[v12-engine] Second Post - The Amazing Exploding Distributor Cap

V12-Engine
1

This is my second or part II post.

About a week ago, as I was running tests on the engine to
determine the cause for the smoking issue, as I was starting
the engine I heard a pop and then the engine ran normally.

Yesterday, in anticipation of today’s disassembly, I started
the car, heard a thump and then the engine ran normally
again. Honest!!!

As you look at the pictures on my website:

http://members.shaw.ca/awparran/Jaguar/

You have got to ask yousrself, am I smoking a whacky weed or
what? I can assure you that I am not. After seeing the
damage, I too find it hard to believe the car was even running.

I have read about exploding distrubutor caps caused by a
buildup of oils in the vacuum line leading to the AAV tube.
I have inspected the line and it is clear.

Now for some head scratching.

As you can see, the ‘‘T’’ from the AAV is melted. Thus would
cause no vaccum to be extracted from the distrubutor cap.
Why did it melt? I dont’t remember it getting caught
anyplace hot.

This might cause other problems, but not an explosion.

Now for the kicker.

When I wrote my post last week, before I began my
investigation about the smoking issue, I noticed I had a
major fuel leak on the #2A injector. I guess the new hose
had not sealed properly, or maybe I had cut it too short.

Anyway, I had seen the leak before and it went away, but
this time it was a major problem. I cut a new hose about
1/8’’ longer and replaced the hose. The leak went went away
completely.

I started the car, heard a pop. Investigated, saw nothing,
and started the car again. The car ran smoothly after warm up.

So unless anyone says different, here is what I think happened.

The accumulated gas pooled around the distributor. The pop
I heard came from within the cap as the fumes ignited. I did
not see anything, but there might have been a fire inside
the cap, which went out after the fuel was consumed.

The distributor cap was destroyed, but I could not see it at
the time.

I believe the ‘‘T’’ fitting had nothing to do with the
destruction, and as stated I think I would have seen other
problems. I also think the ‘‘T’’ melted as the flames were
being sucked back into the engine.

Why the car even ran is beyond me. I guess the plug wires
were holding the cap remains just right.

Amazing!!

Tony–
TonyP '84 V12 Vanden Plas
Kamloops, British Columbia, Canada
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2

Tony,

I had a very similar experience. See the distributor cap photos
at my Web site.

My theory is similar to yours, but goes deeper. I’ve offered
it before and it has had dispersions cast upon it by some really
good people. I think leaky FI hoses etc. allow fuel to leak down
into the crank case around the valley cover. I’ll bet if you remove
your you will find the old, thin paper gasket virtually nonexistent.

From there, under influence of crankcase pressure due to blow-by
and marginal PVC operation, the vapor is pushed up through the
shaft seal and into the distributor. In my case there was evidence of
burning in the area around the distributor, probably set off by
the event in the distributor when it popped open.

In my case also the engine continued to function. Indeed, it ran
so well I discovered the damage some unknown time after the event.
Just happened to be looking around the engine and thought
“what’s that blue bit down there in the bottom of the vee?”

So, my advice is to replace the cover gasket, and change your oil.

As to the oil under the cam covers, it might also have to do with
crankcase pressure. I can’t say exactly how, Maybe the pressure from
the crankcase is simply too high to allow the oil to flow down?
I’m way out of my depth here, but it’s a theory. When a bunch
of things happen at the same time I’m inclined to think they’re
related. I would check the PVC system… the valve and the breather
elbow on the left head.

Ed Sowell
76 XJ-S
http://www.efsowell.us/ed/myJag.html

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3

In reply to a message from Ed Sowell sent Fri 5 Aug 2005:

Hi Ed:

Thanks. As stated in my SMOKE post, I had checked the PVC
valve and it was clean and free. Never knew about the paper
in the VEE. I will check it too.

The oil was replaced last month when I removed the oil and
transmission pans.

As for pressure in the crankcase, would it not allow the oil
to drain when the engine is stopped?

As you might have seen in the pictures, even before I
removed the cover, with the bolts loose, oil was just
flowing out of the back. I had to put thick wads of paper
towels between the engine block and frame to absord it all.
There must have been at least 1/4 of a quart dripping down.

I guess my next step is to take the cam out and see what is
or isn’t underneath, along with removing the crankcase cover.

Tony–
The original message included these comments:

So, my advice is to replace the cover gasket, and change your oil.
As to the oil under the cam covers, it might also have to do with
crankcase pressure. I can’t say exactly how, Maybe the pressure from

–
TonyP '84 V12 Vanden Plas
Kamloops, British Columbia, Canada
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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4

TonyP '84 V12 Vanden Plas wrote:

As you might have seen in the pictures, even before I
removed the cover, with the bolts loose, oil was just
flowing out of the back. I had to put thick wads of paper
towels between the engine block and frame to absord it all.
There must have been at least 1/4 of a quart dripping down.

Oh, yeah, that ain’t right. One way or another, I think you’re on
the right track. Have you tried just poking something down that slot
behind the last cam bearing cap?

– Kirbert

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5

TonyP '84 V12 Vanden Plas wrote:

Yesterday, in anticipation of today’s disassembly, I started
the car, heard a thump and then the engine ran normally
again. Honest!!!

Y’know, there are those who suggest that the distributor ventilation
scheme was intended to prevent this from happening. If that was
really the objective, clearly it ain’t working – your cap is vented.

– Kirbert

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6

In reply to a message from Kirbert sent Fri 5 Aug 2005:

These no doubt about it now. :slight_smile:

Tony–
The original message included these comments:

really the objective, clearly it ain’t working – your cap is vented.

–
TonyP '84 V12 Vanden Plas
Kamloops, British Columbia, Canada
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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7

In reply to a message from Kirbert sent Fri 5 Aug 2005:

There’s no doubt about it now. :slight_smile:

Tony–
The original message included these comments:

really the objective, clearly it ain’t working – your cap is vented.

–
TonyP '84 V12 Vanden Plas
Kamloops, British Columbia, Canada
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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8

In reply to a message from Kirbert sent Fri 5 Aug 2005:

I’m going to try that today.

Tony–
The original message included these comments:

Oh, yeah, that ain’t right. One way or another, I think you’re on
the right track. Have you tried just poking something down that slot

–
TonyP '84 V12 Vanden Plas
Kamloops, British Columbia, Canada
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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9

Hi Tony,

Hi Ed:

Thanks. As stated in my SMOKE post, I had checked the PVC
valve and it was clean and free. Never knew about the paper
in the VEE. I will check it too.

The oblong cover is over a gallery where you can see the shaft driving the
distributor. It drains down into the crankcase. Although the paper
gasket is still sold by some Jaguar parts suppliers I used one
of the newer ones.

The oil was replaced last month when I removed the oil and
transmission pans.

Before of after the fuel leak?

As for pressure in the crankcase, would it not allow the oil
to drain when the engine is stopped?

Yeah, it was a harebrained suggestion.

As you might have seen in the pictures, even before I
removed the cover, with the bolts loose, oil was just
flowing out of the back. I had to put thick wads of paper
towels between the engine block and frame to absord it all.
There must have been at least 1/4 of a quart dripping down.

With all the work you’ve done is it possible that a piece of debris
i.e., bits of old gasket, was left in in the patient, later to
be caught in some small drain hole?

I guess my next step is to take the cam out and see what is
or isn’t underneath, along with removing the crankcase cover.

This is a suspenseful story. Can’t wait till the end!

Good luck.

Ed Sowell
76 XJ-S
http://www.efsowell.us/ed/myJag.html

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