For those youngsters unfamiliar with the venerable engine used by Jaguar for 40 years, here are a few notes.

1. XK engine announced and installed in the XK120 sports car in 1947. Engine is 3.4 litres and is later put into the Mk VII saloon (subsequently VIII and IX).
2. 2.4 litre short block version developed for installation in the small saloon (sometimes called the Mark 1) in 1955. (later these cars got the 3.4 as well as the small version was not powerful enough for the US market)
3. 3.8 litre version developed (with the 3.4 and 2.4 carrying on in production.).
4. 4.2 litre version developed to increase torque. This engine, like the others, had short head studs secured to the top deck of the block.
5. Block is then redesigned for the 4.2 litre engines with long head studs passing through the top of the block into the bottom of the water jacket. These blocks are called the 7L type. (L for Long Stud). Reason for redesign is to strengthen the engine
6. 7L block changed again to become the 8L block, but not much different; it still has the long studs

(Note the use of studs, whereas US practice was, and is, to use bolts for securing the head).

Cylinder heads (aluminium), changed quite a bit with A and B type heads, straight port heads, etc. Key thing is that block size remained unchanged to allow the various engine sizes to fit the tooling as Jaguar had little money for factory equipment; the company was run on a shoe string.

1970 -Large sums spent on mechanised tooling for the new V12, but the 6s carried on with the old tools. Much selective assembly was needed to get a reasonably good 6 cylinder engine. Oil crisis of the 70s meant the V12 did not sell very well, so the 6 soldiered on.

Key fact to remember is that the late 4.2 engines with the 7L and 8L blocks are seriously flawed and crack between bores 1-2, 2-3, 4-5 and 5-6. Not only this, but the very long headstuds, being bathed in coolant for part of their length corrode and fail.

The reason the 4.2 cracking occurs is because Jaguar had to siamese the bores into two groups of 3 to fit them into the block length. This meant no coolant passages between 1-2, 2-3, 4-5 and 5-6. To get round this, Jaguar machined passages between these bores using the bore itself as the entry point for the tool. So each bore ended up looking like a 2-stroke engine. So to finish the job, thin-wall liners were pressed in to cover them up. The trouble is that this machining now left thin bridges of metal at the top of the block between the bores above the new coolant passage. Over time with the new engine as it heated up and cooled down, cracks developed in these bridges which eventually crept up to the top of the block. All the bridge strength disappeared, and the surface sank slightly, taking the pressure off the head gasket which promptly started leaking allowing combustion gas pressure to enter the cooling jacket and cause havoc. The only remedy for this cracking is to machine out the liners, machine recesses in the block deck and fit "top-hat" liners that have a lip to cover the crack, an expensive job.

Very late on, Jaguar must have got a guilty conscience, and re-hashed the coolant passage machining by ceasing to use liners, and cutting a thin slot into the top of the block between each bore until it entered the coolant gallery on each side. These blocks don't crack, but the head gaskets can still fail albeit at longer intervals.

The other thing to say is that when the engine started its production life, it was very durable by the standards of the day, but eventually could not keep pace with peoples desire to do pan-galactic mileages in their cars. Hence the all-aluminium AJ-6 and AJ-16 engines which are reputedly bullet-proof, far more so than the later V8 which gave so much grief to its owners.

My opinion is that the X300 6s were the best cars Jaguar ever produced bar none, (they had the curves back unlike the awful squared-off XJ40s. They would last for ever if it were not for rust, that perennial bugbear of all Jaguars.

 

good history lesson!

 

A couple of questions...

1. Can you give some idea of when the various changes to the XK engine came about (i.e. which later engines are good or bad)?

2. Can you be more specific about the "grief" people got from the V8 engine and what, if anything, can be done to avoid it?

 

Hi Jgwynne

The XK 4.2 engine was altered to long head studs in the very late 60s when the XJ saloon came out. Up to that time it had short studs. The long stud engine number includes the letter 'L', normally 7L and 8L. The 8L block continued until the end, but in the last few years of production the coolant passage was changed to slots as I described. This was around 1982, but may be later. This cured the cracking problem.

The really old engines like the original 3.4 and 3.8 are OK, (but there are not many around now), but note that there was a modern 3.4 litre engine using the long stud block, but this was not exported to the US. This did not suffer block cracking due to the smaller bores resulting in less stress in the engine.

As for the AJ-V8, judging by the posts I see on the forums and also letters and technical articles etc in the UK Jaguar Enthusiasts Club magazine, only engines from around 2002 are really dependable and the 4.2 the most dependable of all with virtually all serious issues dealt with. Before then, there was the Nikasil issue up to 2000, and also the camchain tensioner issue which lasted into 2001. This latter problem is easily sorted out provided it is caught before failure.

Like a lot of manufacturers, Jaguar use a lot of plastic components around the engine, one of which is the thermostat housing. These can crack and leak, although I understand this issue has also now been dealt with.

Basically, we all expect cars to go to Mars and back with little attention so as an "old codger" who remembers cars being fit only for scrap at 45k, the modern cars are incredible. The only trouble is that they last well, and due to depreciation are cheap when a few years old, but maintenance and parts are the same as when the cars are new.

 

Thanks for the info. I've always liked the looks of the Series III XJs and always kinda wanted one. I understand there are some issues with some of the oil seals and that people who run a S3 are better served by using non-factory replacement parts for those seals as well as the suspension bushings. From what you're saying, the XK engines used in the later incarnations of the S3 should be pretty sound. Is that fair to say? I figured that it would be safest to try to find a sound one from 1986 or 1987.

