Automotice distributor cap, rotor corrosion

[themess]

If this would fit better somewhere else, please say so.

1995 Mazda Protege, 226K miles, 1.5 liter in-line 4 cylinder engine.

I had the car for 45K miles. Has generally been very reliable and economical. First the photos:









Rotor, cap, attachment for cap (end of camshaft, I think) were all bright and shiny less than 3K miles ago. This is the fourth set of cap and rotor that has corroded, and it is happening quicker. The first time I racked it up to a long time between tune-ups. The second, to antifreeze getting inside when the cooling system was being purged of air with the radiator cap off. Green corrosion is visible, making me suspect infiltration of something. The last two times might be due to crud entering, either between the cap and distributor, or due to a faulty seal in the distributor. Various colored flecks are visible in the photos.

Systems with breaker points need a condensor to prevent arcing and buring of the points. Does breakerless ignition need something similar?

Any ideas on what to check? The Mazda distributor cap gasket will definitely be replaced.

Mazda prices are absurd. Rotor and distributor cap run about $35! Cap gasket is $12.

[koolaid_kid]

Tom, this really should go in the "Other Project" section, but I will answer you. You have a hairline fracture somewhere and it is getting worse. I would replace the entire distributor and be done with it. It is $164 at CarPartsWarehouse: distributor

[TooManyToys]

Not familiar with this vehicle but ...... Your right that most likely gases are coming up through the distributor shaft area and condensate in the cap. Distributor seals can be a factor. But if there is enough pressure within the block to allow this it's more likely that the PCV or other vent plumbing is obstructed. Normal blow-by past the rings has to go somewhere. Even with seals compromised there should be enough draw vacuum into the intake to take care of this.

[koolaid_kid]

Well, if the seals of the shaft were leaking, it would be oily there, since the distributor fits on the end of the camshaft. However, it is rusty, not oily.
That particular distributor has a base that is part dielectric plastic and part base metal. Somewhere on the exterior is a crack, which is letting atmospheric air in.

[TooManyToys]

kk, Didn't mean to dismiss the crack. I wrote the message before I saw yours and my reference to seal was meant to be any loss of integrity.

[koolaid_kid]

I understand, and not a problem. And I agree, I went there as well. I just looked around at the design of the distributor, and decided if it did leak it would be oil. As always, I reserve the right to be incorrect, it does happen to all of us, time to time.

[Crankthat]

When you replace smear some Vaseline or a non conductive grease between the distributor and cap to insure not getting past there.
Do not be afraid to go thick where the two halves join up.

[TooManyToys]

I've seen this issue with old 289 Ford motors. As mentioned, bad motor evac or excessive blowby, so my viewpoint. Not sure how that much condensation would manifest itself there.

[koolaid_kid]

I've seen this issue with old 289 Ford motors. As mentioned, bad motor evac or excessive blowby, so my viewpoint. Not sure how that much condensation would manifest itself there.

Not through the path you suggest at any rate. 289 engines were pre-emission engines, so no safeguards were in place for blowby control.
You may be correct, but only continued parts replacement will find out for certain.
Best of luck, Tom.

[rustybronco]

A lot of times there will be a secondary plastic cover that sits over the points and condenser (pickup/ hall effect) to keep out the moisture and dust, then the distributor cap fits over it and the distributor housing. Check to see if is supposed to have one or not.

Plus there's probably an o-ring used to seal the distributor cap to the housing as well.

Similar to this... http://contentinfo.autozone.com/znet.../F800/image/4/

Systems with breaker points need a condensor to prevent arcing and buring of the points. Does breakerless ignition need something similar?

No. A capacitor is usually required for noise suppression only.

[TooManyToys]

289's had PCV.

[themess]

Thanks for the insightful replies. Next time I need help on an automotive problem, I'll try the other forum, and see how many people respond.

The rust means that water is getting inside the distributor cap. Mazda uses a fancy gasket between this horizontal distributor and its cap. It tears easily. I'm spending $15 on a replacement. I'll clean up every thing as carefully as I can, re-using the same parts. After a thousand miles or so, I'll look inside. If crud is still entering, I'll spend the $200 on a replacement distributor.

[rustybronco]

Look into seeing if it uses the plastic cover.

[themess]

Look into seeing if it uses the plastic cover.

Does not. Complex gasket between cap and base. O-ring seals base to cylinder head.

[themess]

status

Not having used a timing light for 30 years, it took a while to find. So far, I haven't been able to locate the timing marks on the engine either. So I put it back together with a new gasket, or gasket plus plastic cap, referred to two messages above.



The distributor cap cleaned up nicely, but the rotor was too badly corroded to reuse. I put dielectric grease between the rotor and the distributor shaft, to inhibit corrosion. The car has been running well for several days. I'll pull the cap in a thousand miles or so to see how it looks. If any significant amount of crud is getting inside, I'll find a different distributor.

Thanks again for the help.