Posting a link to a few of the related pictures that evaporated due to the Photobucket thing.

https://www.plymouthcarclub.com/2018/05 ... -cap-gaps/

Any other requests for additional specific pictures will be found at that same link.

Don

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1965 Dart 125k, 225, Carter BBD Super Six, 2 1/4 single exhaust., sbp manual scare-bird front disc, 7 1/4 rear 2.94 sure grip, 15 x 4.5 wheels, 833 OD with hyd. throw-out bearing, electric fan, ram air/heated air, Accusump.

My old ignition scope is currently buried, I have a sm
Snap on "counselor" I picked up via CL probably 10 years ago.
(I liked the old sun 1015 and 1215 I used at past jobs better but this one does the job)
I wonder if it could be picked up on a scope screen if this we're an issue?
I've forgotten a thing or 2 about scope patterns over the years

The Sun 1215 that I used did a great job at displaying on the scope the entire cycle showing voltage in the coil line.
I'll dig out the picture and add it to the link that shows some past pictures. It even shows the impact of opening up spark plug gaps for example.

Don

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1965 Dart 125k, 225, Carter BBD Super Six, 2 1/4 single exhaust., sbp manual scare-bird front disc, 7 1/4 rear 2.94 sure grip, 15 x 4.5 wheels, 833 OD with hyd. throw-out bearing, electric fan, ram air/heated air, Accusump.

Thank You Reed for bringing the images into this thread.... as I am about to give this a go with a points distributor that I just acquired... Tho I am not sure I can drill the required holes in the distributor bottom/side with out drill press? Might try it with a cutoff wheel on the angle grinder...

Unless you have a spare distributor that you can make into a jig to measure gaps between the rotor tip & new cap terminals you are shooting in the dark making up your own rotor tips. I test every rotor/cap before installation and grind the offending cap terminals each time I'm changing the cap & rotor. Essentially they become a matched set. Without the jig you cannot do that important step. I have been setting the rotor tip to cap terminal to within .015 to .025 inch as a working guide and checking resulting plug wire voltage to validate my Dart remains reliable.

Don

ps: I go to mid Vt. during the summer months.

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1965 Dart 125k, 225, Carter BBD Super Six, 2 1/4 single exhaust., sbp manual scare-bird front disc, 7 1/4 rear 2.94 sure grip, 15 x 4.5 wheels, 833 OD with hyd. throw-out bearing, electric fan, ram air/heated air, Accusump.

Thanks Don for sharing and documenting your thinking on this.
Yes I have just gotten a spare distributor to modify into a testing and setup jig/distributor.

When you are needing to increase clearance, how do you grind the terminals?

("When you are needing to increase clearance, how do you grind the terminals?").

A large diameter wheel on a Dremel is used to shape the terminal to the same radius as the other terminals.

Extending your thinking; "What to do if the clearance is greater than .025??" I have seen as much as .100" with standard rotors sold at NAPA.

I buy the NAPA MO3000 extended rotor which is .060" longer and use distributor caps made in the 60's & early 70's as a starting point.

Why worry about a .100" gap? Think of the sparking occurring in the distributor cap with .100" gaps and then measure the coil line voltage. Don't be surprised if the wide gap gives you readings well above 10,000 volts. Also don't be surprised that cap breakdown & coil breakdown is fast. Those with an ECU will also see poor reliability.

Bottomline is .025" clearance is a max that gives the coil wire Voltages around 6000V and reasonable reliability. .015" clearance as a minimum allows for distributors with bushings with only slight wear. If you have trouble findings new bushings for your distributor to hone know that Mopar flatheads all the way back to 1933 use the same bushings so your sweep for boxed bushings available for your slant is large. If you need instructions on how to remove, install, and machine distributor bushings for your slant I might be still able to find them from a couple of decades ago

Don

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1965 Dart 125k, 225, Carter BBD Super Six, 2 1/4 single exhaust., sbp manual scare-bird front disc, 7 1/4 rear 2.94 sure grip, 15 x 4.5 wheels, 833 OD with hyd. throw-out bearing, electric fan, ram air/heated air, Accusump.

I will aim for .015, and see how things go. The spare distributor is in great shape, but I will have to check the results on electronic distributor as well, It might have more play in the bushings. I have a flathead as well, and find that parts availability is almost better for them than it is for the slant 6.

Your goal is to avoid:
1) having the rotor contact the cap terminals when spun up & changing speeds (resulting in breaking distributor drive gear)
2) excessive coil line voltage

So staying within a do-able range on rotor clearances during all conditions as a goal

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1965 Dart 125k, 225, Carter BBD Super Six, 2 1/4 single exhaust., sbp manual scare-bird front disc, 7 1/4 rear 2.94 sure grip, 15 x 4.5 wheels, 833 OD with hyd. throw-out bearing, electric fan, ram air/heated air, Accusump.