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Topic: Arching Rotor / Distributor Cap (Read 4744 times) previous topic - next topic

Arching Rotor / Distributor Cap

1984 Cougar, 3.8L, TBI

About every 1000 miles I have to go in and remove the builtup (grey crust) from the distributor rotor and cap pins.

Since after market stopped making the multi-point rotor this has been a problem for about 10 years.  Maybe getting old, but starting to $#$%^ me off.

Anyone have a solution. Example:

1)  Will grinding an indentation in the rotor spad stop the arcing
    and replicate the multi-point rotor?
2)  Will a new coil help (1984 original)?
3)  Any substitute (rotor or distributor) or solution that works?


Thanks
David

Arching Rotor / Distributor Cap

Reply #1 –
Part of the crust buildup is due to different materials and is most pr0nounced when aluminum is used in both the rotor tip and cap terminals. Aluminum is the worst and is a poor conductor compared to copper, brass and bronze.

I doubt that your coil is at fault, however it never hurts to take a DVM to it and check that the resistances are correct and that the secondary coil windings are not shorted to ground. Checking your coil and plug wire resistance wouldn't hurt either.

Have you tried a very light coating of dielectric grease (same stuff you use for spark plug boots) on the tip of the rotor (no dielectric grease on the edge nearest the the cap terminals)? I have done this on many vehicles as a matter of routine (it is directly called for by some applications & manufacturers - like the '86 Escort I used to own) and as a fix for what you describe. I have had pretty good success in increasing the life of the cap & rotor with this approach. Build up will happen always with aluminum cap terminals but the dielectric will slow it down in most cases.

As for cap and rotor suggestions, avoid aluminum on both the rotor and cap. You may try something like these (with the dielectric grease - links below are for push on type rotor, bolt on rotor type is available):


Push on Rotor:
Rotor
Cap

Bolt on Rotor:
Rotor
Cap
*** note the absence of aluminum components, components are brass, bronze, tungston and stainless. Parts are illustrative and not an endorsp00get of the specific product/manufacturer/retailer***

I hope this helps!

Michael

Arching Rotor / Distributor Cap

Reply #2 –
Thanks for response Michael.

Yes -- am using dielectric grease.  In fact, initially I thought it was the dielectric grease that was hard at the end of the rotor.  Also using brass terminals (Cap and Rotor are Standard).

In spending this evening searching the net, find my problem is a common car problem, but no real solutions to date. 

From my research -- for whatever its worth -- and hopefully those posting know what they're talking about:

1) It appears the electrical process (spark jumping) creates certain gases which cause most of the gray crusting. 
2)  These gases need to be vented.
    (In my case I'm using a vented cap.  Some distributors, such as  certain GM's also have vents on bottom.  Whether Cougar does I'll check tomorrow but my distributor is rebuilt and about 1 year old so no bottom vents -- if exist -- should be clogged.)
3)  Type of contacts (aluminum, versus brass) supposedly make no difference.  Sorry to burst your bubble.  Supposedly Niehoff did a test using caps with several different metal terminals in each cap and found no difference.

--------------
Per my 84 shop manual, Ford recommended multi-point rotor but if using blade must use dielectric grease.  This is why I'm using it.

Next attempt is to try and rework an old rotor.
Thoughts are to either  see if I can somehow make it multi-point
or take the spade tip and grind it down to a single point.
Hopefully single point won't Screw something up!!!!!!!


-----------------------
Any other suggestions, beside your initial post Michael greatly appreciated.

Arching Rotor / Distributor Cap

Reply #3 –
No bubble burst here... I should have included a statement that the cap terminals and rotor will degrade over time, regardless of the material used. You are correct, and I should have included, that the crust is caused by out gassing due to to the arcing. I apologize for any misunderstanding that may have resulted from my ommission(s).

On the topic of materials used, I am unfamiliar with the testing you refer to. I can only speak from the point of training and experience, both as a previously licensed mechanic (changed careers) through personal research and product use in 12v automobile systems and 120/240v residential systems.