What's your view on the V12 engine? I test-drove an X308 model once and it seemed to be pretty much like the 1995 XJR in terms of power and performance - though with a slightly different character (a little less power at low revs but more eager to rev than the blown six)

Everything I've heard about the 6 liter V12 is that it is pretty robust if it has been cared for properly.

I've got a 2000 XK8 convertible now that has just hit 90,000 miles. It has been reliable (apart from the problem with the top that I had and I also had the problem with the cracked thermostat housing).

 

Hope you don't mind me jumping in.

I think the '86-'87 Ser IIIs are the cream of the crop due to detail changes in the car itself but, actually, the last 2-3 years of 4.2 engine production were known to have issues, presumably due to elderly tooling that Jaguar had no intention of renewing that late in the game.

By now, though, any '86-'87 you're considering has stood the test of time, as any manufacturing issues would have been corrected earlier in the life of the car or relegated it to the scrapyard years ago.

One important factor, often missed, in 4.2 oil leaks is to keep the breather system clean. This won't fix a leaky seal, of course, but it sure can minimize the severity of the leak.





I think they are fabulous and darn near bullet-proof. The only thing that'll hurt one, it seems, is overeheating.





Agreed.





Yes, and quite gutsy, too.

Cheers
DD

 

Hi Jgwynne

Can I suggest you read-up as much as you can on these cars, and try to buy a few books on the model, (made from 1968-1986 in the UK). There is a book by Nigel Thorley dedicated to these saloons.

If you are moving out from considering the engine to the rest of the car, then there is an awful lot of things that you might have to do, (assuming you buy one). Lots depends on how diligent the previous owners were in maintaining the car. Remember, the youngest car you can possibly buy will be 25 years old.

The XK engine was designed during World War II and the bottom end is typical of pre-war engines, although it had a very modern (for 1947) OHC cylinder head. The one thing Jaguar never altered was the rear main oil seal on the crankshaft. This seal traditionally leaks even when new and there is nothiing you can do about it, except park the car on a forward slope so the oil doesnt bathe the seal whilst the car is standing.

Being originally designed in the mid sixties, (I remember them being on show at the London Motor Show in, I think, 1967), the car is a child of its time, so was designed for repairability by skilled mechanics. There were no electronics on the Series 1 and 2, and only the fuel injection on the Series 3 is electronic, and even then, it is analogue, not digital.
There is nothing "throwaway" about this car. So you will find almost anything can be fixed if you have the time, the tools and the patience. Parts are generally not a problem except maybe for trim and body panels.
You will probably have to get some stuff from UK suppliers as well as US, now no problem with the internet.

Paintwork is a particular pain in the **se with the Series 3s because British Leyland, who owned Jaguar at the time they came out, decided to install a new paint system at the Castle Bromwich, Birmingham factory called TPA (Thermoplastic Acrylic). This was an abolute disaster, and if your car needs respraying, it will only work if all paint is removed back to bare steel as TPA will not accept overcoating. By the way, TPA is now no more, it was replaced shortly after the XJ40 model came out.

I had one of these cars for 14 years and did almost everything there was to do in that time !! They are really lovely to drive, and the term "Magic Carpet" must have been invented for them.

 

Thanks for the flashback ; The XK engine is one of the great engines of history, it has an incredible racing pedigree, it is still accessible to the home mechanic and offers a wide array of parts interchangeability which allow easy upgrading.
And that growl is unmistakeable and irreplaceable.
IMHO. Best regards
Francis

 

I have a question I have a 52 xk120 3.4 litre engine and When i got it 8 years ago (i was young) i tore it apart. iv moved and lost some parts, like oil pan, nuts, bolts. Now im lost, If i buy a 4.2 litre engine will I be able to interchange parts? and will it be a good guide?

 

Regarding interchangeability of a '52 3.4 litre engine out of an XK120, and the later 4.2, there was much commonality at the beginning, especially the cylinder head. As time went on and modifications were made, this became less and less. The oil sump bolt pattern and shape remained the same throughout, but sump shapes were made to match models.

Best to try finding another 3.4 up to around 1968 from a Mark 2 or S-type, or maybe an early 4.2.

 

I love learning from you guys. Thanks.

(for info, I uploaded the XK engine info' into 'Other Jaguar Models' FAQ)

 

Sorry to revive an old thread But am I correct in what I've read that the e-type 4.2 had a higher compression rating than in the 4.2 found in the XJ6? And if that is the case, could the 4.2 EFI engine handle the higher compression rating?

thanks for your help

 

The E-type 4.2s were made with 8.0:1 compression ratio or 9.0:1 compression ratio depending on year, market, owner preference, and emission requirements.

The 4.2 EFI was also built with either 8.0:1 or 9.0:1 compression ratios. Or, according to some spec sheets, 7.8:1 and 9:0:1

So, yes, the 4.2 EFI can handle the same compression ratios as the 4.2 carburetted engine used in the E-types

Cheers
DD

 

Hey! My mame is Andres Zamora. I live in Bolivia. I'm currently restoring an old 69' E-type I got from my grandfather. I do not have its original engine, I'm In the look for one. Since being in Bolivia makes it harder for me to find an original E-type engine, I bought a 4.2 XK6 engine of the XJ6 '79. My question is the following. Is this engine full compatible with my E-type? My mechanic told me it' to big and it doesn't fit. Thanks!

 

It's nothing like it.

 

Dream would be to bring some small updates to the classic XK DOHC. I would love to try to build one with modernized CFD driven porting techniques and a twin plug cylinder head- driving the compression ratio higher.
I would probably just pick a motronic fuel injection system off of a contemporary car, like a BMW M88 from an M635CSi (motronic 1.1). Would be fun.