Just changed all 12. What do you think about the condition of the old plugs that I removed? All comments welcome 🤗

 

Here is a couple of things I notice: Had the engine been running before you removed the plugs in the picture? Had it been driven and thoroughly warmed up or was it just started for a few minutes to pull it into the garage, for instance. All of the plugs have a shiny appearance and the threads are wet. I don't know the firing order for a V12, so I'll say #1 and #6 on the left bank are using some oil and/or running rich. #7,8,9 and #12 on the right bank are doing the same. None of the electrodes have the dull, matte appearance of being hot recently and they are all perfectly squared off on the ends suggesting the plugs (in the picture) are fairly new. The oil on the threads would not be a normal condition to me and might indicate some oil getting past the piston rings.

Now, you tell us, how does/did the engine run? What caused you to change plugs?

Dave

 

Pretty mormal for a PreHE.

1973, would be Carbies, so rich running is normalish, and the fact, mentioned above, the engine has had way too many start/stop cycles without getting it to temp BEFORE shutdown.

The V12, of any vintage, should (must in my fleet) be run to temp once started before shutting it down, so some pre-planning is always needed.

The Infected PrehE with teh D Jetronic system will flood in a heartbeat if treated this way too long.

Mine are sooty, usually coz we have this STUPID 50KPH speed limits, so getting is revving long enough to clean it out is hard.

My1976 XJ12 lays a decent smoke screen (brown shitty colour) whenever I get the chance to squirt it to Redline, and then its sweet as it should be till the next time.

Then the owners that are afraid to "drive it as designed" for fear of breaking something, its a V12, and a Jag,
"kiss the redline as often as you can" is a very common suggestion on here, and its what they need.

The oil, oh well, camcover gaskets do leak on these, and are a Mongrel to change. At least the plugs wont seize in the threads.

 

Does this apply to the 4.2L 6 cyl. also? the most I've pushed mine to is perhaps 4,000 RPM.

(Then the owners that are afraid to "drive it as designed" for fear of breaking something, its a V12, and a Jag,
"kiss the redline as often as you can" is a very common suggestion on here, and its what they need.)

 

🤞 because I do it often.

 

YES.

Daughter actually "moved" the Redline on her S2 4.2, claiming she got 500 more RPM out of it. She was 18, and even put a dent in the floor, thinking the Go Faster Pedal would move further, she had a lot to learn, but at least she was "thinking", unlike many today.

That was 18+ years ago, its still as sweet as. She built that engine at 18yo, and still has it. She be 36 now.

The V12 is just mush better.

 

The engine needs to be well-warmed, then run at highway speed for some distance, shut down as quickly as possible then a "plug chop" is done to enable one to see what's actually happening in there.

A well-lit peek of the insulators is also necessary to see how things are doing re. mixture, timing.

Plugs tell a surprisingly detailed and accurate story of what's actually going on inside an engine.

 

Norfolk Enchants,
What say you?

Dave

 

Thank-you for all the great advice and learned comments, much appreciated.

It is indeed the carb variant. Some further comments and answers to your questions:

I let the car sit for about a month with the plugs soaked in penetrating fluid before I removed them. I think this is the dark glossy look on the threads that can be seen.

Your short-journey and start up is correct. I have been struggling with a transmission issue that limits the driving time (starts slipping after after driving about 0.5 miles), so it has been difficult to fully warm her up. Spot on guys!

I was super interested how some of the plugs looked sooted up, and others looked like the were running clean. Notwithstanding potentially burning oil on those cylinders as Dave mentions, I wasn't sure if some sort of mixture richness imbalance across those plugs is “normal” for the carb versions?

 

The plot thickens.

That would be a BW12 transmission, and Parts are hard to find these days, NOT impossible just harder than normal. Then finding someone that can rebuild the thing..
One of mine lost forward about 5 years ago, still went backwards, but thats annoying.

Low fluid is a killer on them., and I run them about 1ltr over the full when HOT.

Looked at swapping for the TH400, nope, different crankshaft used, bugga.

I seriously doubt there are many, if any, multi carby cars that have a good consistent burn to the plugs. Carbies were a good compromise and did an awesome job, but emission nonsense deemed them obsolete.

Setting up those 4 Stromberg CD carbs is an art, and it took me many months to get mine spot on, lotsa beers consumed.

 

Thanks, Grant. I tried topping the fluid level up and it is a little high - still have the issue. Let me give you a further insight on the gearbox issue as it is really strange, so any ideas appreciated;

..after the transmission starts slipping, turning the engine off and immediately on again will stop the slipping and the car will drive on again for a short distance until the slipping starts again….and then, you guessed it, turning the ignition off and restarting the engine immediately re-engages traction again for another few minutes…and so on…ugh

I was wondering if there is some sort of transmission pump somewhere that is struggling,…or any other ideas great-fully received?

Cheers!

 

I might be wrong, but something tells me that might be a torque converter issue....I seem to recall something similar occurring with a '72 I had ages ago.

 

Agreed.

Age is against this thing now, and service "records/memory" are long gone.

Stale fluid destroys the clutch packs, and eventually gums up the Convertor ports.

The pump is at the snout of the trans, and moves a HUGE amount of fluid at hi pressure. Never seen one go real bad.

That Trans Pump is the same design as the engine oil pump, also moves shiiit loads of oil at huge pressure, and apart from something entering it and destroying it mechanically, last a very long time.. One of mine is now at 685K kms and untouched, but on its 3rd trans (that BW12 mentioned before).

Trans filter clogged, always a thought, and that would give those symptoms. Engine OFF, gunk drops a tad, no suction of course, and away you go, and those short distance are pointing to that.

Trans Gov gear slipping, and NOW my memory faiils me 100% on the BW (TH400 I do remember and very common failure item), and that will also do what you have in a heartbeat.

 

Thanks, makes sense. I am going to drop the gearbox sump and clean (or replace?) the filter.

Will let you know how it goes but don’t hold your breath for an update as it will be on my winter project list!!

Cheers!