That said, I got tired of my MSD Blaster TFI Coil shredding my cap and rotor every 5,000 miles or so (both aluminum and brass types, with and with out dielectric grease) even with Accell stainless, spiral wound, solid core plug wires. So I looked around for a more suitable cap and rotor. I found it in the form of the MSD Ford HEI Cap. The choice was based less on the cap being MSD but more on basic electrical properties in relation to conductors. This particular cap and rotor use brass, stainless, bronze, etc. (much like I posted above). The difference from standard caps? Larger terminals inside the cap. Just as in wire size, the larger terminal presented less resistance thus less heat generated thus less out gassing thus slower degradation of the cap and rotor. I have had this cap installed for about 30,000 miles and have cleaned the carbon on the terminals and edge of rotor tip maybe once (would have been between 10-15k miles). No Gray stuff at all, just checked prior to responding (no dielectric grease was ever applied). The cap is vented and I do use the factory rubber boot. The quality of the brass used would also be a big factor.

As I think about it though, another factor comes to mind; the air gap between the rotor tip and cap terminal. As the gap gets larger, resistance goes up as does heat generated, amount of out gassing, etcetera. Some manufacturers may use the same rotor for multiple applications with different caps which could introduce changes in the air gap from application to application depending on the actual parts used. A smaller air gap may also be part of the MSD Cap and rotor design.

Maybe you can find a rotor and cap combination that uses brass (aluminum is proven to be a poor conductor) and provides the smallest operational air gap possible and see how that works out. Also, I wouldn't modify the rotor tip too much as your dwell (although set by a microprocessor it may not be able to arc off the rotor tip in the correct spot), along with the air gap, will be negatively affected if too much material is taken off. As to how much modification of the rotor tip can be done without adverse effect, I have no idea as I have never tried it and have not known of anyone who has.

Michael

Arching Rotor / Distributor Cap

Reply #4 –
Thanks Michael:

Really appreciate the feedback from one who gone before me!

As you point out I am of the opinion the gap and proper venting is critical.  Whether caps (even though they have a vent) are really venting properly is an interesting question.

Not sure whether the multi-point rotor (just three stiff pieces of wire sticking out in place of the spade connector)  carried the spark from one wire to another or dropped the spark between each wire.  My guess is it dropped the spark and caused three rapid fires, in an attempt to get a complete burn.  I still recall I would get some oxidation on the wire tips, but very minimal and an easy clean.

Will check into the MSD Ford HEI Cap.

Not to beat the Aluminum / Brass issue to death but -- like yourself I always was of opinion aluminum was not as good as copper.  From a different perspective I recently replaced my house A/C condensing fan motor.  In  researching (believe AO Smith website) found an article indicating a number of electric motor manufacturers use aluminum in lieu of copper.  Again based on their research its not the material per se, but how that material is connected.  An improper connection (whether house electrical, or electric motor) the problem is oxidation at the connection point.  If properly connected, no problems.  For the normal person (non-manufacturing or special tools availability) I'm with you.

Re out gassing.  FWIW - Thinking back 24 years when I bought the car, I don't recall every having this problem.  I know for sure that Ford used the multi-point rotor.  I also believe (but not sure) that they used an un-vented cap.  Whether the multi-point is the key or a tigher gap was achieved using the wires is again unknown.

One last thought is whether polishing the rotor and terminal will help.  How you get into the distributor cap to polish the terminal is another issue!

Arching Rotor / Distributor Cap

Reply #5 –
Aluminum contacts in the dist cap have been corroding since the first one was installed... It's a fact of life... Does it really make a difference on performance??? Not that I've seen on a stock engine, and I seen some that looked like peeling tree bark...

What can you do to minimize it??? Use a brass contact cap, good spark plug wires and a plug gap of .045 or less...

BTW... AFIK you should never put dielectric grease on a rotor or dist cap contacts, the arc(not arch) will just burn it up, increasing your problem(At least you'll never catch me doing it)... It's main purpose is to enhance heat conductivity(TFI module mounting) or prevent spark plug boots from sticking...

Arching Rotor / Distributor Cap

Reply #6 –
I'll take a look at some Motorcraft info that I have. Maybe I can find something useful there (besides, it is good practice anyway). I do recall the multi-point rotors. Have you tried not using dielectric grease with the brass terminal caps?

