[v12-engine] Cost of a rebuild

OK I don’t know, I have sets of bearings, gaskets, etc. sitting
here that I bought at wholesale decades ago…

However I’ve probably been inside a lot more V12’s than most
people here…
Unless you know something horrible happened (in which case buy a
whole new (used) engine {I pay $250 for one} and rebuild that), In
all likelyhood all you really need to do is buy rings, bearings,
gaskets, timing chain, and do a valve job… Maybe about $1000?
Chime in anyone who’s bought parts recently.
That’s on the majority of motors I’ve taken apart with up to
about 150,000 miles.
No need to plan boring or grinding the crankshaft or any of that
The stress on a V12 is TINY compared to most engines… with
2.88 rear end ratio’s the engine is just loafing along. Nearly
every V12 has an automatic which sole purpose as far as I can
determine is to take it easy on the engine and keep it from working
Aside from that the motor is built massively too stout!
Connecting rod bearings that are 2.3 inches compared to about 1/2
that on any rod near it’s size and stroke. Main Bearings? Giant
oversized heavy duty! At red line the piston is just loafing along
compared to say a Chevy/Ford etc.!
Bottom line? If the engine needs a rebuild and nothing major is
wrong ,budget somewhere around a grand and you should have a good
The timing chain tensioner is one of those Iffy things…
Oil chenge on schedule? good oil used? OK here’s a case where
judgement is needed… I’ve reused most because I know that by the
time the chain actually wears through there is a good chance the
car will be in the scrap yard… Here’s a guide for judgement. How
deep are the groves, (roughly) 1/3 of the way worn through? It’s
got 100,000+ miles on it? So somewhere around 300,000 miles it will
finally wear through… (by then gas will cost 47.50 a gallon

I have replaced some that are deeply grooved and also replaced the
chain guides… That’s one of those deals where maybe someone lied
and the oil wasn’t changed regularly, or the chain not installed
properly after a blown headgasket or dropped valve…
If you’re one of those who have a dropped valve engine, buy a used
engine for parts… It’s cheaper than buyng the parts and why have a
couple of brand new valves, piston and liner on a used engine? OK
feeling generous? Throw a fresh set of rings in, maybe bearings…
(you’ll need gskets anyway)…
Rather than buy a lot of new parts you won’t need. Borrow or buy
a set of accurite measuring tools…Then when you put the engine
back together you can feel confident in your work.–
Wayzata Minnesota, United States
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Thanks for this post. I own a 1985 XJS v12 HE…It has 97,000 miles. Thinking of getting the engine rehabilitated before i get it painted. It has a bad oil leak and it doesnt seem to be running at full strength like it should…My father was the original owner. The car was garaged and is in great shape, feel the need to preserve it.

Eric Sheaffer


a full rebuild can cost around $10K, check it out closely , may not be anything serious!

as MG said they rarely wear out, usually some minor part is out of order!


Hello Friend, Thank you for the helpful response. I agree, perhaps things are not as bad as I think they are…Also, 10k is a big number.
Do you own a jag XJS?

Best, Eric Sheaffer

We own and drive five Jaguar’s, the sixth is a 1957 MK VIII that is still a major restoration project in work

We have two V12 Jaguars, a Signal Red Classic Collection XJ-S convertible and a 1990 Series III XJ12.

I have done most of the servicing, repairs and restoration of these six Jaguars over the past 18 years. I don’t do body work or paint, but pretty much everything else.


I’ve never rebuilt an engine without doing pistons.

Machine work, what are you doing? Very rare that it’s “fine”.

Boring, decking a block, crank and rod work.

I own an XJS and a XJ12C. If the XJS needed a rebuild, another engine would be sourced. The 12C, likely to get rebuilt.

Had about $6K into the last XK engine and I did the assembly.

$1K? For the amount of labor that is going to occur, I think you are taking more than a few chances that will cost more later.

You seem to be looking for confirmation, not advice, good luck!

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yes ,pic


Wow, what a looker…love the vintage side pipes, i bet that sounds awesome… Please share more!
I wish i lived near you, i would pay you generous amounts of cash to fix/rejuvenate my car. My residence is Hanover Pa.
My father owns the xk8/R

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You have a handful of beauties…well done! Would love to see some pics…
Here is my car

I’ve owned around 50 Jaguar V12’s over the many decades I’ve been involved with racing Jaguars. I’ve never found a need to replace pistons unless I’m building one with oversized bore and high compression. Or oversized bore, high compression and longer stroke.
Carefully measuring wear on stock pistons I’ve never found them out of tolerance and that includes some very high mileage engines. With two exceptions. One the previous owner had not properly tightened the oil filter and ran it without oil until a con rod vacated the block. The other leaves and debris between the A/C and radiator blocked air passage into the radiator and it swallowed a valve.

If you feel compelled to replace pistons, that’s OK everybody has their way. I feel secure in close examination of parts and reuse if in tolerance. I’ve built up enough inventory of used pistons That I can follow the Jaguar factories policy of batch mixing to obtain optimum performance.
The Jaguar factory held pistons to a 2 grams tolerance specification however I’ve pulled virgin engines apart and found tolerance of up to 3&1/2 grams. By batch mixing I’ve been able to get tolerance much closer than the factory.
As for machine work. Even engines that will be raced at RPM exceeding 8000 I rarely find the justification to do much if any machine work on other than balancing. Decking, lineboring, etc all tend to take the engine away from stock specifications and as a result add complexities to final assembly.

