalled the 6v, I put the old resistor back on.

Hanks custodian The best way to adjust dwell on a stovebolt is with an HEI !! You'll have real, dependable, long running ignition repairs are available at any parts store. Keep a pickup coil in the glovebox and a little handful of tools so you can change it !! Build your own HEI so you understand what it takes,it's pretty simple with tools you already have on your bench.

Granpa49 Sounds like you have been there and done that !! I done it years ago,glad there is so much better equipment out there today ! For people who enjoy conquering antiques go for it !!!

OK, but maybe I'm missing something in your explanation. I was not referring to a coil with a built in resistor. You need a separate external ballast resistor.
And the external resistor should not be mounted on the coil or the engine as there is too much heat produced.
It should be mounted on the firewall so the heat can be dissipated.
Fred

Time to back out of this equine flagellation- - - - - -"My mind is made up- - - - -don't confuse me with facts!"
Jerry

😂

Jerry,
You have my vote.
Fred

JimboTX You could solve a lot of problems with an HEI,lot better ignition,easy to work on,can buy anything you need at any parts store,eliminate that point wear-out,plus it'll start easier and better.

JimboTX HEI

"Good Grief, Charley Brown!"

Jimbo TX replied

So much fun and so little to understand. "Dwell" what is it? Actually a rough measurement for coil saturation. The magnetic field must build up and then collapse. Spark!. The points are...a switch. On-off. Points closed? Current in coil, field builds.. Points open? Field collapses, spark. Fancy word for this is..induction. So, dwell angle. Camshaft way to say, "how many degrees are the points closed. That depends on a few things. 1, shape of the cam.How much lift is there and what is the ramp? Camshaft stuff. Can points "bounce"? Yes. So, the shape matters. 2, How many times will that switch open and close for a given amount of time? and how long will that switch be closed? Depends. How much current will the switch handle? How much will the coil take? An amusing observation: 4 cylinders? 45 degrees dwell. 6 cylinders? 40 degrees dwell. 8 cylinders? 30-35 degrees dwell. Notice anything? Back to #1, Point gap matters. So far Hotrod has the practical grasp. You and me get to work with what the Engineer and the Manufacture gave us. So, sometime in the distant past, some guy with a slide rule found out how much current the switch that the Accountant let him use would take over time. Sneaky guy he was, he added a Capacitor(Condenser for us car/truck folks) Just a few pennies he got past that Accountant. So, for a simple recap, the cam shape depends on the Dist. PN. Hotrod got that too. Now on, to coils. . Some guy had to figure how many turns and how big the wire was gonna be in the coild(Enter Mr Accountant again) Moe math and more current calculations, Done. For a 4 cyl motor. Mr accountant approves. Then someone said 6 cyl, and instead of more math, we just, use the same coil and switch. Now someone gets creative. 8 cyl and 12 volts. Take that Mr. Accountant. So we get The "Ballast" resistor. Current is controlled. Switch still works and no money was spent on Math. Then someone decided to put that resistor inside the coil. And we start the confusion all over again. Now we have a true 12 volt coil. May your morning be well caffeinated. Enjoy. Shout out to Hotrod. Just set the gap according to the PN. You got it.