My distributor cap exploded!!!

[K. Roman]

So,
I have a 1980 911SC 3.0 nothing fancy, basic infatuation etc. etc.

I drove it down to LA from SF on Wednesday, things seemed OK but I did feel that it felt a little overworked, but it made it.

On the trip back, about 80 miles north of LA, at the base of the Grapevine, I hear an explosion from the engine compartment. I pulled off of the road fearing that I'd eventually be run over by an out of control diesel truck and gave a look into the engine. I notice the orange distributor cap disinegrated in the explosion. What happened?
I called a towing company and fortunately had a shop. They replaced the cap and sent me on my way.

What I did notice was that the distributor had about six or eight little pins/hooks under the cap. the pins were bent up from the explosion.
I drove it another hundred miles and the cap exploded again!!

This time I was fortunate enough to be picked up by a guy who happened to be at the repair shop whose car was also undergoing some emergency work.
He passed by me and stopped when he recognized the car, picked me up and gave me a ride back to SF.

I have a brother in law who owns a towing company and luck for me he offered to pick the car up and have it towed to San Jose. He also owns an '83 930 and said he knows a wrench who would help and give me a "friend" rate.

Good news/Bad news.

Does anyone know what may have happened???

I read the Pelican board religiously but am just a lowly amatuer. If you can give me any advice, or understand the problem please feel free to respond.

Thanks for listening.

[sammyg2]

I've never heard of anything like that. For an explosion to happen you would have to have an ignition source (duh, we got that) and some sort of flammable vapor or gas inside the cap.
I suppose you could get some oil fumes from the crankcase up into the distributor, it aint suppose to happen but it is possible, then they could ignite. Maybe you have some fuel in your oil and that helped the ignition point a little.
Am I babbling? of course. It's 3:34 AM. It's a long shot but it's the only idea I have right now.
Did you see any evidence if oil in the distributor? Does you oil smell like gas at all?

[K. Roman]

No oil, but it did smell sort of sweet.
Sweet?

yeah, like burnt maple syrup.

[RoninLB]

only a guess that it was dizzy shaft play

[Wayne 962]

Picture of this phenomenon please!

-Wayne

[sammyg2]

Ya, what Ronin said, that rings a bell. If the dizzy shaft has enough play in it the rotor could hit the electrodes in the cap and shatter them,
I was going to say that but I hadn't thought if it yet

[69911e]

Make sure your rotor is an original Bosch, the spring clip in the rotor is intact and strong enough, and the rotor is fully seated on the shaft.

[yelcab1]

Can't be an explosion. Probably the dizzy shaft is a bit loose and spins out of concentric, shattering the cap in the process. Why don't you pull the shaft and inspect it.

[rs911t]

I had a rotor break and destroy the cap. Maybe shaft play or a loose/cracked rotor?

[Early_S_Man]

Turn your engine to TDC on cylinder #1 and pull out the distributor. You will probably find that the fiber washer on the drive shaft between the body and drive gear has disintegrated and is gone ... with a current end play exceeding 0.125" ... where it is supposed to be 0.005" or less!

[OSC911]

Just a thought but a few years ago when I was still a motor mechanic I had a similal problem whith and English car although I can't remember what. The cap exploded with no aparent reason. two caps later we decided to drill 4 holes into the cap so we could look and see what was going on. After a few minutes there was a blue flash which was not enough the explode the cap but it did explode on the test run - higher RPM and loan. To cut a long story short the engine had excessive fumes travelling up a worn distributor shaft bush causing an explosion ignighted by the secondary voltage of the coil.
Just a thought.

Todd
911SC

[Jgordon]

So the plan on the exploding distributor cap was to drill little holes and peer into it, on the expectation that you would see the cause of the explosion up close? That's ballsy.

[john walker's workshop]

i seriously doubt there was an actual explosion. most likely a byproduct of a wobbly shaft. grab the rotor and move it around sideways.

[twin plugged targa]

My vote is for endplay on the distributer shaft!.
My old 3.2 had this problem, the dreaded 86ragtop!!!!!!
As others mentioned remove the distributor and inspect the bottom of the shaft, others may be able to post pics of how it should look, sorry I have already erased the pold pics of how it should Not look!.
This destroyed rotors for me!.
Hope this helps
Ben