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Allis Chalmers Discussion Forum
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setting points - erroneous dwell angle

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Rock_Picker(MO)

03-26-2008 20:58:59




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I"m trying to use a dwell meter to properly adjust the ignigion points on an old muscle car. The feeler gauge setting compared to the dwell angle reading is way off (0.014" equals approximately 20 degrees -- 0.014" should equal approximately 32 degrees) {I know my meter is good, all electrical connections [grounds,etc] are good}. Could an improper size condensor be causing the problem?




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Rock_Picker(MO)

03-28-2008 18:39:14




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 Re: setting points - erroneous dwell angle in reply to Rock_Picker(MO), 03-26-2008 20:58:59  
I think I got it figured out. The shaft end play is about .070" (far in excess of the specs). I picked up another (used) distributor today that meets all shop manual specs. If that doesn't solve the problem, I'm gonna follow Brian's advice and go to an upgraded ignition system..... ..... tx for all the comments.....RP



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ABC Calif

03-27-2008 15:52:01




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 Re: setting points - erroneous dwell angle in reply to Rock_Picker(MO), 03-26-2008 20:58:59  
The Only Way That You Can Get The Dwell AND The Point Gap To Factory Spec's Is To Bend The Point Contact Arm. That Is The Arm That Pivots, If You Bend That Arm Away From The Distributor Shaft That Will Increase The Gap Without Changing The Dwell.



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Brother Dave

03-27-2008 06:13:05




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 Re: setting points - erroneous dwell angle in reply to Rock_Picker(MO), 03-26-2008 20:58:59  
If the shaft side to side play is at the top of the spec of .003 that alone could cause a 6 degree change in the dwell angle. The other two degrees could be in the error of the "feel" of the feeler gauge. Trust the dwell angle meter especially if the shaft bearings are slightly worn. This would not be uncommon on a shaft and bearing assembly of that vintage.



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Rock_Picker(MO)

03-27-2008 05:32:51




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 Re: setting points - erroneous dwell angle in reply to Rock_Picker(MO), 03-26-2008 20:58:59  
P.S. I have three dwell meters and they all read the same when connected to the engine.



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Rock_Picker(MO)

03-27-2008 05:30:21




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 Re: setting points - erroneous dwell angle in reply to Rock_Picker(MO), 03-26-2008 20:58:59  
The engine is a 1969 Dodge 440 cid, 8 cylinder, single points type distributor. The factory specs call for:
1) Contact Gap: .014" to .019"
2) Dwell Angle: 28 to 33 degrees
3) Shaft Side Play(New or Rebuilt): .000" to .003"
4) Shaft End Play(After Assembly) .003" to .017"

The factory shop manual gives a procedure for checking change in dwell with change in engine speed....I can't tell there is an appreciable change.

I don't have a good way to check distributor shaft side play..... will tinker with it some more.

Thanks to everyone for the input..... .If there are other suggestions, I would appreciate hearing them. I'll keep tinkering with it..... ...RP

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Joe(TX)

03-27-2008 04:40:11




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 Re: setting points - erroneous dwell angle in reply to Rock_Picker(MO), 03-26-2008 20:58:59  
Rely on the dwell meter. the feller gauges will just get you close, on used points especialy.



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Joe(TX)

03-27-2008 04:40:06




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 Re: setting points - erroneous dwell angle in reply to Rock_Picker(MO), 03-26-2008 20:58:59  
Rely on the dwell meter. the feller gauges will just get you close, on used points especialy.



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Gordon in IN

03-27-2008 03:02:25




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 Re: setting points - erroneous dwell angle in reply to Rock_Picker(MO), 03-26-2008 20:58:59  
Might be worn distributor shaft bearings. Does the dwell change or "surge" with slight changes in engine speeds? Will distributor shaft move from side to side with firm "finger pressure"? Just something I have had problems with in the past. Good luck, Gordon in IN



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Bob

03-26-2008 21:30:21




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 Re: setting points - erroneous dwell angle in reply to Rock_Picker(MO), 03-26-2008 20:58:59  
1. What are you working on?

2. What are the factory "specs" for point gap and dwell? .014" and 32�?

3. How do you KNOW your meter is "in calibration"?

4. Unless the condensor is out of spec by an "exponential" amount, I can't see it affecting the dwell reading appreciably.



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Brian Jasper co. Ia

03-28-2008 04:51:55




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 Re: setting points - erroneous dwell angle in reply to Bob, 03-26-2008 21:30:21  
I don"t know for sure on big block Chrysler, but on small blocks they have a bushing in the block that the distributor/oil pump drive gear runs in. They like to wear and in turn severely wear the distributor shaft. Unless this is a very nice original car, dump the point distributor for a Mallory Unilite. No points and much hotter more reliable spark.



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