It’s not that I’ve never seen areas that are less than perfect, it’s that usually the correction will create more issues than it repairs. This is not a simple pushrod engine. As an overhead camshaft engine decking the block, surfacing the head, moves the camshaft closer to the crankshaft and loosens the timing chain. While that too can be dealt with the real questions is it worth it?
Even for the factory judgement was called for and with the tiny production of V12’s some years clearly some compromises were made.


To completely be fair when a racing engine calls for it I do not always use Jaguar parts. The connecting rods are too heavy but perfect for longevity. I will offset grind the crankshaft to gain stroke, and the foctory head gaskets leave a great deal to be desired.
When I ported heads I used to use my vertical mill to get the intake ports opened up and flowing to their full potential. The exhaust ports already flow too well. Normal relationship with the intake is 80% and the factory has them flowing at over 90%. So it doesn’t take much time to do the exhaust ports once you’ve got the intake ports flowing properly.

The stock valves are really nice pieces but if you are willing to sacrifice bottom end power for peak power bigger valves are called for. Rob Beere has off the shelf ones that are better but all out you can use modified 2 inch Chevy ones for the intake. They offer about 18 more horsepower over the Rob Beere ones but only above 7300 RPM. Plus I have no idea how reliable they are since I sold that engine and haven’t heard about it since.


Your XJ-S coupe is stunning. You should keep it looking and running it’s best, but you alreasy know that. :wink:
I have been a member of Jag-Lovers since 2000 when I got my 1984 XJ6 Vanden Plas and the XJ-S list since I bought my wife a 1990 XJ-S convertible. I have learned a lot about our six Jaguars through Jag-Lovers and members have helped me immensely with a lot the servicing, repairs, and restoration challenges that I have faced over the past 18 years.
Here are two pictures of my wife’s 1990 Signal Red Classic Collection XJ-S convertible. The first is after the repaint and right after a friend and I installed a new convertible top ( a first for both of us). The second was taken after I completed an engine bay restoration last year. The car has 128K miles on it now and is driven almost daily here all year long in our San Diego area location.


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Ronbros is right, chances are if the performance is off it’s more likely to do with the tune or operating condition than anything mechanical.
An oil leak even serious one is probably a seal or gasket. Rather than anything requiring a complete overhaul. Often a shop will suggest more work then is actually needed. In part it’s to cover their butt in case they miss something and have to pull the engine again. In part it may be because they need or want the added revenue. And Frankly it may be because they just want to see what a V12 looks like. They aren’t ordinary and I remember how much pleasure I got from doing my first one.

One data point: about 3 years ago I had my heads rebuilt. Total cost was about $8k, including parts and labor. But, from you’ve said there might not be anything so serious. More likely the poor running is due to fueling or ignition issues. Oil leakage is probably cam cover gaskets.

Thanks for your input…
I am jealous about the XJ12C. What color is yours?

When I tidied up the engine bay of my wife’s XJ-S convertible last year I removed and replaced ALL of the belts and hoses. I found that the oil cooler and transmission fluid cooler hoses were oozing fluid right through the hoses, and the oozing fluids were driven by the wind and gravity across the bottom of the engine bay and the bottom of the car over time. I couldn’t find new ones at the time so I took the old ones off the car to a local shop that rebuilds hoses using the original metal fittings but with new modern hose material. Those four rebuilt hoses remain leak free eliminating four source of fluid leaks. In addition the new cam cover gaskets and copper banjo bolt washers have resulted in a very clean and almost leak free car. I say almost because the transmission pan seal is leaking again. I removed and replaced it a while ago, but it is leaking again. This is one PITA job that I am not looking forward to doing again, but I will have to again soon unfortunately due to the messy drip pan that I have to clean on a regular basis. :frowning:


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Thanks for the encouragement! Mine still drips. What worries me is the driveway since we had it redone with pavers when we redid our landscaping 3 years ago.

While the head work was being done I had them R/R the pan and all the oil filter etc., and of course the cam covers and related. consequently, the engine was leak free for awhile. But last time it was on the lift the tech pointed out oil dripping off the bellhousing lip. He believes it’s the rear main seal, but I’m not so sure because he didn’t look carefully upward to see where it was coming from.

But the real nuisances are the transmission and the differential. Both have been resealed but it didn’t last long.

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HI MG, my valves are from Lanky GRP44 25 yrs ago, they are single piece FORGED Stainless steel.

3MM oversize inlets, 2MM oversize exhausts, no problems with them.

ERIC some pix of inside my engine V12 .


sorry for the 25yr old pic resolution, cameras have come a long way since.
also had my XJS weighed ,comes in at 3400lbs, YUP weight is the enemy of performance car.
MG you may notice the different shape of bowl in piston,vs the factory cast pistons, the curved round bowl seems to be the accepted shape nowadays!!


O car’s weight down to 3400 pounds? That’s good. If I remember you still have A/C and I assume a few other civilities to deal with Texas weather.

I’ve had The XJS down to 2700 and I’m sure if pushed there is at least 200 more pounds to loose. I wish I hadn’t tossed those splash molds awayI bet I could have gotten at least 2 more sets out of themjk