As TopHatChef has experienced:
https://www.jaguarforums.com/forum/x...g-wells-90790/

... it appears the Spark Plug Boss Seals (SPBS) on my XJ6 have **prematurely** worn.

On 07.13.2012 (10k-15k miles ago?), I replaced all six SPBS's, along with the valve-cover gasket. On the way home from the office yesterday, I felt that "as if running on 1/2 the cylinders" engine shuddering.

I pulled each of the 6 coils, and sure enough, the bores were filled with oil. The forward two bores were the worse, oil filled 1/2 way up the plugs, the 4 aft bores had about a teaspoon+ of oil (the aft-2 cylinders had the least oil). As suggested by Grant, I used a light coat of RTV on the seals prior to installing the valve cover.

Should i expect to perform this seal-swap on an annual basis?

 

You'll probably know more when you have it apart (again) and can examine the seals, as the nature of the problem might become apparent on examination.

But, no, annual replacement isn't to be expected. I replaced mine 60k miles ago (3 years ago) and all's well.

Cheers
DD

 

The problems I have read about and found about thi issue are as follows.

Porosity of the cam cover in the area of the spark plug tubes, and oil seeps thru the mag/alloy and fills the tubes. This I have never seen, only read about. BMW have this issue also with some of their V8's.

The "crush" of the cover, via the bolts and the seals around the edge of the cover that control this "crush". My meaning is that with the bolts installed and nipped up (they are shanked, so no matter how much you tighten them, they wont get any shorter) the length from the underside of the top washer TO the face of the cylinder head is a FIXED distance. The cam cover/gasket/SPBS/bolt seals, all equate to this FIXED length "plus some magical amount" to apply the "crush" to make the seals actually work.

Those bolts seals compress over time, and are rarely replaced. This effectively reduces the "crush" and oil finds it way into unwanted places.

I apply Hi-Temp RTV to both sides of those tube seals, ensure both metal faces are CLEAN.

No leaks.

 

Thanks for the detailed response, Grant.

Well, here's why Cyl 1 is leaking (webpage with 6 photos):

XJ6 Spark Plug Boss Seal

For whatever reason, Cyl 1's boss seal got squashed on one "end" (photo 2 shows Cyl 1 and 2) ...

Something odd I didn't notice the last time I had the cam-cover off ... what the heck has happened to Cyl 1 bore wall's inner surface? (close-ups in photo 3 and 4). Looks like it's been sheared away ?!?!? In photo 2, we can compare Cyl 1 to Cyl 2's wall's inner surface.

So I've added a new photo (#5) since i originally posted this reply ... I've laid a straight-edge across the top of all the spark plug bores ... notice Cyl 1 inside "ring" is pushed up.

I suspect this means I need to hunt for a valve cover ... I see an internal stamping of "NBC 2553 CB/C" ... but quick research reveals Part #s NBC2564CA and NBC2564CB

 

BUGGA.

Never seen that before.

The bore oddity looks like arcing blasting (if that makes sense), from the oil covering teh plugs/coils.

The height variances is a weird one indeed.

A replacement cover is the best option I have at the moment.

I know you are in the USA, and never got the 3.2ltr engine, but the covers are the same, which might assist you a tad when looking, as most of the world other markets got the mighty 3.2 engine.

I've added some more JD to my morning coffee as a sympathy gesture.

 

How thoughtful! That's one of the reasons we love you so much, Grant. You always put everyone else's feelings first


Cheers
DD

 

Maaaaaate.

I am trying HAHAHA, to find an intermittent misfire in one of the S Type.

FAIR DINKUM, I would rather have a 30 years sadly neglected V12 to sort, sooooooo much easier to understand.

I will get there one day.

MORE

 

Well, for my AJ16, I tracked down a guy in England who was selling new old stocked, jaguar boxed, never opened cam covers that came with brand new bolts and gaskets.I bought two for good measure. Had one installed according to Jaguar bolt pattern specifications.

Today I popped the bonnet for unrelated maintenance, and what do I find??!
-----cam cover oil weeps.

Not very happy. I am hoping that the bolts just need to be retightened. If not, I am giving up on having a leak free cam cover. Nothing else I could humanly do.

 

That was my thought too. I've examined the coil for Cyl #1 (which I dated 08/2012), so I replaced it about 16 months ago ... there are no cracks in the coil's housing and the rubber boot to the spark plug is like-new.

Still, the metal appears to have been 'eaten away' with a combination of super-heat and some arcing. I can't explain it.

 

I read somehwere, and I truly forget where, which is a tad concerning.

The cover is "Magnesium Alloy", as are many cars, BMW, Chev, Jag, etc, and electrolysis is the culprit here.

Most I read were attempting to "repaint" their covers, and some just crumbled as preperation was being undertaken.

A poor mix of the alloys at production also got a mention.

One that got my attention was the BMW V8 guy that believed it was due to bad earths on his engine. Based the fact his earth strap was damaged to the point of only making a few strands contact. A tad far fetched I thought, BUT, earth strap issues are common on Jags mainly the V12 cars, but maybe he has a point. I added an extra earth cable to my 3.2 waaaaaay back, and have thought nothing more of it.

Anyway, none of this sorts your car, you need another camcover. I dont have one. I got a crankshaft, conrods/pistons, and odds and ends for an AJ6 engine, but no camcover.

I still reckon the UK will be your best place, even with shipping.

 

I'll be sure to check the grounds while i wait for a cam cover. I really would like to know what happened to Cyl #1 spark plug bore ... if the underlying cause still exists, another cover will simply fail the same way over time.

I found two on eBay in the US ... ordered one for $59 USD (free shipping) - hopefully will be here by the weekend. I also found one at a local Jag repair shop, but they want $300 USD.