Questions on Dwell

[51woodie]

I was out for an afternoon drive in my '46 Coupe, 59AB, and it began to run rough. Missing on acceleration, and not revving as it should. Time to go home! The next day, I pulled the distributor, and found the condenser was open when tested with the ohmmeter. I installed a condenser I had purchased from Tubman, on spec that I would need it one day. As I don't have a machine to test my distributer, I checked the point gaps, both at +/- .015", and installed the unit. Out of curiosity, I wanted to test the dwell to see what it was. Two question came up when I connected the leads from the dwell meter.
1. What is the correct dwell? I did searches and just got confused.
2. When I connect - to coil + to ground, I get 42 deg.
When I connect + to coil - to ground, I get 48 deg.

What should the dwell be, and why the difference when polarity on the connections are reversed?
Took the car for a test drive, and it runs like Henry built it. I sure wouldn't want to do a condenser change on the side of the road!

 

[Bored&Stroked]

As these distributors have TWO sets of points (that work in unison), you have to block off the set on the passenger side first (piece of stiff cardboard - .025 thick or so), then you check/set the dwell on the driver's side first - at 22.5 degrees. Once this is done, then you take the cardboard out and set the total dwell (both points) to 36 total degrees.

I don't know on your meter how to use the leads. You'd need to ask them.

 

[51woodie]

Bored and Stroked. You are funny. I asked the dwell meter, and it said to ask someone that knows. You got a red clip and a black clip, figure it out. I don't have a distributor machine, so I can only go old school, set the points and put it on the engine. The engine idles nice and steady at 500RPM, pulls good and has a nice steady vacuum at idle. So 42 deg. is not good?

 

[Will D]

I cobbled together a device that helps in setting dwell. Base is made of plywood and the degree wheel has an offset notch for rear of distributor to set into. Glued a piece of paper with degree markings. After setting the timing using the ruler method on vanpelt website and adjusting both sets of points to .015 gap, Spin the degree wheel with multi meter(continuity setting) connected and piece of paper to block off one set of points and re adjust Gap to get the correct dwell. Repeat with second set of points.

 

[tubman]

Bored and Stroked. You are funny. I asked the dwell meter, and it said to ask someone that knows. You got a red clip and a black clip, figure it out. I don't have a distributor machine, so I can only go old school, set the points and put it on the engine. The engine idles nice and steady at 500RPM, pulls good and has a nice steady vacuum at idle. So 42 deg. is not good?

If it runs as well as you say, 42 degrees seems to be good. How accurate is the dwell meter?

 

[51woodie]

Will. Yours is a bit more advanced that the jig I built. The one I made has the body sitting in a bored hole in a wood block, and there is a slot for the shaft to fit into. One ear of the body comes up against a stop block (bottom left on the block) when the housing is rotated to the right, and that is where the left set of points are just opening. It works for me, but now I think I may make one like yours.

 

[Bill OH]

I have a Snap-on Dwell-Tach with the leads being black and yellow. I connect the yellow lead to ground and the black lead to the terminal for the coil- condenser. Reverse the leads and no reading. I have the helmet distributor with a lead from the coil- condenser terminal extended and zip tied to the spark plug conduit and I can easily connect the dwell tach. I just checked the dwell - 36 degs after 5k miles.

 

[Bored&Stroked]

Bored and Stroked. You are funny. I asked the dwell meter, and it said to ask someone that knows. You got a red clip and a black clip, figure it out. I don't have a distributor machine, so I can only go old school, set the points and put it on the engine. The engine idles nice and steady at 500RPM, pulls good and has a nice steady vacuum at idle. So 42 deg. is not good?

I guess you are funny too. You don't need a distributor machine to setup the points as I mentioned above. You can do exactly as I said - while cranking the engine over (even though it is a bit "crowded" in the front of the engine and you have a fan that needs to be removed). This is how "old school" did it when using a dwell meter - with the distributor in the car. Now - if you're doing it on the bench with point-gap, then you get what you get in the end . . .

Your current dwell of 42 is a combined dwell of both points . . . if it runs fine and you're happy, then so be it. However, if you want to setup the dwell as it should be setup . . . then I've explained how.

 

[51woodie]

After reading the above posts, I decided to buy a new meter that included measuring dwell, as the one I have is near 50 years old. The new one is an INNOVA 3340 digital unit, and came with a clamp-on for reading current, as well as a temperature probe.

The dwell reading I got on the new meter was 37 deg., as opposed to the 42 deg. that I got on the old meter. Must be some aging issues with the components in the old meter. Also, unlike the old meter, it is polarity sensitive, and will not give a readout if connected incorrectly.

 

[Bored&Stroked]

Good news . . . sounds like you have the dwell as close as you'll probably get it to being the correct total.

You'll still not know the dwell of the driver/passenger points individually, but that takes a bit more work in a hard to reach place.

You mentioned that the car is running correctly again - do you attribute that to the new condenser? That would be my guess!

 

[51woodie]

Yes, the condenser was the problem, and a Tubman unit solved the poor running issue. If all goes according to posts I’ve read about the Tubman condenser, I’ll never have to change it out due to failure.