Another Gnarly MSD Distributor Cap
 

When I was undergoing my carb woes, I replaced the cap & rotor. This cap was still functioning pretty well, but it's a bit worse for wear considering it only has less than 4,000 miles on it. The black stuff around the perimeter is from the little ball at the top of the cap that the rotor prong touches -- and the eight electrodes all look like they've been nibbled on.

http://www.clubcobra.com/photopost/data/500/cap001.jpg

While it looks kinda ugly I wouldn't think it would be a serious issue as far as miss firing goes?

I think it was actually working just fine... or fine enough, at least. But it was obviously past its prime.

Yeah, I hear that. I likely would have replaced it as well. Seems to me about 4 to 5,000 miles is all you get anyway before the dang center electrode breaks! :)

I continue to have this happen, and don't know why. The center ball disintegrated once, and since then I get what you have in the pic above along with some white hardened pieces on the tips of the pins.

same thing here only something seems to be missing in the middle **) :JEKYLHYDE

at the end of this season a duraspark will reside in my motor, msd can kiss it

Mine looks the same after a season of driving. So while stored for the winter I take a small round brass brush in my dremel tool & clean up the contacts & rotor tip nice & shiny clean. Then wash them out with brake cleaner & compressed air.
So far 20,000 + miles & working fine. The corrosion/eroding on the cap does not appear to get any worse from year to year, so far!

Maybe I'm just a cheapscape,:D:D but it's working for me.

Craig

+1

I have a duraspark. Not as sexy or colorful as an MSD. Works though.

I replaced the rotor and cap last year just for fun. Got it from the friendly NAPA man. I think it was same as a '91 Crown Vic. Reliable car.

Jack

when the electrodes get like this no amount of cleaning can put back the material that has been vaporized, it may look shiny, but your rotor contact is getting farther and farther away from the electrodes. now the brake clean on the plastic cap is a whole other story.......

Like I said---Works for me 20,000 mi + & counting, I also get 22mpg average & can accelerate quite nicely @ 1500 rpm in high gear with no missing & can hit the 6000 limiter in 1st. & 2nd (too chicken $hit for more) without skipping a beat.
Good enough for me.

Craig

Why these caps burn up
 

Purple Venom Here is the problem and their fix
Old caps had a spring and a steel/copper center post, with a normal coil up to about 40K volts, it had no problem You could get many years out of it.
The problem started with Accell super coils back in the 70's, MORE POWER. Basicly you are arch welding inside the cap
To slow down the burning of the rotor and cap post the extended the rotors air gap to kill some of the spark, this fixed the problem up to 60K volts.
Today 60-100K coils getting to be the norm or coil on plug setup. The centers are carbon, it's the only way to not melt the center contact. Too much heat and even the carbon is burnt out. Some of the guys are using one of the old GM caps from autozone or Pep boys. I don't have the cap or rotor numbers but say they are having good luck with them. I have seen one cap and rotor with a hole through the rotor spring end and the cap melted in the center area. The fix is to lower the coil output. The MSD still will give you about 20 degrees of spark to the plug. I have a friend running the Nology spark plug wires that have capacitors in each wire. They are not cheap and have to be grounded to the motor block and have a good ground also. This may be a way around the burnt cap and rotor problem.
Pat your cap looks pretty good for 4K miles on it. I'm on cap #3 and rotor #2 from racing with HVC MSD coil. Rick L.

Keep your plug gaps on the small side. Pull up on the rotor contact to ensure that it touches the center button. Drill an extra vent hole in the cap to release the ionized air.

MSDs are capacitive ignitions. They hit the primary side of the coil with hundreds of volts instead of the old 12ish. Capacitive ignitions make for short duration and high energy sparks. The short duration is why MSD requires multiple hits at low RPM. But you ignition is seeing more sparks per revolution that you would intuitively expect - hence the accelerated cap & rotor wear.

It does not really matter how much "potential" voltage a coil has, as long as it has enough. Electricity is lazy - if it takes 8,000 volts to jump the system gaps, 8,000 volts is all you get.

barry,

you mentioned running a tighter plug gap? tighter than .045? what gap would you run? msd pro billit, edel heads

i'm at the school of thought that i see no advantage to the msd dist. and 6AL box. other than a rev limiter. i'm leaning to duraspark dist, with a ford box.
if my valvetrain can live to 8000 rpm and my manifold is all in at 6500 then i think with a shift light i won't miss my shift by 1500 rpm.

One advantage is the multiple spark discharge that occurs in the lower rpm ranges. This keeps the plugs burning extra clean and assures a more complete combustion than a single spark system, like the dura spark. The downside of the extra clean plugs is it makes it all but impossible to "read" them, if you were so inclined to do so. Most folks either don't know how or don't bother.

Interesting what Barry said about plug gaps . I was talking to Rob Pond the other day and he said he preferred .035 gap and no larger than .040 ( for many reasons ) .... every engine builder has his preferences and valid reasons to back them up . Plugs were AR 3923 .
Ernie ... correct , the new MSD ignition systems make it more difficult to read a plug , but where you really must read a plug for WOT mixture is at the base of the insulator , and that is shielded so you can get a good reading of the fuel ring , which will be a ring about 1/16" wide and a light gray if WOT mixture is correct . It takes at least one 1/4 mile run at full throttle and a clean engine cut to be color the insulator .... and a GOOD plug reading light . You can be dead on for WOT and still have a white insulator . Mid range , as you said is more difficult .

I'm running a Standard Ignition "Blue Streak" cap 'n rotor on my Pro Billet and have had it on for 9,000 miles (3 years) and it still works fine. It's for a "points" SBC. Dump the MSD caps.

I carry an extra MSD cap and rotor in the trunk with my standard fare of tools and supplies when on the road just for these reasons.

Plugs and Gaps
 

My engine builder recommended a gap of .040 and the Champion RC9YC5 plugs, which is what I use with my full MSD setup and my Edelbrock heads. Edelbrock recommended one notch warmer, the RC12YC5 plugs in fact. MSD recommends that you go colder than what the head manufacturers recommend, so I guess they would want to see the RC9YC5 plugs. They also recommend a little bit wider gap than .040 with a 10.6 to 1 compression ratio, like I have. I've always had good luck with Champions, but WTF, there's no shortage of guys that say they're crap either.:p

yeah, i'm not a big fan of champion, i've been using the autolites 3924, gapped at .045,
in edel heads, i'm going to try the .040 gap as a see what happens. i have a new msd cap in stock to use but it will be the last one i will buy. i made note of the blue streak cap, any others out there that might be a contender? the msd woes with the cap i feel are a problem not with the type of ignition but the quality of the components. i have been using msd and mallory since the late 70's and never ever did i have this problem with caps. so onward and upward.......