V12 6.0 engine rebuild or not?

[Jaguar5993]

Hi,
I hope you are all well?

I have owned my 1995N XJS 6.0 V12 Coupe for 18 years now and is my 3rd V12 XJS since 1993. Always DIY.
All my cars have been fairly low mileages and my present car for me started at 37000mls and now has only 78000mls for a car that's 26 years old (with many shorter than normal oil changes.)
It is commonly known that these V12 engines, if serviced, can run high mileages without rebuilds. I haven't owned one over 78000mls.

After this summer, I am taking my car off the road to give it a long awaited rebuild and some upgrades.
Luckily, budget, time or tools are not a problem.

My main question is...At 78000mls ,as I will be having the engine out, should I leave the bottom end alone or take this opportunity to recon the bottom end?
These later 6.0 litres are tough.
My 2nd question is....I am definitely, as they say...'doing a head job' x 2 (borrowing head removal tools etc.). At this mileage, should I renew the timing chain and tensioners or leave them alone as well?
I know some might say that my questions sound a bit naïve, as I said before, I have managed to get low milers,but what mileage would you definitely refurb these engines? (ha...that's a 3rd question.)
Obviously, I might discover problems when the heads are off!
After all these years and the love of these cars...my XJS is a long-term keeper.
Any advise will be greatly appreciated.
Regards,
Nick

[davidr]

Hi Nick - if you've already pulled the engine out, had the heads off etc then it's only a small step to pop the sump off and have a look at the bottom end. These engines are relatively low stressed so the bottom ends last forever. I would be surprised if there was an issue at that low mileage unless the oil changing regime has been very poor.

[Jaguar5993]

Hi David,
Thanks for the quick reply.
Its not happening until after the summer.
If I get a chance not to rebuild the bottom end,I will leave the engine brace suspended, as I will be removing the front suspension for re-con.
I need to take the sump off anyway and renew gasket (after painting it gloss black of course.)
All the best.

[stuart1927]

Hi Nick

I see you have delayed this project anyway, but for wat it's worth!

Last year I was doing some maintenance on my 94 XJS 6L and when replacing the water pump....opened a massive can of worms!

One of the longer water pump bolts had sheared inside the timing cover. Luckily, I managed to get the timing cover off (with engine in place) and get the sheared bolt removed, but that's when things got away from me!

Getting the timing cover back on again was impossible for me with the engine in the car. People have done it, but unless you can free up enough of the sandwich plate bolts, it is extremely difficult. I was moving house during all this, so ended up having to get the car transported to an engine restorer to sort things out.

In a way this was a blessing as when they took the engine out (needed to as I'd damaged the gaskets) and started to look at things, it turns out the timing chain tensioners were cracked and there was a lot of corrosion on the cylinder heads that needed sorting. In the end, a huge amount of work and expense resulting in effectively an engine re-build. A lot of wiring issues to fix as well.

Looking back, I think the previous owner had run the car with a coolant leak (water pump broken bolt was likely long term) and this led to a number of knock on effects.

If I was ever doing anything with one of these engines and you have the ability to remove the engine from the car....I'd do it. That way you can replace a lot of things so much more easily, including bottom end gaskets and timing cover gaskets. Taking care of these items with the engine out is really easy.....with the engine in....horrible. I aged 10 years trying it!

It may be different for you as you've had your car a long time and know the history. My car looked and drove very well, so I really didn't expect the problems that were uncovered.


Best of luck

sbb

[Jaguar5993]

Hi Stuart,
Thanks for your reply.
Yes...often simple things can turn into a nightmare!
I’m actually looking forward to taking the engine out, as you said …it’s easier to work on naturally.
I too could find a horror story, even at 78000 miles.
The timing to get this long project started was down to now, the build up of other things to sort out with it and the ending of tax, MOT and insurance timing etc.
Off topic, but I have really noticed how nice and different these cars look on our roads today..as they say...’a head turner’.Definitely changed over the past 19 years that I have owned the car.
Thanks again.