Rust in distributor cap?

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Oct 25, 2018 | 11:54 AM

Sayfoo

Thread Starter

Safety Car

Joined: Sep 2005

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From: Orange County Ca

Rust in distributor cap?

While tracking down a rough idle and random misfires, I discovered what appears to be a dry rust coating inside my distributor cap. It's a even coat over the whole inside. Cleaning it off helped a lot, so I'm assuming that it is conductive.
So, the question is, where's it coming from? And, is it actually rust?
Everything inside the dist. looks clean and dry. No apparent rust anywhere.

Oct 25, 2018 | 02:41 PM

Haggisbash

Melting Slicks

Joined: Oct 2012

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From: Dunedin NZ.

This is my theory, many of the ferrous metal components in the distributor are uncoated steel so combine any humidity and a little moisture and you will get rust, the shaft and other components are spinning at 1/2 engine speed so the rust is flung onto the inside of the cap. To exacerbate the problem you have high voltage sparks jumping between the rotor and the plug lead terminal posts, this sparking generates Ozone which is corrosive so this increases the rusting. You can spray the metal components sparingly with WD40 or the like occasionally to minimise the issue. This corrosion has been found to cause a lot of failures of the Optispark ignition system on 350 engines in the C4 Vettes, In fact on the last the last couple of years of production of the C4 the distributor was fitted with a manifold vacuum ventilation system to get rid of the Ozone and prevent the failures.

Oct 25, 2018 | 03:15 PM

lars

Tech Contributor

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From: At my Bar drinking and wrenching in Lafayette Colorado

Jeff Smith has a good write-up on the subject here:

https://www.onallcylinders.com/2016/...ou-avoid-them/

Lars

Oct 25, 2018 | 08:23 PM

Sayfoo

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Safety Car

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From: Orange County Ca

OK 2 great answers. My cap looks just like the picture in Jeff's blog. Thank you.
I have a stock, points type dist., with high quality (Napa) cap with copper terminals and rotor. That end looks good. I think I'll start by checking the resistance of the plug wires.

Last edited by Sayfoo; Oct 25, 2018 at 08:26 PM.

Oct 26, 2018 | 01:58 PM

MelWff

Race Director

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Have you removed the rotor and looked at the weights and springs?

Oct 26, 2018 | 02:01 PM

lars

Tech Contributor

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From: At my Bar drinking and wrenching in Lafayette Colorado

That's the area that the iron oxide gets transferred from. You most likely have some rust on the springs and on the weights and weight hinge pins. Clean it up and lightly lubricate the friction surfaces.

Lars

Oct 27, 2018 | 03:25 PM

Sayfoo

Thread Starter

Safety Car

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From: Orange County Ca

The springs and weights look clean. There is some wear on the raised button on the plate that the weights that rub on. I have in the past, resisted lubing these or the weight posts because I didn't want to get them gummed up and also fling oil around the inside of the cap. But, they are fairly loose, so I'll give them a shot.

Last edited by Sayfoo; Oct 27, 2018 at 04:43 PM.

Oct 27, 2018 | 06:53 PM

HeadsU.P.

Le Mans Master

Joined: Aug 2017

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From: Cool Northern Michigan

White Lithium (sp?) Grease. Red & white spray can w/straw, at Walmart.
It can take the heat & won't fling off the dizzy wts.

Can also be used on door hinges, hood hinges, hood latching cables, door latches, etc. Its the "clean grease".