What the heck happened to my Rotor and Cap?!?

bit · bit's Garage

Hi Guys,

So I put about 20k kms on my car this past summer. I changed my rotor and cap at the end of the previous summer, so I figure there is is about 23k on these two items.

The last time I bothered to check my rotor, was just after I had my distributor recurved a couple of months ago (about 10k ago) and everything looked just fine, and the car ran great (read my post on it at 1980 911SC Distributor Recurve Results .

About three weeks ago, I noticed my car hestitate a bit when it was cold in the mornings. I wasn't very bad or noticble, but I knew it was there. I did take my car out during a couple of major downpours here in Vancouver, and figured it was just a bit of moisture in the cap since it would clear up one it warmed up.

About a week ago after being out in the rain during a downpur again (ah Vancouver weather), it was sputtering a little bit as usual when cold, but it also started hestitating ever so slighly once warm too.

So I looked under the cap to see what's up, and yes there was a bit of condensation on the roof. BUT the center conductor was all bubbly,brittle and appeared to be burnt! The top of the rotor was black and charred! I just touched the center conductor with my finger ever so lightly, and the plastic and the center thing disintergrated into dust!! WOW, I don't even know whow it ran like this. I had a spare an swapped both items, but what gives? I've been checking the new cap/rotor since I swapped them in and drove about 2k on them now and see nothing that would lead to this. Plus I have been driving the car pretty hard recently since it is soon to go into hibernation (like tomorrow).

It seems that the center was just running too hot! I do have an MSD 6AL and MSD Blaster Coil, could these be factors? 23k on a cap and rotor is a bit much, but when I looked about two months ago, they still seemed just fine.

Any comments would be appreciated.

Thanks.

.Steven
1980 911SC

RoninLB · 11-12-2004, 10:57 PM

Quote:

Originally posted by bit

Any comments would be appreciated.

only speculation.
I remember that a pelicanhead thought that an MSD contributed to a toasted rpm limit rotor.. that the graphite/whatever got beat up. So I'm interested in your situation.

so I can only guess that a slightly worn cap&rotor had enough load to provoke the MSD to zip to various parts of a wet/damp cap&rotor. I've seen alot of missfires from very damp internal caps in small boats, but nothing like yours.

Early_S_Man · 11-13-2004, 12:25 AM

Looks like a fairly normal situation for a system with MSD ... first the carbon 'button' contacting the rotor fried and fell out, and then the rotor itself was overstressed and burned out!

SpeedracerIndy · 11-13-2004, 03:41 AM

It could be worse, this is what I found once:

Joeaksa · 11-13-2004, 06:48 AM

While in there check the distributor and see how tight the bushings are.

JoeA

Lorenfb · 11-13-2004, 06:54 AM

Warren is right. That's the problem of using a CDI system with too much spark energy & voltage. Go back to the stock Bosch CDI.

john walker's workshop · 11-13-2004, 08:41 AM

that's a cheap aftermarket cap. ie: non-bosch, and the quality lacks. use the good stuff.

RoninLB · 11-13-2004, 10:56 AM

one real deal is brand new, one has maybe 20k mi. The worn center tit is another indication. The worn cap was not with a MSD... I only have 2k mi on my MSD.

john walker's workshop · 11:36 AM

the flat sides are still on the center carbon, so it can't be worn much. it looks like the rotor has been raising up and rubbing on the cap. the fibre thrust shims above the drive gear may be gone.

Randy Webb · 11-13-2004, 12:03 PM

Related question -- with a MSD, how often should you replace the caps & rotor? It's going thru a dual dist. (964) if that matters?

RoninLB · 11-13-2004, 03:55 PM

I finger nail picked some carbon off the outside around the tit. Dizzy linear play about .030 installed.

Randy... I flip the cap and rotor around valve adjustment, generally.

jenior · 11-14-2004, 04:29 PM

I think there are other issues with that cap rotor..I ran out and looked at my cap rotor and it looked still like new. I have about 20k on rebuilt..
I have the MSD 6A.......Jesse

john70t · 11-14-2004, 05:27 PM

One thing to make sure of is that the rotor is fully seated. I destroyed a set that way when the rotor worked it`s way upwards and started shaving itself on the sides.
That Niehoff may have also failed from heat stress/cheaply made. I`ve seen a Bosche that didn`t have continuity between the button and the tower(hmm), but with the rpm-limiting spring it`s still probably the best made brand for the application.

fred cook · fred cook's Garage

Don't listen to the "nay sayers" about the MSD ignition. I put an MSD 6A unit on my SC when the Bosch CDI failed and it has run perfectly ever since. As mentioned above, use the Bosch cap and rotor and make certain they are installed properly. I replace the cap and rotor once a year on my car (about 10-12,000 miles) and they are still in good useable condition at that mileage.

Good luck!

Fred Cook
'80 911SC coupe