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Front Mount Ignition Issues

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nondem

04-29-2008 17:50:56




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This is an early 1950 8n - Front mount. With a round coil conversion(original square coil gutted)

I just got new points/cap/rotor in with the last batch of parts. The cap doesn't fit as perfectly as the old one but it does fit and allow all the latches to work and the rotor to move freely.
I've not put the distributor back on the tractor yet but I attempted to bench-test it by connecting an Ohmeter to the caps high-tension input(where the springy-thingy touches) and each of the 4 cap outputs while turning the distributor shaft.

In theory I should get a connection to each of the 4 outputs on each revolution. I'm not...I'm trying to figure out if that means there is a problem - or that there is not enough voltage to bridge the gap between the rotor-prog and each output contact. Is there supposed to be physical contact between the rotor and cap contacts as it goes around?
I tried the same experiment with the old cap and got no contact either.

On another note - just to confirm what I "think" I know:

The distributor will only mount on the engine without having to force-it if the rotor is in the right position for wherever the engine is in it's rotation.

Is this true?

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corvette8n

04-30-2008 10:11:55




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 Re: Front Mount Ignition Issues in reply to nondem, 04-29-2008 17:50:56  
I just went through this exercise, new square coil but pigtail was bent off the the side so I had no spark when put back together. I took dist. off again and bent the pigtail so it fit in the screw slot. I then put 6 volts to the top of coil using a batt. charger and placed a timing light, in one of the cap openings and grounded the other side, I them spun the back of the dist. with my hand and I had spark. Bolted everthing back on the tractor, hooked up coil wire turned key and it started within have a spin. Ran it for an hour and a half, not one miss.

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nondem

04-30-2008 04:50:18




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 Re: Front Mount Ignition Issues in reply to JohnIa, 04-29-2008 17:50:56  
Oh, and the original cap shows indication that the rotor prong had made contact with some of the contacts.



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souNdguy

04-30-2008 06:26:18




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 Re: Front Mount Ignition Issues in reply to nondem, 04-30-2008 04:50:18  
Either ill-fitting cap, or bad manufacturing.. or a loose rotor button.. or bad distribuitor shaft bushings.

All of these can allow the rotor button to contact the cap contacts.

soundguy



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nondem

04-30-2008 04:48:57




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 Re: Front Mount Ignition Issues in reply to old, 04-29-2008 17:50:56  
In defense of my own ignorance - the industry had largely moved to solid-state ignition types before I was 10 years old...This is hella-retro for me.



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souNdguy

04-30-2008 06:24:39




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 Re: Front Mount Ignition Issues in reply to nondem, 04-30-2008 04:48:57  
Solid state or points.. it don't matter... if it uses a distribuitor design.. there is a micro air gap between the rotor and the cap contacts. Now.. COP ( coil on plug ) designs get away from this.

Soundguy



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souNdguy

04-30-2008 04:46:49




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 Re: Front Mount Ignition Issues in reply to nondem, 04-29-2008 17:50:56  
Nondem.. I agree with bruce and the others... bad theory ( go back to electronics school ) (wink)

Also.. when refering to a spring contact on a square coil.. specify flat high tension spring ( high voltage ).. or the pigtail low voltage spring.

The flat tab spring is what passes KV to the cap, to the rotor, to the spark plugs.. all thru a couple air gaps ( cap to rotor and plug gap )... thus no continuity..

soundguy

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Den N Ms

04-29-2008 19:34:46




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 Re: Front Mount Ignition Issues in reply to nondem, 04-29-2008 17:50:56  
nondem,To check it for shorts and continuity place one lead on the big screw that the spring on the coil sets on ,and the other to the distributor case.Turn the shaft and you will see on the meter when the points open and close.



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Den N Ms

04-29-2008 19:27:28




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 Re: Front Mount Ignition Issues in reply to nondem, 04-29-2008 17:50:56  
nondem,The rotor should have a gap of .006-.008 between the end of the rotor tang and the inside termanals of the cap that the spark will jump across.



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Dunk

04-29-2008 18:06:56




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 Re: Front Mount Ignition Issues in reply to old-9, 04-29-2008 17:50:56  

TennesseeMan said: (quoted from post at 22:03:20 04/29/08) Just like a spark plug their is a space and the spark is gonna jump. There is actually no metal to metal contact between the rotor and the inside of the cap where the four contacts are. If this I what I'm understanding from the question you asked.


TennesseeMan is right!!

Forgit your meter, and the high tension stuff, it WON'T work!!!

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Bruce (VA)

04-29-2008 18:06:23




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 Re: Front Mount Ignition Issues in reply to nondem, 04-29-2008 17:50:56  
"In theory I should get a connection to each of the 4 outputs on each revolution."

Nope. Bad theory. The rotor tip does not contact the plug leads of the cap. Like horseshoes & hand grenades, close counts. If you get the cap mis-aligned, and the tip of the rotor touches it, the rotor breaks.

Use the ohmmeter to see if your points open & close. Check that the lead from the coil is not grounded. You can make sure the top of the rotor is touching the center of the cap by checking continuity between the little metal tab on the cap & the end of the rotor.

Look at the end of the crankshaft when the distributor is off. Which way is the slot pointing? Up & down? 1 & 7 o'clock? Whatever....twist the distributor shaft accordingly. Then, put it back on the tractor.

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36 coupe

04-30-2008 02:36:34




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 Re: Front Mount Ignition Issues in reply to Bruce (VA), 04-29-2008 18:06:23  
I cant help laughing at some posts I see.Rotor wouldnt last long touching the contacts.This does happen with some import caps.One of the better ones are boobies who try to measure ignition voltage with digital meters.



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CENTAUR

04-29-2008 18:05:43




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 Re: Front Mount Ignition Issues in reply to nondem, 04-29-2008 17:50:56  
There should not be contact between the rotor and cap as the voltage will bridge this gap.The tang is as you see off center so you cannot mount the wrong way. CENTAUR



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TennesseeMan

04-29-2008 18:03:20




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 Re: Front Mount Ignition Issues in reply to nondem, 04-29-2008 17:50:56  
Just like a spark plug their is a space and the spark is gonna jump. There is actually no metal to metal contact between the rotor and the inside of the cap where the four contacts are. If this I what I'm understanding from the question you asked.



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