Distributor cap question

[Linda]

I was checking the distributor cap and rotor and both had some black carbon-like deposits. Problem is that as soon as it gets cleaned off it soon reappears. Is this normal? A clean cap and rotor help the car run smoother so I wonder if there is anything that can maintain that.

Linda

[K1200 GT]

The carbon shouldnt have that much effect. Unless there is a crack in the cap you cant see. The little black button in the cap is made of carbon if im not mistaken. The pits in the terminals and rotor have a big effect cause they get further from each other as they wear. Replace the cap and see if that helps. Use an eraser to remove carbon where you can.

Rich

[spl310]

Carbon tracking CAN cause big problems if they complete a circuit from one contact to another.

[notoptoy]

I always use a little bit (THIN smear) of dielectric grease on all the contacts and the button, both inside the cap, on the rotor and in external cap contacts. All my EI dizzies get sent out pre-greased this way. Also look for good quality caps - brass contacts with a brass rotor as well. The aluminum stuff is junk and wears out much more quickly.

[K1200 GT]

Yabut have you ever seen a cap that bad unless it had 30-40000 miles on it. And its time to replace it any way.

Rich

[Linda]

I'm getting an Echlin brand cap and rotor with the brass contacts. There was a little pitting on the old Echlin cap so I am replacing even though it doesn't have a lot of mileage.
Thanks for info

Linda

[dbrick]

I'm getting an Echlin brand cap and rotor with the brass contacts. There was a little pitting on the old Echlin cap so I am replacing even though it doesn't have a lot of mileage.
Thanks for info

Linda

Echlin's is one of the best, should easily last 25K miles. If there were carbon tracks, they look like thin squiggly pencil lines usually from terminal to terminal. It's funny, couldn't find a decent photo of carbon tracking....Alvin??? Keep your old caps as a spare, you'll probably never need it, but someone else on the road might. Caps with a smooth interior are more prone to this, high humidity helps too. That's the reason caps have all those concentric ridges and little dividers on the inside, to effectivly lengthen the distance. Larger diameter caps are better, more spacing, but a small 4 cyl has as much space as a big 8 cyl, so not a big problem even for the stock cap.

[Lee2000]

Make sure any cap you put on there has a vent hole to get rid of ozone...drill through the cap to create a vent if you have to.

[dbrick]

Make sure any cap you put on there has a vent hole to get rid of ozone...drill through the cap to create a vent if you have to.

The distributors are vented on the bottom of the casting, think that would be enough?

[fossil]

The materials for distributor caps have a significant effect on their performance and durability. The plastic material on the cap is the most important consideration because it is where tracking and carbon arcs go. There are compression molded thermoset ones that are most resistant to tracking. There are cheap injection molded thermoplastic ones that do not offer as much resistance to tracking. Actual material selection is critical to good performance. Surface finish of the inside of the cap also has an effect on tracking.

Aluminum contact terminals are not junk. Nissan caps in almost all instances have aluminum contact terminals. I have used Nissan distributor caps with aluminum terminals for many years and they have provided good service. I use them on an old Nissan pickup that has 8 sparkplugs and they last 70K to 80K miles without terminal failure or carbon tracking. The last roadster distributors that came from Nissan had aluminum contact terminals as they had for years.

I have built a number of EI distributors for roadsters over more than 10 years and have not heard of any failures of the aluminum contact terminals.

Stan

[Linda]

Good to know but if given a choice I think I would still prefer brass, i notice alot of hi end caps use brass. Interesting about the importance of the plastic material

Linda

[notoptoy]

Fair enough point Stan, I will clarify my comment in that the typical, cheap, off the shelf aluminum contacts are rarely of high quality. My experiences outside of Roadsters (mostly american V8's) have never been good with Aluminum contacts. So not to short the whole group, I am sure that there are high quality aluminum contact caps, including Nissan. I just find it easier for me, and that it adds to my piece of mind, to spend a little more to go brass.
Plus they look better too

[Lee2000]

Make sure any cap you put on there has a vent hole to get rid of ozone...drill through the cap to create a vent if you have to.

The distributors are vented on the bottom of the casting, think that would be enough?

I'm sure the cap makers considered the venting requirement in their design work...it's just that all the dizzy caps I've owned were vented(with intregal water/dust shields) right up near the contacts.

[dbrick]

Whether from design or marketing, I found most of the top end aftermarket caps come with brass terminals. Maybe it's a buzzword that helps sales because brass is percieved as better by the public or it works better with brass plug wire terminals? For carbon though, I would have to agree that the material of the cap, along with design is important. I think the Accel caps I had a few years ago were Alkylid, very dense, Mallory uses the same, as does Napa/Echlin in their top line caps. More like a Bakelite than a plastic.
Only thing I could say is if they bother to use brass terminals, the rest of the cap is probably of a higher quality than average aftermarket, and as Stan said, brass or not, the Nissans have apparently proven themselves.

Material of the rotor and the length of the blade is a factor on the EI units, length can vary and adds alot of extra arcing from the larger gap to the cap terminals from a smaller effective diameter. More arc, more carbon, more ozone.

[spl310]

As I recall, a lot of OEM American distributor caps with electronic ignition are aluminum contact units.