Setting Dwell

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72Plymouth

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Ok I finally checked the dwell. Wanted to know exactly how to read it on this meter. The first photo shows about 750 RPM idling in park after I warmed it up. The Dwell reads at about 26 degrees on the second photo.

The book calls for 30 to 34 degrees on a 318. Should I re-adjust the point gap? If so would I widen the gap since it is lower than specs? I didn't disconnect the vacuum advance from the distributor. Will this make a difference?

I set the timing at TDC about a month ago if this matters.



Thanks.
 

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Dwell isn't adjustable with electronic ignition. Been a looooong time since I've messed with points but I think dwell is the amount of time in degrees that the coil is becoming saturated, which happens when the points are closed. So, I think, to increase dwell you would reduce the point gap.
 
Dwell isn't adjustable with electronic ignition. Been a looooong time since I've messed with points but I think dwell is the amount of time in degrees that the coil is becoming saturated, which happens when the points are closed. So, I think, to increase dwell you would reduce the point gap.

"Correcto mungo" 64 Cuda.
 
I thought I was right but it just seemed wrong that his dwell would be less than spec. As the rubbing block wears the point gap should close, increasing dwell. So why is his dwell less than spec? Somebody could have put the points in with the wrong gap (very possible) or I guess something funky could be going on with metal transfer between the points surfaces. Gee, this stuff is fun! And I remember when I ran dual points & solid lifters & fenderwell headers & an open hood scoop on my daily driver. Ahhh, the good old days!
 
My guess is they were set with a feeler gauge or by guess.
 
The thing about dwell.

First, most Mopar single point dist's are well, junk. Sorry.

This IS a 'little wide' if the dist. is tight. First thing to do is make sure there's a tiny amount of lube on the "approach" side of the rubbing block. Good quality point sets, like Blue Streak, used to come with a tiny capsule of lube

Next, while watching the meter, gently rev the engine up to high RPM and back, both with the vacuum advance connected, and also disconnected. See what the dwell changes and I'll bet it does.

Depending on this operational change, and how loose the dist. is, you'll have to average out the change and decide where to finally set the dwell

Always set the dwell a little on the wide side to allow for wear, always apply a little lube, always check and reset it after a thousand miles or so,

and ALWAYS set the timing AFTER you adjust the points Points wearing closed will retard timing
 
My guess is they were set with a feeler gauge or by guess.

Yup! I did set the gap with a feeler gauge at about 0.018" so it's between the specs of 0.014" to 0.019". Earlier, I didn't know I was supposed to check the dwell after.
 
The thing about dwell.

First, most Mopar single point dist's are well, junk. Sorry.

This IS a 'little wide' if the dist. is tight. First thing to do is make sure there's a tiny amount of lube on the "approach" side of the rubbing block. Good quality point sets, like Blue Streak, used to come with a tiny capsule of lube

Next, while watching the meter, gently rev the engine up to high RPM and back, both with the vacuum advance connected, and also disconnected. See what the dwell changes and I'll bet it does.

Depending on this operational change, and how loose the dist. is, you'll have to average out the change and decide where to finally set the dwell

Always set the dwell a little on the wide side to allow for wear, always apply a little lube, always check and reset it after a thousand miles or so,

and ALWAYS set the timing AFTER you adjust the points Points wearing closed will retard timing

Well I'm almost positive this is the original distributor, so maybe it's worn out. I did check and rev the motor while the dwell setting was on and it didn't fluctuate but I can double check. The vacuum advance was connected. Don't even know if that works though because it's so old.
 
Now I'm thinking that since the dwell is so off, the timing is not really at TDC as it shows because I read that every 2 degrees the dwell is off, the timing is one degree off too.
 
If you set the timing with a light, the timing is where it's at, regardless of dwell. However, if you were to now CHANGE the dwell/ point gap WITHOUT resetting the timing, it would be off. By the way, I would not set the thing at TDC even if that's what the sticker calls for. Bump the thing up to about 5BTC at least

"Back then" I never used to set single points by gauge, just "eyeball" them, then check the dwell ON THE STARTER. When I thought I had it close, then I'd put the cap back on, start the car, and recheck again. If it was OK, I'd set the timing

Both my sixpack and later my 340 had dual points, so they were a little different. Yup. I just HAD to fall into the trap of aftermarket CDI ignitions, there were a few back then. "Tiger" and another, at least one of 'em came in a kit. You could not get a tach to operate to save your - - -

In my '70RR which had the Rally dash, I installed a Jones/ Motrola mechanical drive tach behind the dash in the "clock" hole. Got that dist out of a hemi for 25 bucks!!!
 
A lot of people had no idea how to set the dwell on a dual point distributor. In reality, it took a little longer, but was simple once you knew the main trick, which was block one set of points open with a piece of cardboard, then set the unblocked set, then reverse where the cardboard was, set the others and if you had them both spot on, when you unblocked the other set and ran with them both, it was spot on.

FF
 
A lot of people had no idea how to set the dwell on a dual point distributor. In reality, it took a little longer, but was simple once you knew the main trick, which was block one set of points open with a piece of cardboard, then set the unblocked set, then reverse where the cardboard was, set the others and if you had them both spot on, when you unblocked the other set and ran with them both, it was spot on.

FF

I didn't do it that way. I just set the primary set with the secondary blocked, then set the secondary for total dwell. Once you've done it a few times, and I'll admit, much easier on a BB/ RB, it only takes a couple of minutes I used to run ONLY either Blue Streak or whatever Echlin called their super duper points. Accell had points too, but got a rep for the springs being TOO stiff for street use--allegedly caused wear on the dist.
 
