"Non spec" can mean different things. Might be that they simply aren't the recommended brand....likely a harmless substitution. Or it could mean that they are entirely wrong in terms of heat range and reach....which might be a problem.

Cheers
DD

 

its just that some people go and buy..whatever at the parts store.

Remember the thread size and diameter on most plugs is the same, so you can put a lot of different plugs in there. It wasn't designed that way though.

Unless the manufacturer has stated otherwise, or their are proven results you want to go along with, always stick to what was in the car from the factory.

Jaguar designed the XJS to run champion XX NGK XX I dont remember which exactly but thinking you will improve your car by buying those 3 tipped ungappable iPOWER plugs or whatever it is means you believe you are smarter and know best over a large group of well educated automotive engineers.

in MOST cases, that isn't even close to true, and the car will run best if you use factory recommended replacement maintenance items. Usually even down to the tires this gets you the best results

 

Gap is important to stress and reliability. Modern engines use high energy ignition systems to fires large gapped plugs to ignite a large wave front. This puts high stress on the ignition components. Jags were not designed to support these high stresses and bits break down which causes misfires. Changing the igniting characteristics changes how it burns in the cylinder. V12 is designed for a short nose 25 thou gap.

 

not for nothing asking about sparkplugs doesn't mean you're incompetent. has anyone ever changed a sparkplug on a non untercooled buick grand national?
im pretty good at this stuff and that one plug took me 3 hours

 

The XJS help book in PDF on this forum says the replacing of spark plugs on an XJS requires several hours of labor by a mechanic. Not sure how hard it is but it sounds labor intensive just for spark plugs.

 

It ain't a stroll through the park, that's for sure.

But if you resign yourself to the inevitable and don't rush that which cannot be rushed, it isn't so bad.

My experience is that removing the stuff that's in your way actually shortens the job overall....as opposed to trying to work around it.


Cheers
DD

 

Doug is bang on as usual. Once you remove the throttle pedestal, cruise control servo, coil and a/c compressor it's a very do-able job.

 

Also, having a good beer around makes the job much easier. I don't think it's even been discussed here on the forums much which kind of beer is best for changing spark plugs. It's possibly more of a contentious issue than whether the pre-facelift or post-facelift XJS model looks better.

For my part, I like Boddington's. Just like a Jag, it fights you when you first open it, but it's so worth it once you manage to get it going.

 

Kokanee worked well for me. It's a glacier beer which helped cool my temper.

 

The right music....and a voice that could bring peace to a thermo-nuclear war.... will keep you mellow and meditative. You'll have no inclination to rush the job and bollix things up


Well, it works for me


Cheers
DD

 

Changing spark plugs in concept is not hard. Doing it on a vehicle that you have never done it on may not be hard but ketting tips on the easiest wayto do it can help a lot.
e.g.
1. Use a blower to blow out the valley of dirt and a compressor air jet to clear out the spark plug wells.
2. remove dist cap and check wires and replace and at least clean after inspecting for any cracks or arcks
3. gap plugs to 25 thou
4. While many say it is easy enough to remove the compressor, thi member found it was not necessary on his '95 if he used a 6" deep reach plug socket and an open ended wrench on the top end.
5. Photograph or label the wires if you have concerns.
6. Remember that this is two 6 cylender engines and the firing order of a 6 cylender is1-5-3-6-2-4 so if we have two and two banks it can be seen to be 1a-1b-5a-5b-3a-3b-6a-6b-2a-2b-4a-4b.
7. There are no compression washers so do not overtighten.

Or some similar guides that may educate or stimulate positive discussion.
None of us should be shamed for asking a question on tips to do a job right.

 

Bit Harsh I think! New guy-I meant new at the job of changing plugs on the V12

 

+1^

This forum is all about sharing information, which the guys do rather well IMHO.

There is nothing wrong with asking a question when faced with what looks like a daunting task for the first time.

Thanks to all the positive responders on the forum, too many to mention, but everyone knows who you are.

 

Keep plugging away Sacrider and keep asking your questions. There are more of us here that will help if we can, if nothing more than to give moral support.

Everyday is a school day and those that forget are eventually doomed to fail.

 

I agree. Looking at the beast of an engine that is the mighty V-12 for the first time feels quite intimidating! But DO NOT LET THAT FOOL YOU! One of the things I have started to appreciate about this vehicle is that it seems/feels like a lot of it was built and put together by hand. A lot of screws and bolts seem to come out with a 1/8 ratchet with very little effort, and I have to keep myself conscious of not over-tightening screws and bolts. Once you start to understand how things were probably put together and assembled, the big cat starts to feel more like a kitten than often only needs some gently coaxing to do what you need it to do.

However, like any kitten, while it wants to cuddle and purr in your lap, it also wants to bite you.

 

However, like any kitten, while it wants to cuddle and purr in your lap, it also wants to bite you.

And leave puddles of nasty fluids all over the place.

 

Awww, that's just it's way of saying "I love you".

 

Really? Not sure I want to share my adventures

 

Having just put my 89 XJS back on the road after a 10 year lay up, there is no way that I could have done so, without all the help I received from this Forum.

On 31st of October 14, I'm putting her back into Storage for the Winter but before I did so, I wanted to change the plugs.

Doug is absolutely right you mustn't rush this job, especially if you are doing this for the first time, so not being a mechanic or as skilled as a lot of these 'guys' on the Forum.

I allowed 2 days to do this Job! in the event it took me all day as if you have never done this before, it's all too easy to make a mistake which could end up 'Wrecking your engine!'

Let me explain:

Unlike most normal vehicles, the XJS uses 'Spark Plugs' which have 'Tapered Threads'

And just to make things a little bit worse, we are talking about the combo of 'Steel Spark Plugs' going into an 'Alloy Head!' so you have to be really careful and watch what you are doing.

So after blowing or vacuuming all the 'Crud' out of the way, so that nothing can drop down the hole when you take the plugs out.

The first thing I did was to put spray some WD40 around each of the plugs and then left them to soak, because when you come to unscrew them, there is albeit a very small chance, you could strip the thread in the head.

If they are seized or corroded into the holes, which probably won't happen but do bear in mind that it could, if the PO screwed them in 'Too Tight' so a sense of feel when unscrewing them is essential!

You can also risk stripping the thread in the head, when you put the new ones back, because (I repeat) these Plugs have 'Tapered Threads' so don't be 'Gung Ho' and think you are 'Home and Dry'

Put the Spark Plugs in with your fingers and make sure they screw in easily by hand, before you finally tighten them up with a Plug Spanner, as if you get one 'Cross Threaded' it's 'Game Over!'

Again as 'Doug' says do 'NOT' over Tighten them! and then you should be fine. 'Cross Threading' the Plugs when putting them back, is the 'Biggie' you need to watch out for.

As for using a 'Garage' (Please Don't get me started!) As an unskilled mechanic who is not used to working on V12's can mess this up as easily as just about anyone else , so don't be afraid to have a go yourself. It's certainly not a 'Walk in the Park' as someone already mentioned.

But nowhere near as hard as if you one day get a problem with the Brakes!

 

tapered thread or tapered seat?

never heard of a tapered thread sparkplug, but tapered seats are quite common.

in any case where sparkplug thread strip out is a possibility, following the Ford TSB
on spark plug removal on their modular V8 engines would be a good idea.

it involves soaking in penetrant, partial loosening and tightening of the plug to
smooth out the galling. rinse, lather, repeat until the plug finally comes out.