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This is just a curiosity....

Why in '51 would a Delco-Remy distributor have a specifications for the dwell angle ranging from 21-30 degrees, but in '53 the dwell angle is very specific, 31 degrees?

When setting points with a dwell meter is it best to do this with the engine running? A couple of youtubers show doing it with the dist cap off and cranking the engine over to check dwell, but when I do it this way I get a different reading than when the engine is running.

Instructions for my analyzer, along with several online, say to check dwell with the engine running, which seems to make sense as it would provide a truer reading.

I've set my points at 31 degrees with the engine running and then adjusted the timing to 6 degrees again. I had to close the points from where I had set them to using my feeler gauge to get the reading to 31 degrees.

Is that with the advance disconnected?

It wasn't. I think Ross mentioned on another post, at idle there isn't enough vacuum on these ported systems to affect the vacuum advance when setting the timing. BUT, I think I should disconnect it and check it again as that could account for the difference. Thank you, that's a good observation.

Quote:

Everything is the same, vacuum line connected or disconnected. There is not enough vacuum at idle to affect the timing, as Ross suggested. But regardless the vacuum line shouldn't affect dwell, correct? Dwell affects timing, but timing doesn't affect dwell, correct?

I'm perplexed as to why dwell is different when running as opposed to when I set it just cranking the engine over with the dist cap off. (When I set it just cranking it over with the dist cap off it is very close to the .017" it's supposed to be.)

I had the machine shop fit new bushings and polish the shaft so it's not that I have a worn distributor.

Could it be something to do with my points? (NAPA) Maybe a weak spring so they are not closing as fast as they should? I've seen in the manual where they show how to test the tension of the points, so this was obviously something to be aware of, at least it was in '53.

I feel like either I'm not understanding something correctly, or something in my distributor is amiss.

Not sure if it has anything to do with the breaker plate spring and the speed distro is turning since that that plate springs are subject to centrifugal forces.

- Dwell is how long the points are closed.

- Timing is when the points open.

- Timing is set by the distributor rotation and the two advance mechanisms.

So if you change the dwell period the points will naturally open later and close sooner (to shorten dwell) or vice-versa. So, "open later" (or earlier) = we are also changing timing then.

But rotating the distributor or replacing a defective advance mechanism does nothing to change dwell, as dwell is set by the distance of the points from the cam. The closer the points are, the longer the cam pushes them open, and the longer the dwell.

You can buy a spring scale for cheap on Amazon. If the spring is too weak then the dwell will be excessively affected by engine sspeed. But you're also not really supposed to set the dwell just with the engine stationary. It should be checked while running and tuned accordingly.

Agree, there is no centrifugal forces at play, I was thinking something like point float, but that seems unlikely, especially at idle.

Maybe I'm trying to solve a mystery, but there's no mystery to be solved?