....I just HAD to fall into the trap of aftermarket CDI ignitions, there were a few back then. "Tiger" and another, at least one of 'em came in a kit. You could not get a tach to operate to save your - - -

When I bought my '64 Barracuda in 1974 it had an add-on CD ignition. That fall I took auto shop in high school. One day I was outside of the shop trying to start my car & it just kept cranking & cranking but barely fired. The instructor came out & told me I was going to burn up my starter. We messed with the car a bit & ended up bypassing the CD ignition. Never had a problem after that. Don't remember what brand it was but it was a finned aluminum box that was kind of orange & about 3"x3"x5". Thankfully the electronics these days are a lot better.
 
Thanks guys. Gonna adjust the points and try to get em in the ballpark specs. Then I'll check the idle speed and set the timing.
 
A little off-topic, but if a daily driver that you are buying gas regularly to drive, electronic ignition is the way to go and will soon pay for itself in less gas, plus improve performance and reduced emissions. Not much harder than replacing the points and you are done for life. You can install the Pertronix Ignitor or Crane Cams XR700 in your existing distributor. I bought one of the later for ~$25 on ebay recently. I also see the Mopar setup (elec. distributor and box) sometimes on ebay sell for ~$80. Points are archaic and always problematic. I just keep them in the trunk in case I have to revert on the roadside. Never have in decades of driving.
 
'64 Cuda,

My '65 Newport had the Delta CD ignition box, yellow finned aluminum. They probably sold a lot of them in J.C. Whitney. It also seemed to act erratic. It had a toggle button on the side you could press in to bypass, and the car ran better straight off the points. Strange that they used ~22 awg ribbon cable for the wiring. I replaced it with the Crane XR700 ~1995.
 
I agree with Bill, I'd buy a Pertronix conversion and forget about points and dwell forever! Here is one, slightly used, going for about half of new...

Ebay link
 
'64 Cuda,

My '65 Newport had the Delta CD ignition box, yellow finned aluminum. They probably sold a lot of them in J.C. Whitney. It also seemed to act erratic. It had a toggle button on the side you could press in to bypass, and the car ran better straight off the points. Strange that they used ~22 awg ribbon cable for the wiring. I replaced it with the Crane XR700 ~1995.

Don't know what brand mine was but there wasn't any togggle switch. It had a big transistor on the side or top, don't recall. It had flat pieces of stuff like printed circuit board on the ends of the wires (might have been ribbon cable) that connected it to the coil. IIRC it had black thumb wheels on the coil connections & we spun them off & reconnected the old wires back to the coil. Of course, that was about 35 years ago so my memory is a bit fuzzy. I trashed it & didn't look back. Later switched it over to a factory Prestolite dual point distributor that turned into a small diagnostic nightmare.
 
The dwell setting on Mopar electronic distributors most certainly IS adjustable. It is called "air gap" adjustment and is set using a non magnetic feeler gauge. While there is no "dwell" specification in the book, there is an air gap specification and changing the air gap spec most certainly changes dwell. I have a set of brass feeler gauger just for the occasion.
 
The dwell setting on Mopar electronic distributors most certainly IS adjustable..

It most certainly is NOT adjustable!!! The air gap has no effect on dwell, all the dist. does is to trigger the box.
 
K. I adjusted the idle to 750 RPM in neutral. The point gap was tricky to get right. Every thousandth of an inch made a big difference. First I got the points to line up with the high point lobe on the cam.

I widened the gap a couple times. It got worse, a couple of the times it wouldn't start. When it was too wide, the dwell read way lower around 10-12 and the motor sounded bad and was pinging a lot so I turned it off quick.

I made the points gap smaller and it ran better and finally got the dwell up to about 31 degrees. I left it there and changed the idle speed again to 750. Then I got the timing light and saw that it was retarded about 8 degrees ATDC. So adjusted the timing to about 4 degrees BTDC. Sounds pretty good now and runs better.

One problem is that the tach on the Tach/Dwell meter reads differently than my Autometer inside the car. They have about a 100 RPM difference! So this is obviously going make a difference when timing the car. I decided to use the Autometer to set the idle at 750 but since the other meter is off, the dwell reading is probably not right either. O well! Will go electronic sooner or later. Thanks for the help guys!
 
Don't know what brand mine was but there wasn't any togggle switch. It had a big transistor on the side or top, don't recall. It had flat pieces of stuff like printed circuit board on the ends of the wires (might have been ribbon cable) that connected it to the coil. IIRC it had black thumb wheels on the coil connections & we spun them off & reconnected the old wires back to the coil. Of course, that was about 35 years ago so my memory is a bit fuzzy. I trashed it & didn't look back. Later switched it over to a factory Prestolite dual point distributor that turned into a small diagnostic nightmare.

Sounds like the same Delta box. Mine also had the green mini-circuit boards at the coil connectors, with big black thumbscrews, and the exposed TO-3 transistor on the box. The bypass switch was a little red square on the left side. Good you didn't find it because it never had definite feel that it was toggled in or out. Better to bypass it at the coil like you did.

BTW, while on add-on boxes, I picked up an interesting one cheap on ebay - MSD PN7000 Stacker, sold new by a surplus outfit. You hook across the coil and it senses when your regular ignition fires and adds a CD multi-spark to it. It works with either points or electronic ignitions. They had a whole line, including some boxes for distributor-less cars, but appear to have dropped them. I haven't tried it yet, maybe I'll see why.
 
K.

One problem is that the tach on the Tach/Dwell meter reads differently than my Autometer inside the car. They have about a 100 RPM difference! So this is obviously going make a difference when timing the car. I decided to use the Autometer to set the idle at 750 but since the other meter is off, the dwell reading is probably not right either. O well! Will go electronic sooner or later. Thanks for the help guys!

One thing you may want to check anytime before you use the meter is to make sure it is zeroed out. With it off you can adjust the needle to zero it with the screw in the middle at the bottom.
 
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