I inherited an older tach/dwell meter from my brother; it only has 2 leads/clips, 1 red, 1 black. How do I hook it up to check my tach? (I understand tach, but what is the "dwell"?). Thanks in advance! Brian

 

Back when trucks had points you could adjust, dwell angle was what you gapped your points at. The greater the dwell, the longer the points stayed closed,(conducting electricity). On your tester the black lead goes to ground, the red lead went to the tach lead on your coil. First you set your idle, then noted what your dwell was and, (on Fords), turned your truck off, popped the dizzy cap and set your points. It was kind of a trial and error thing untill you got the hang of it. Che@#y's and othe GM's had a nice little door on the cap that used a dwell tool. Looked like a hex head bit on the end of a flexible spring. You could set dwell with the engine running.

 

Hook the Red clip to the negative "-" side of the coil and the Black clip to a good ground (like the "-" side of the battery).

Dwell is the time that the points are closed (and charging the coil)measured in crankshaft degrees. A V8 engine theoretically has a maximum of 45 degrees - but in reality a single points system runs 28-32 degrees and a dual point system runs 38-42 degrees of dwell.

 

Initial bad info on this reply has been edited out to avoid confusion

On Fords anyway. Kind of off topic, but a trick we used to do was take the points apart and bend the spring back to gain a bit more tension against the lobe. Friction wore them out a little sooner, but you got a few more rpm's out before floating. Won't be long before the question will be, "what are points."

 

The trouble with maximizing out the dwell is that as the point rubbing block wore the dwell increased. As the point contact surfaces wore the dwell decreased. It was a race...

When the dwell changed the timing changed.

 

As has been previously stated, dwell angle is the number of degrees that the ignition points are closed during each piston cycle. This closing time allows the coil to charge, and when the points open, the spark is generated. Therefore, the longer (greater) the closing time or dwell, the greater the spark. When I used to set up my 312 Y-block, I would set the dwell at 26 degrees. The spec was 26-28. By setting it at 26, then when the point contact block wore down, the dwell would increase , but still be in spec. As the dwell increased, the timing retarded, I believe for each 2 degrees of increased dwell, the ignition timing would retard 1 degree.
At any rate, with the new electronics, this stuff is now a thing of the past. I still have my dwell/tach and timing light, but haven't used them in years. Kinda too bad. I sort of miss tuning the old Fords.

 

I used to like to point a timiing light at the fan and watch it.
Jim

 

There was an old rule-of-thumb that the points wear .001" for every 1000 miles.

Here's a neat article that shows just how useful a dwell meter can still be today.

http://www.geocities.com/Athens/Olym...car_info27.htm

Barry

 

Hey Barry Very good article , the things you can learn on here are endless. And who says you can't teach old dogs new tricks.

 

Ponts were simple but the electronic systems are much better. Damn but I changed out a lot of points...

Interesting article. Some of the older "period" shop manuals explain some of the interesting dwell meter uses.