Slant Six Forum
https://slantsix.org/forum/

Distributor Cap Terminal To Rotor Clearance
https://slantsix.org/forum/viewtopic.php?t=60552		 Page 7 of 7
Author:  DonPal [ Thu Jun 08, 2023 7:37 am ]
Post subject:  Re: Distributor Cap Terminal To Rotor Clearance
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
Author:  volaredon [ Thu Jun 08, 2023 4:40 pm ]
Post subject:  Re: Distributor Cap Terminal To Rotor Clearance
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
Author:  DonPal [ Thu Jun 08, 2023 7:47 pm ]
Post subject:  Re: Distributor Cap Terminal To Rotor Clearance
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
Author:  Jase [ Sat Feb 28, 2026 6:08 am ]
Post subject:  Re: Easier Rotor Made Using SlantSixDan Other Tip Suggestion
Quote:
Quote:

Below picture steps involve:
1) comparing MO3000 tip to FD117

Image

2) marking FD117 tip for cutting

Image

3) center punching FD117 tip for drilling

Image

4) trial fitting modified FD117 tip in MO3000 rotor

Image

5) using soldering iron to flow MO3000 rotor plastic into FD117 grooves

Image

Image

6) marking distributor gear to use as indicator for when machining distributor cap gaps

Image

I can provide more detail on each little part of the machining if there is an interest.
YES, PLEASE!
Quote:
The Cap:
Next step is to try machining a poor cap with excess eccentricity into a decent one to fit the above rotor (which is about .010 longer than a standard MO3000 rotor tip). The idea is to do it without a jig as most might attempt. Then check it with the jig to see how good it actually turned out.
You are doing some very great work here, Don. Thank you for doing it and thank you more for documenting and sharing it. I look forward to seeing your work on the caps!
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...
Author:  DonPal [ Sat Feb 28, 2026 7:46 am ]
Post subject:  Re: Distributor Cap Terminal To Rotor Clearance
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.
Author:  Jase [ Tue Mar 03, 2026 4:10 am ]
Post subject:  Re: Distributor Cap Terminal To Rotor Clearance
Quote:
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.
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?
Author:  DonPal [ Tue Mar 03, 2026 8:20 am ]
Post subject:  Re: Distributor Cap Terminal To Rotor Clearance
("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
Author:  Jase [ Wed Mar 04, 2026 4:19 am ]
Post subject:  Re: Distributor Cap Terminal To Rotor Clearance
Quote:
("When you are needing to increase clearance, how do you grind the terminals?").

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
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.
Author:  DonPal [ Wed Mar 04, 2026 7:26 am ]
Post subject:  Re: Distributor Cap Terminal To Rotor Clearance
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
Page 7 of 7 All times are UTC-07:00
Powered by phpBB® Forum Software © phpBB Limited
https://www.phpbb.com/