Distributor Dwell....

[Larry S.]

I have a 64 SB with a points distributor, and am looking for an explanation of "dwell" settings. I know that the dwell setting affects the timing, but dont understand what 30 deg dwell means in relation to say, 26 deg dwell?
Are the points set closer or further apart, at say 30 deg. vs 26 deg?
What does 30 deg relate to? ( Is it the number of degrees that the distributor turns with the points open or closed?)
My dwell tester show a drop from 30 deg. dwell at 900 rpm idle to about 27 deg at 2500 rpm. Is that about right or is there a problem?
Anyone got a complete explanation for me? Thanks in advance.

[Clem Z.]

Re: Distributor Dwell....

I have a 64 SB with a points distributor, and am looking for an explanation of "dwell" settings. I know that the dwell setting affects the timing, but dont understand what 30 deg dwell means in relation to say, 26 deg dwell?
Are the points set closer or further apart, at say 30 deg. vs 26 deg?
What does 30 deg relate to? ( Is it the number of degrees that the distributor turns with the points open or closed?)
My dwell tester show a drop from 30 deg. dwell at 900 rpm idle to about 27 deg at 2500 rpm. Is that about right or is there a problem?
Anyone got a complete explanation for me? Thanks in advance.

Explanation:
dwell: [1] In a contact breaker ignition system, the number of degrees the breaker cam rotates from the time the breaker points close until they open again. Also called the "dwell angle" or "dwell period."

[Larry S.]

Re: Distributor Dwell....

Thanks Clem. I appreciate that information.
Larry

[Duke W.]

Re: Distributor Dwell....

Dwell angle is the number degrees the points are closed, and I think it's crankshaft degrees, not distributor degrees, but I'm not absolutely positive. The typical dwell spec for an eight cylinder engine is 30 degrees and 60 degrees for a four-cylinder, so for the eight the points are closed 30 degrees and open for 60 for each 90 degree cylinder. One could measure it to be sure.

The narrower the point gap the higher the dwell and vice versa. If dwell decreases with engine speed the timing is advanced from what it should be because the points are opening early.

The GM spec for variation is +/- 2 degrees from idle to peak revs, so yes, you do have a problem - excess end play, worn, wobbly breaker plate or worn bushings are the places to start.

Distributor "blueprint overhauls" have been discussed many times.

Duke

[Larry S.]

Re: Distributor Dwell....

Thanks Duke, looks like I pull the distributor !
Larry

[Larry S.]

Re: Distributor Dwell....

Duke,
I also was wondering that if the points-set had a weak spring, would that cause the dwell to drop say 3+ degrees from idle to say 2500 rpm? I havent replaced the points yet.

[Duke W.]

Re: Distributor Dwell....

I doubt it. The OE 19-23 oz. points should hold within two degrees to at least 5500, and I recommend the 28-32 oz. points for engines with redlines over 5500.

I bet your distributor has never had a major overhaul, so it's about time. When you pull the upper grease well seal about all you will probably see is "dust", which are the remants of the original grease.

Duke

[Larry S.]

Re: Distributor Dwell....

Thanks Duke.