Ignition work

[Gordon Maney]

I had a conversation with someone today about point gap and dwell angle. Dwell angle is determined by point gap. If you change dwell angle, you accomplish that by changing point gap.

Point gap is the measured distance between the ignition points when the rubbing block is on a high point of the distributor cam, for reference.

Lots of people don't have dwell meters, and it seems there is little use for them anymore on newer machinery.

What are you doing? Do you simply set your points and then the timing, or do you have a dwell meter?

I remember my father did not have a timing light. He practiced what he called road timing.

[W_A_Watson_II]

I have a dwell meter, but the last three sets I replaced I set by eye. the tractor and trucks all ran fine, probably not optimal but they worked.

[Gordon Maney]

I have a dwell meter, but the last three sets I replaced I set by eye. the tractor and trucks all ran fine, probably not optimal but they worked.

By eye, you mean with a feeler gauge, or literally by eye?

When I was a mechanic at an IH dealership I did so many tuneups I got to recognize the gap size that yielded the dwell angle I wanted and truly did set them by eye, at least initially. We used a beautiful Sun scope then, so I used it to verify. Typically it was correct. Those were the days.

[W_A_Watson_II]

Yep, truly by eye, no gauge. I did the Farmall Super-C, the 46 PW and the 361 in the W500 in the past three years.

[iranch]

I set them by sight also and it usually works fine. Some of the clunkers I keep running around this place require a dwell meter though. The distributors are so worn that you have to shoot for a running average. A lot of the Delco distributors from the 50s and 60s don't have bushings, the housing has to be machined to accept one the a bushing made. Replacement shafts or new units are hard to come by, so I just wing it.

Dennis

[Gordon Maney]

Dwell angle is a compromise of a sort. If it is too small, a result of the gap being too large, the available voltage will be too low. You may miss under load, or not fire a plug that has an enlarged gap.

If you make the dwell angle too large, the result of a small gap, you get great available voltage, but you also get a reduced point life.

If the shaft bushings are too loose you get what is called variation in dwell. If it is bad enough it may not want to idle very well.

[iranch]

Loose shaft bushings

You also have to have the magic touch to get them started when they are worn. It's amazing how well they will run at a specific RPM (a lot of farm work is constant) range if you use a dwell meter and set the points at that RPM. If not it's time to dig around in the shop and see if you can find one that's a little bit better, never throw anything away.

Dennis

Time for bed, I'm rambling.

[DrPepper]

Lots of GM distributors are set with a dwell meter...

60' - 80's...??? there is a door that lifts on the dist cap and you use an allen wrench (I still have my spring screwdriver special) to set the dwell while it is running. Ahhh, trivial persuit....
DrPepper

[Gordon Maney]

60' - 80's...??? there is a door that lifts on the dist cap and you use an allen wrench (I still have my spring screwdriver special) to set the dwell while it is running. Ahhh, trivial persuit....
DrPepper

Yes, that was a great idea. GM had the best idea at that time.

[DrPepper]

On to the next level....dual points...!

Anyone remember the two set ups available...?
1, 4 lobe cam on a V8 with the points set 90 degrees apart so you had a better cam profile. Each set fired four cylinders.
...or...
2, Two sets of points, wired in parallel and slightly overlapping each other to increase dwell, you could go mad setting these up.

DrP

[Gordon Maney]

In my automotive program I had a Sun distributor machine. That worked great for dual point distributors.

You blocked a set of points open with a small piece of card stock or match book cover and adjusted the other set. Then you moved the piece of card stock to the other set and repeated the process. I never had to do one of those any other way. Lots of motorcycles had dual points.

One day we might be at the living history farm demonstrating the old ways. Setting ignition points.

[DrPepper]

Sun machine!!...Hey, that's cheatin'....

Only saw them and never actually got to use one. Then again, I didn't have to R&R the distributor to set the points.

Thanks,
DrP