Ok JunkYardDog I guess if the lobe of the distributor cam is flat or rounded off from wear the dwell angle would be less or more?..... Is the dwell angle the measurement of the degrees whilst the points are closed? or is it whilst the points are open?
I guess I never had a distributor worn that badly, I have had one to lock up the advance mechanisum inside once.
I haven't seen a GM manual for breaker point ignitions that showed setting points with a dwell meter, the newest one I worked on was a 73 Caddy. I guess they figured their mechanics didn't need one?
I saw my first dwell meter when I first went into a Halliburton shop. That Shop Foreman had everything from a new Sun machine to a engine O-Scope. He could make those old Gasoline Roadbinders purr like a fat cat! One of his favorite tools was a vacuum meter.

Hey Macky Wacky......haven't you been paying attention? In a posting above it states: "The dwell angle is the number of degrees of rotation of the cam/distributor during which the points are closed." So, to use your own terminology.......DUH!

Most of the older distributors have cam lobe wear. One or two degrees cam lobe wear is acceptable and most of the older distributors fall within that specification. If you put your 1928 distributor on a distributor machine you will probably find that the cam lobe does have one or two degrees wear if it has an original cam. Even with only one or two degrees of wear the point gap on each lobe will measure differently with a feeler gauge, that's why a dwell meter should be used because the dwell can be set to spec. as an overall average.

On the newer distributors like those used on the 327 and 350 engines from the late 1960's and early 1970's the distributor cap has a "dwell window" so that the dwell can be set while the car is running, and it is mentioned in some of the shop manuals to set the points by the dwell.

I just wanted to see if you really knew,

My instructions for engines with the distributor cap with the window said use an allen wrench to adjust the points whilst the engine was running, by engine sound, it didn't say anything about a dwell meter.

You can fool some of the people all the time, and you can fool all of the people some of the time, but you can't fool all of the people all of the time!

Wrong thread Macky Wacky. You need to move that one over to the General Discussion Forum under the "One Liner" topic. And, besides, that one liner has been used already.

Not Really, Doggie Doodle!

Can't wait for someone to remember to check the shaft bushing wear.

On the 1931 discussed above no shaft bushing was used in the distributor. On the older units the shaft turns on the cast iron housing.

To "Junkyard Dog":
I ran across a posting of yours regarding calibration of the dwell meter on a Sun 404 tester. You mentioned a procedure in the Sun Service Manual. Would you be willing to share that with me? I just bought a Sun 504, which I believe uses the same dwell unit, and I need to calibrate it.

Thanks, Ron
hestechearthlink

I will see if I can locate the information and then I will post it here.

Okay, for the Unit 50-1 Dwell and RPM unit here is the procedure for calibrating:

1. Turn U-50 selector knob to the 6 cylinder position.
2. Set the U-50 dwell calibrator knob on the front panel to 1/4 of its full clockwise range.
3. Adjust the U-50 6 cylinder rheostat (R7) on rear panel until the U-50 dwell meter reads on Set Line.
4. Attach the U-50 five prong plug into the five prong receptacle at the rear of the distributor tester.
5. Operate distributor tester at 1000 RPM and adjust breaker points in a distributor until U-50 dwell meter reads 22 1/2 degrees on the 45 degree scale. The distributor will now be adjusted to 50% of dwell.
6. Readjust U-50 dwell meter 6 cylinder rheostat (R7) until U-50 dwell meter reads 30 degrees on the 45 degree scale.
7. Reduce speed on distributor tester. Turn distributor tester to off.
8. Place U-50 selector knob in calibrate position. Place a jumper between dwell input leads (Terminals 1 & 2 on schematic). Adjust the U-50 calibrate control (R3) until U-50 meter reads on Set Line. Remove jumper.
9. Place U-50 selector knob in 8 cylinder position, and adjust the 4 and 8 cylinder calibrate control (R4) until U-50 dwell meter reads on Set Line.
10. With distributor tester operating, check for the following:

6 cylinder position 30 degrees on the 45 degree scale.
8 cylinder position 22 1/2 degrees on the 45 degree scale.
4 cylinder position 45 degrees on the 90 degree scale.

11. Remove U-50 five prong plug from the five prong receptacle at the rear of the distributor tester.

I learned this 27 years ago at the GM Trainning Center in Terrytown N.Y. I'll share this with everyone. It's a neat trick.
A very accurate way to check a dwell meter is to get an old GM computer command control carburetor car. Connect the red dwell lead to the large green mixture control dwell lead that is usually in the harness next to the carb and ground the black lead. Set the meter on the 6 cylinder scale. Jump the A-B terminals together on the diagnostic connector under the dash. Turn the ignition key to the on position.(do not start the car)The check engine light should begin to flash. You will hear the carb making a ticking sound. The sound is the mixture control solenoid pulsing the metering rods at a 50% duty cycle. This is extremely accurate.It is programmed into the computer. It should show 30 degrees of dwell. The math behind it is as follows.... 360 degrees in a cycle.. divided by 6 (6 cyl) = 60 degrees...at 50% on/off duty cycle = 30 degrees of dwell. Hope this helps.