Ozone in the distributer cap.

[Circlotron]

You could put one of those old school emission one way check valves in the vac line so no fuel vapour gets inside the distributor cap. Maybe also a small plastic fuel filter to stop dirt being drawn into the vacuum line to the manifold.

[peejay]

How about four pickup coils and make a distributor driven waste spark DIS ignition?

The fun part is you can leave the distributor cap on there with no wires on it and watch people's heads explode.

I did this years back on a 12A Mazda. I also saw someone do this with a 907 engined Lotus Europa, and the owner told me that he bought the ignition set up as a kit! So the way I see it. there is NO EXCUSE for bolt in DIS systems for common V8 engines to not exist. All you really need is a "breaker plate" with four pickup coils on it.

[midnightbluS10]

Might want to take a read through this. They bring up soon good points about MSD caps and corrosion, surface treatments, etc... Like the formation of nitric acid inside the cap contributing to the corrosion. I've never even heard that before.


https://chme.nmsu.edu/available-analysi ... butor-cap/


https://chme.nmsu.edu/files/2015/02/CHM ... RTovar.pdf

[oldhead]

GM LT1 engines used a vacuum port to draw air from a fitting in the intake duct through the front-mounted distributor to vent the cap. A local police force converted some to propane. Bad move; a gas accumulation in the intake was drawn through the distributor in one vehicle, resulting in an explosion and the bomb squad being called in...

Some later engines had a fan on the distributor shaft to dissipate ozone.

I like this story. A good one for an engineering prof to have at hand as well.

It is impossible to make anything foolproof, because fools are so ingenious.

My 1995 lt1 Has 2 check valves in the dist vacuum line stock

[ProPower engines]

[/quote]My 1995 lt1 Has 2 check valves in the dist vacuum line stock
[/quote]

1 is a vacuum retard check valve and the other is to limit vacuum for advance speed.
But that said the MSD system has had this issue since they were invented.Some dist.'s are better then others at venting the burnt gas inside the cap then others.

If the vacuum line is put in the air filter some where that will drag enough vacuum to keep the cap clean and deposit free without the worry of gas vapors entering the cap.
Unless the vacuum is from a ported source in the intake or carb there is no chance of vapors collecting in the cap.
The marine industry has been doing that very same thing for 30 years and if anyone would have cause for concern it would be a boat owner. The vacuum line has been attached to the top side of the flame arrestor for ever and no issues.

If you put an bulkhead style fitting in the air filter base that will allow the air drawn past it to create enough of a vacuum signal to draw the burnt air out keeping the cap clean.
as I mentioned before there has to be a air inlet capable of allowing as much air into the dist. body as the vacuum source the vacuum source can draw out of the dist. body.

Marine ignition systems have to be in the worst environment for corrosion build up and with todays factory installed ignition systems they produce the same unwanted affects as far as the cap contacts are concerned and they fixed it with a simple vacuum port and hose and a very little vacuum amount as it did not need any more then that.
We do it to every engine and since we started doing it it was done wonders to greatly extend the cap life on drop in and external box powered MSD and other ignition systems.

The key here is to create a swirl of incoming air into the cap. put the vent on the side opposite the screen vent the manufacture put into it. With the vent in the cap and the vent in the bottom this will draw fresh air into the area surrounding area of the contacts which is all thats needed. No reason to over think this just copy a system that had had a few million dollars spent in testing and has CSA approval for marine use where insurance can be voided or denied if the wrong un-approved ignition system is used and a claim arises.

[peejay]

My 1995 lt1 Has 2 check valves in the dist vacuum line stock
[/quote]

1 is a vacuum retard check valve and the other is to limit vacuum for advance speed.[/quote]

Huh? There is no mechanical or vacuum advance in the LT1 distibutor. Just an optical crank positon sensor (thus the name Opti-Spark)

GM put breathers in the distributor cap to prevent moisture from collecting in it. It's mounted horizontally (well, vertically) behind the water pump and if any moisture gets in there it quickly leads to a misfire on the "bottom" cylinders.

[user-23911]

Sounds like there's too much gap between the rotor arm and the distributor cap. Not only does the gap make ozone but it also reduces the energy to the sparkplugs.

Fixing the problem at source makes more sense than trying to fix the effect of the problem.

[midnightbluS10]

My 1995 lt1 Has 2 check valves in the dist vacuum line stock

1 is a vacuum retard check valve and the other is to limit vacuum for advance speed.

Huh? There is no mechanical or vacuum advance in the LT1 distibutor. Just an optical crank positon sensor (thus the name Opti-Spark)

GM put breathers in the distributor cap to prevent moisture from collecting in it. It's mounted horizontally (well, vertically) behind the water pump and if any moisture gets in there it quickly leads to a misfire on the "bottom" cylinders.

Well they definitely exist. <shrug> I'd be willing to bet that the formation of nitric acid in the cap contributes to some issues, also. How much? Who knows without testing.


Fixed the screwed up quotes, also.

[pamotorman]

AMC had problems with gasoline vapors getting into the dist thru a leaking vacuum advance and having a explosion blowing off the cap. GM put a vertical loop in the vacuum advance line to keep gasoline out of the vacuum advance.

[dwilliams]

The rotor-to-contact gap determines the minimum voltage needed to jump the gap. One trick back in the day was to shorten the rotor to increase the voltage at the plug. (secondary-gap plugs and those JC Whitney "spark boosters" that spliced into the plug wiresworked the same way)

The rise and discharge times of a traditional battery-and-coil were fixed. But modern electronic ignition systems have much faster rise times, and their voltage isn't necessarily limited by what the coil produces.

Given that, you might be able to close up the rotor to contact gap to reduce arcing in the cap. And it's still worthwhile to Dremel a window into an old cap of the same brand to watch the rotor alignment with a timing light.

Also note that piston-engine aircraft that have onboard compressed air usually meter some to the cap to flush ozone out. Most cars don't have a convenient source of compressed air, but if you have a blower or turbo, you have a source when you really need it.

[pamotorman]

GM came out with a emission rotor with a shorter tip to build up the energy it took to jump the plug gap. the rotor tip had a "E" stamped on it. it did not work well for high RPM engine. when i was doing HEI for racing i made a fixture that located off of center hole in the cap to bend the cap contacts closer to the rotor tip.

[af2]

On the distributer I run when I went to crank trigger I gutted the 80's-90's electronics and now have a big window. Same cap and rotor for 12 years and many more..

[groberts101]

I've seen a decent amount of poorly indexed rotors cause issues that normally don't exist in a vented cap too. Even a lot of "pro's" who don't ever check before tossing parts at the problem.

[ProPower engines]

My 1995 lt1 Has 2 check valves in the dist vacuum line stock

1 is a vacuum retard check valve and the other is to limit vacuum for advance speed.[/quote]

Huh? There is no mechanical or vacuum advance in the LT1 distibutor. Just an optical crank positon sensor (thus the name Opti-Spark)

GM put breathers in the distributor cap to prevent moisture from collecting in it. It's mounted horizontally (well, vertically) behind the water pump and if any moisture gets in there it quickly leads to a misfire on the "bottom" cylinders.
[/quote]

I think the OP was talking about ford distributors.
I have seen lots of the later ford stuff that still has advance mechanisms in the dist. with a check valve in both the adv. and the retard port.
.I was referring to a ford dist. as some used 2 check valves. You are right the opti spark dist don't use them for that
My bad I miss read

[Circlotron]

Suzuki LJ80 4WD had a vented distributor cap. Maybe mostly for moisture removal though.