How do I decipher engine number details?

Hi,
Well, after owning my 1974 XJ6 since last June for some unknown reason I decided (finally!) to check the engine numbers. The VIN plate and original ownership papers state that the engine number is 7L82393-S.
The stamp on the LH side of the engine (passenger side as it is UK spec) by the transmission dipstick, clearly states 8L92542-H.
Obviously the engine was replaced at some stage in the past. Could anyone please give me any information on what engine I actually have?
I can’t explain why it has taken me so long to check this basic information!

Regards

Bob

Hi Bob,

Not much more than that the original XJ6 Series 2 engine was standard compression -S suffix and that the current engine started life in a Series 3 car and was / is a high compression engine, -H suffix.

That can be changed as the only difference was the piston crown shape, all XK engines have the same dome in the cylinder head. And of course a Series 3 XJ6 4.2 had a Series 3 cylinder head and an EFI inlet manifold when I think your 1974 has carbs like all Jaguars back then had, right?

Cheers!

Pekka, yes 2 SU carbs. Is it possible to say approximately what year the new engine is?

Thanks for your help, feel a little silly not having checked before :sweat_smile:

Bob

Hi Bob,

You could do searches on www.xj6data.com and see what you find. I’d guess it’s from early 1980’s.

Cheers!

Many thanks, I will check

Regards

Bob

Bob,

everything said is correct. I’m just not quite sure though whether your replacement engine really is a SIII, as 8L numbers started early during SII production run. My 1975 original engine is 8L13683. The SII parts catalogue indicates 50000s still in the range. Maybe you check eary SIII cars’ engine no. to double check.

Good luck

Jochen

1975 XJ6L 4.2 auto (UK spec)

Can you send a picture of the valley in the head? I think all S3 had the bosses for the air injection in the casting - Jochen?

… air injection …? I’m not familiar with SIII looks, but SII only have the air duct which, however, is mounted at the cam covers. In the valley there’s nothing except the spark plugs.

BTW, it might be Bob has a SIII engine with a SII (perhaps the original) head.

Best

Jochen

75 XJ6L 4.2 auto (UK spec)

Hi All, XJ6data.com had no useful information unfortunately. Here are a couple of photos of the valley


Not sure if this would assist but when the head was refurbished a few months ago, the block had the ‘cut outs’ between the cylinders. I was not expecting to see those, as I believe that they were not added as a feature until later (?) but the penny didn’t even drop then that the engine had been replaced.

It was only when I was at a car show a few weeks ago and a Jaguar ‘expert’ insisted that the engine was out of a series 1 that I thought I would verify the numbers. Obviously, the ‘expert’ was wrong!

Regards,

Bob

The expert was very wrong. Looks like a head prepared (cast bosses) for air injection which I know from the S3, and the block is slotted of course. Good engine!
I think the oil filler cap is an earlier version; the s3 had a smaller threaded hole and thus a different cap and cam cover.

Hi David,

Since I had the head rebuilt the engine is very responsive and will get you into trouble with the traffic cops very quickly! I know that these engines perhaps don’t perform as well as the modern, high HP engines but, boy this one is pretty quick!

Combined with the handling it’s just an absolute pleasure to drive. I love the sweeping bends on the back roads (where you don’t come across the boys in blue so often :crazy_face:).

Regards,

Bob

I can’t quite remember what the differences are, but an S3 is visually different externally from any other; I think it’s the size and shape of the casting plugs in the valley. Whatever, this head seems to me and my failing memory to be an earlier head. I think the S3 had those core plugs capped with a large internal hex headed plug, like a large cap screw, but the earlier ones just had a standard type external headed plug, like a bolt head. Could be wrong, however. Nice engine bay, BTW.

The later blocks had dominant ribbing on the sides.
The plugs in the valley went from internal to external hex bolts and in the end they used stamped steel core plugs. Seems like yours is not that late, maybe at an in-between stage. When did they introduce secondary air - with catalysts?

Thanks for deciphering this for me. There’s a guy on YouTube that I follow with the pressed steel core plugs, his are always leaking! Glad that I have the screwed version.

Bob!
On my 1978 XJ6L, my chassis number is on
the passenger side on the inside of the fender in
the front.
Walter

Thanks Walter, it was the approximate year of the engine that I was seeking assistance with as my engine has been replaced at some point. I do have the manufactures plate on the inside of the wing.

Many thanks for your reply,

Bob

They can be as good as those in the block if installed correctly or by the factory, but I prefer real bolts too.
The bosses are on the exhaust side of the valley.

Is the block ribbed or smooth? They also have the date stamp in the top right rear corner. For the head one can only guess I think. What matters is, it looks good! (Besides the missing lifting eyes and the loose wires)

Hi David, I attach a couple of photos of the block, it does have ribs but I’m not sure if these are what you are referring to?

I have tried to look for the date on the block but I haven’t been able to find it, is it visible with the engine in place?

There are some numbers/letters on the head, BV841.

Regards

Bob

Sorry, just realised that the photo was pretty awful, hopefully this one is a bit better,

Bob

Photo is decent enough, it is a ribbed block, so the latest and what many call the ‚best‘ 4.2 block made. The date stamp is in the bottom left corner here:


Probably hard to get to and read. This is when they cast the block, they then sat for a time to allow the internal stresses to dissipate before machining and thus they were assembled a few months later.