The Aluminum vs. Brass issue is a good topic, seeing as those materials are used in nearly all caps and rotors. The ironic thing is that while Brass is used in many electrical parts as a conductor, it is also used as a dielectric, a "break" if you will, in plumbing and many automotive sensors and other parts that come into contact with coolant, aluminum, steel and galvanized/black cast iron pipe along with other parts. Plumbing codes require brass unions whenever joining piped of two different metals. The reason is that when water flows through pipes, a very small electrical current is generated in the metal piping. The brass union acts as a resistor that the low current cannot normally pass through. If the current is allowed to flow it will accelerate corrosion of pipes, especially at joints. As for Aluminum, you are absolutely correct. Also, when running Aluminum wiring, it has to be of larger gauge then copper for the same current capacity.

(the above was written but not posted this morning before TC50 replied)

TC50: It is kind of a catch 22 on the dielectric use. Some instructions say to use it, some don't. Experience seems to be the best way to make the call depending on the situation. As for using it on the TFI Module, I stopped using the nearly liquid  that comes with a new module several years ago. Using that stuff, or even the stuff in the tube, is not much better than spitting on the module before installing. It just does not hold up over time (meaning several months to a year or so); it does not take long before it starts to break down and vanish. I have been using Artic Silver 5 with great results on TFI Modules. It is thick, sticky, easy to apply to the correct thickness and does not breakdown too easily at temperatures experienced under the hood. Seeing as it is a compound for assisting heat transfer from Computer CPUs and GPUs I would expect it to perform quite well in a TFI application.

Arching Rotor / Distributor Cap

Reply #7 –
BUT if you check, I'm 99% sure brass is a better electrical conductor than aluminum(off to do that now)... As far as conducting electricity, when you're talking 20-30Kv, just about any metal is fine... Problem is, how does the metal hold up applying a almost continuous arc???

For heat sink compound, I use some from GC electronics that is designed to conduct heat away from power transistors and ICs in TV and other electronic equipment... Only problem is it's like a white putty and can be messy(don't use it on spark plug boots LOL)

[COLOR="Red"]Edit[/COLOR]... Nope brass is somewhat more resistive than... Didn't believe what I saw on the the net, so I looked it up in one of my old radio manuals... As I stated prior, 20Kv doesn't care squat about the additional resistance, the spark is traveling through resistance plug wires that have probably 100,000 times more resistance than that little piece of brass...

Arching Rotor / Distributor Cap

Reply #8 –
Contacted a Tech at Niehoff.  Interestingly his signature block was from Quality Assurance, Standard Motor Products

Here's his feedback:

1)  Multi-Point Rotor
These designs were all instituted to reduce RFI - radio frequency
interference - with other computerized components and sensors in the vehicle.  They were not actually designed to reduce arcing or terminal corrosion. We still use these designs along with the latest ceramic coated tip rotors to reduce RFI.

2) Arcing and corrosion are actually caused by the nitrogen oxide gas created from ionization. All distributors use some type of venting to remove these acidic gases - some are better at
it than others. Too much venting allows moisture to enter the
distributor - too little will cause acidic gases to build up.

3)  We do not recommend using any type of grease on the rotor tips or the cap terminals. The spark that jumps across the terminals will easily burn this grease off and create carbon particles that conduct
electricity - that will make the cap arc worse.

4) We also do not recommend polishing the terminals as we find this does not have any positive effect.

Recommendation
The best advice is:

1) Make sure your distributor is well vented and that the vents are clear.
2) Make sure the distributor shaft seal is tight and does not leak gases or condensation from the crankcase.
    (My Note: How do you determine whether gas is leaking?)
3) Make sure your PCV valve is working and pulling
moisture and gases from your crankcase.

4) Make sure there are no leaks in the distributor area. Especially check for AC lines or heater hoses that are dripping moisture or intake coolant leaks that could cause steam to enter the distributor vents.

Arching Rotor / Distributor Cap

Reply #9 –
MY note...

It's ARCING not arching...

Arching Rotor / Distributor Cap

Reply #10 –
TurboCoupe.  For some reason forum won't allow you to change Subject text even if you're the original poster.  Caught error just after started thread but couldn't change.

Arching Rotor / Distributor Cap

Reply #11 –
Quote from: dw85745;222511
TurboCoupe.  For some reason forum won't allow you to change Subject text even if you're the original poster.  Caught error just after started thread but couldn't change.

Yeah I see you corrected the arching error in yesterdays post(6-6) but you missed the one in the original post...

Quote from: dw85745;222053
1)  Will grinding an indentation in the rotor spad stop the arching
    and replicate the multi-point rotor?
2)  Will a new coil help (1984 original)?
3)  Any substitute (rotor or distributor) or solution that works?


