2 types of distributor caps ???

[puddin]

just wondering if their is any difference in the two types of distributor caps.. i'm on my second dizzy cap and seem to have a mis-fire to #1 plug-- using a timming light i noticed the spark skips out going to #1 every so often.. doesn't do it on any other cyl. and the coil wire flashes consistent... i worked it down to the cap or rotor-- i saved my old dizzy cap and rotor and put the old rotor with the new cap and runs good until 3000rpm then misses-- old cap and old rotor wouldn't run past 1500rpm. could it be runout on the dizzy shaft at higher rpm missing the #1 dizzy connector??? or rotor wear? i have been using the 5 accross dizzy cap - would the 3 on top and two below help or even make a difference?? i have a new coil with a crane cams xr700 iggy module - new wires and plugs. any ideas?????

**the reason i put a new dizzy cap on was that the brown is ugly so i painted it red -- looked good but the spray paint contains metal and shorts the spark out in the cap ....good light show

[ventura ace]

Check inside the cap for the depth to the outer contacts and to the center contact. There are different types of caps for the different distributors and rotor designs, and they all look identical on the outside, but are quite different on the inside. I ran several hundred miles on an engine that had the wrong cap, that was arcing about 1/2" accross all the contacts inside the cap until it finally carboned up and wouldn't run any more. I probably should have guessed something was screwy because every time I tried to adjust timing, I'd get shocked because it was easier for the electricity to jump through me than to jump accross the gaps. Also, it was firing all 4 plugs at the same time (a stronger spark on the closest contact and a weaker spark for the other 3 plugs).

Alvon

[puddin]

i guess i go back to the stock cap and rotor but not paint it--still pretty strange it only happens on #1 cyl...

while iam at it would adding vaccum advance help any ????

[azruss]

Never heard of different caps, Ace. Doesnt make sense to have the inside contact be ok and the outsides be out too far. The only thing that would make sense is a rotor that travels and elliptical path, and that i've never seen. Perhaps you mean that the caps have a different I.D. thus requiring a different rotor.

[So Cal Mark]

thinking that the rotor is spinning in an eliptical circle and missing #1 doesn't make sense. The contacts shouldn't touch anyway, and if the rotor was so far from 1 that the spark couldn't jump the gap would make the rotor contact the cap on the opposite side. Contact will break the rotor immediately. If the shaft had that much play in it, it should be readily apparent

[ventura ace]

Sorry, I didn't make myself clear. I'm not talking about the spark plug wire connections on the outside of the cap. These wire connections on the outside of caps look identical from cap to cap, though the inner design of the caps can be very, very different to accomodate different rotor designs for different distributors. If you measure the depth to the inside contacts of cap A, as compared to the depth to the inside contacts of cap B of the different design, there can be about 1/2" difference. That goes for the center contact, and also for the 4 contacts on the inner diameter. In my earlier post, I referred to the 4 contact on the inner diameter as the 'outer contacts', which I admit is confusing. Sorry for the wrong choice of words.

Hey, this may not be the problem with his engine, but then again, it could be. I can't explain why only #1 would be a problem, unless it is the first contact to get all carboned up from all the arcing. I'm just suggesting that is worthwhile to check the depth to the contacts on these caps. It was absolutely the problem with my engine.

Alvon

[manoa matt]

It depends on the distributor you are working on.

For the exhaust cam mounted double points models the caps are pretty much all the same, but there are several different rotor designs that work. The caps are bakelite with brass contacts while the rotors are usually a white nylon or black plastic.

For the electronic versions on 79-85 there are two types of caps. The original caps made from bakelite with brass contacts inside the cap. There are also caps made from plastic with aluminum contacts inside the cap. They look very similar, but the bakelite caps with brass contacts seam to work better. The aluminum contacts seam to erode quicker from the arching.

For the electronic distributors there are two rotors that will fit. The rotor designed for the electronic distributors has a resistor cast into the cap between the carbon button contact and the tip. The rotors designed for the single point block mounted distributors will also fit, but they do not have a resistor in the rotor, its a solid piece of brass.

If you have the stock electronic version and you are having misfiring above/around 3000 rpms check the control module behind the coil, also check the pickup wires for abrasion inside the cap.

As a general rule of thumb, you want to have a rotor and cap made with the same metals. Brass rotor contacts and brass cap contacts work well together and wear slowly. A brass or steel rotor with aluminum cap contacts will make the cap contacts wear away in a shorter time and increase the gap distance causing poor performance.

[So Cal Mark]

aluminum contacts would indicate a really cheap part, I'd avoid using any ignition parts with aluminum except in an emergency

[puddin]

i checked out (ohm with multimetere) the cap and rotor -- checked good

i checked the centifigal (sp) weights and springs -- looked good

by using the timing light i found that at above 3000 rpm the #1 and #3 cyl had a miss (no spark ) random frequency

i found that the center (carbon) post which is spring loaded was running and elepecical (sp) path on the rotor so i emery clothed the rotor contacts and replaced the carbon post and spring .. it runs fine now also cleaned the 4 cyl brass contacts in the dizzy cap and they have wear spots center of the contact area so the rotor and cap are correct parts

i suppose at higher rpm the carbon spring loaded contact would fload up or not make good contact -- so far she runs good again just too damn cold to drive around

thanks guys
mark

[puddin]

messed around with the dizzy again here's what i learned

there is a approx 2mm gap between the rotor and dizzy contact-- i know it shouldn't touch but that's a large gap for now reason it seems to me that the rotor contact is circular and would allow it to graze the contact????

rotor seems to be fully pushed up into dizzy when mounted-- after cleaning the dizzy contacts with emery cloth i remounted everything and seen the wear marks == is it neccessary to have the rotor pushing that hard on the spring loaded carbon contact ???

carbon tip (center contact on dizzy) seems to be moving in ellipicatal (sp) path
making carbon dust around inside of dizzy not due to rotor wobble but the play between carbon contact and it's brass sleeve

rotor seems to be able to move 2-3 mm on shaft even when the metal fastening tab
is really tight -- wouldn't this alter timming ??? i used some crazy glue to secure it tight and it runs really well now

[TulsaSpider]

Perhaps you are missing the thin strip of metal that is supposed to keep it in place? It fits between the shaft and the rotor