Arching Rotor / Distributor Cap

Reply #12 –
Quote from: TurboCoupe50;222289
... Only problem is it's like a white putty and can be messy(don't use it on spark plug boots LOL) 


That would be a mess too... Probably would bake the wire boots to the plug :D

Quote from: TurboCoupe50;222289
... [COLOR="Red"]Edit[/COLOR]... Nope brass is somewhat more resistive than... Didn't believe what I saw on the the net, so I looked it up in one of my old radio manuals...


Sounds right... Probably the brass formulations (amount of impurities and "locked up" gases in the brass used) will have an effect of some sort though. I still feel the air gap is a big part of the issue as the larger the gap, the higher to voltage needed to "jump" the gap. I would think that factor would have a direct impact on corrosive gases caused by ionization and would make venting very important. However, I am not a materials engineer, chemist, metallurgist, physicist, or the like; I can only go off what I had learned as a mechanic and what experience and research has taught me since.

Quote from: dw85745;222397
Contacted a Tech at Niehoff.  Interestingly his signature block was from Quality Assurance, Standard Motor Products


Standard Motor Products owns several parts brands, including Niehoff. The tech's explanations seem sound as are his tips. Checking the PCV valve is an interesting one to put into the tips given, but valid. However, if you have a very high mileage engine with a fair amount of blowby, the PCV valve will have a diminished effect overall. That is not to say to ignore the PCV valve, it is just to point out that other issues could be causing some trouble also (like crank case gases getting into the distributer). Cleaning up the gray junk is a good thing to do and probably does help some (less arcing points). Polishing things, well, not sure where he got that from. I only use the emery cloth as part of a light cleanup of unwanted arcing points and it will not take off much of the harder material thus less opening of the air gap. I would still recommend finding the smallest that you can (if possible to do so). It certainly wouldn't hurt any thing. Where air gap info does not exist, try to use the recommend cap & rotor combination as set by the parts manufacturer until you find one that works (and make sure it is vented!).

 Oh, on the air gap, a worn distributer bushing could cause changes in air gap.

Arching Rotor / Distributor Cap

Reply #13 –
Quote from: GreyWolf30;222670
I still feel the air gap is a big part of the issue as the larger the gap, the higher to voltage needed to "jump" the gap.

I agree and is the reason I mentioned keeping plug gap at .045 or less... The spark not only has to jump from the rotor to cap, it has to jump the plug gap which is under compression... Since the air gaps are in series, the spark won't jump from the rotor to the cap until there is sufficient voltage to jump the plug gap as well... On a non boosted we're talking some where in the neighbor hood of 5-7Kv... This voltage goes up as plug gap or compression increases... The air gap is several million times more resistive than the brass/alu dist terminal, it's probably the least troublesome portion of the system even if it has some corrosion...

FYI it takes more voltage to jump the same gap under pressure than in the open... With additional pressure(boost) the requirement is higher still and is why the Turbo Coupes run .032 gap... Also you'll hear the term on boosted engines "the spark was blown out" which is not really true... Just the ignition system isn' powerful enough to to produce the voltage necessary to jump the gap... Could also be be weak plug wires that won't transfer enough voltage(I'm assuming the plugs are good but can easily be the problem on boosted engines)...

Arching Rotor / Distributor Cap

Reply #14 –
Quote
Posted by GreyWolf30
Polishing things, well, not sure where he got that from.

That was one of the questions I posed -- if polishing the terminal would help.  Original thought was the smoother the terminal less change for arc to fragment and possible create extra gases.
Per his response, non-issue so ignore.

A lot of manufacturers "private brand" -- just didn't realize Niehoff was being manufactured by Standard.  For info only.

Quote
TurboCoupe50
I agree and is the reason I mentioned keeping plug gap at .045 or less... The spark not only has to jump from the rotor to cap, it has to jump the plug gap which is under compression...

Good point about both gaps.  Never thought of it this way.

========================

In my case I just had my engine rebuilt, along with new plug wires, plugs, cap and rotor, etc. about 1000 miles ago.  That why of special interest.    As previously stated, buildup has been a problem for 10-15 years so rebuild obviously didn't help re-solve this particular issue.  Years ago used to run Motorcraft plugs and then switched to Bosch platinum but don't readily recall if plugs require a gap difference. 

David