Pre-HE Series 3 Service Replacement - But, what is it? Relevant to XJS also ...

[wgsouter]

Hello, although supposedly fitted to a Series 3, this question is equally relevant to XJS - knowledge-wise?

Having asked JDHT and then Jaguar Classic, my engine seems to fall within a gap in records where even the Engine Serial Number is not recognised. I am hoping that the engine I have is one of the Higher (10:1) Compression Ratio Pre-HE Engines, but am currently stumped and so it seems are others; hence, can anybody out there help with details and/or identification?

The story I have is that a 1981 Series 3 had its engine replaced in 1991 with this Pre-HE (Service Replacement) where the Engine Part Number is stamped as RTC2691SR ... however, Jaguar Classic do not recognise this Part Number. Furthermore, my engine is also stamped with the Serial Number 3S1960F where Jaguar Classic again do not recognise this as a valid Serial Number - it should start with 8S apparently, but mine is most definitely 3S.

I am really trying to ascertain whether the numbers prove this engine to be a 'normal' Pre-HE or the later 10:1 Pre-HE ... it is a Pre-HE. Alternatively, I would do a compression test, but with the engine being on a pallet awaiting clean plus fit, then a little difficult. Equally, I want to make sure that I have what should have been the 10:1 Engine.

Can anybody recognise and translate the numbers?

Otherwise, I may sell this engine to buy a HE ... my Pre-HE only has 5000 miles on it in case of any interest, lol.

Many thanks in advance
Wolfie Souter
Westbury, Wiltshire

[ptjs1]

Wolfie,

A couple of thoughts:

RTC2691 is an engine block number but I'm not sure of which variant. Ignore the last suffix, Jaguar Classic should be able to tell you from which engine series an RTC2691 comes from.

I believe the XJ-S Pre-HE P-Digital block was RTC2689

The engine number definitely seems wrong, All the early V12s from the 1980 period are 7Pxxxx in an XJ12 or 8Sxxxx in an XJ-S. However, there are lots of records where V5 registration have 85 or 85- rather than 8S recorded. so I wonder if the casting digits were sometimes less than perfect. Are you absolutely sure it's not 8S...? It also seems to have one less number than expected. Again, are you sure that's an F at the end?

Cheers

Paul

[wgsouter]

Hello Paul,

Have added a pic of the numbers to show that they are all very clear - however, didn't notice until I looked at the pic in detail that there is a further number further within the V ... 16MR82 ... whatever that is ...

Regards, Wolfie

[ptjs1]

Wolfie,

I'm guessing that that this plate is merely identifying a block id. The RTC2691 relates to the block part number, SR MIGHT stand for "Service Replacement"?. The characters under it are not the engine number.

What is the engine number as identified in the engine valley by the throttle capstan?

Paul

[wgsouter]

Well ... after a bit of vigorous cleaning, the RTC Label came away (glued to the engine block) and underneath - was another Engine Number of: 8S20593HA ... picture attached ...
From what you mentioned about 8S numbers, this looks promising and I hope that it means something plus is related to whatever was done to the engine as a Service Replacement!!??

[ptjs1]

Wolfie,

That's a High compression XJ-S engine number that used "A-set" pistons. The engine number of 20593 is well into HE territory, rather than pre-HE. HE engines started at 18001, so every likelihood that this engine (before any recon / re-service was built as an XJ-S HE engine c1982.

Hope that helps.

Good luck

Paul

[wgsouter]

Thanks, but this causes me further confusion if it is allegedly a HE because the Cylinder Heads are most definitely Pre-HE with their sloping Spark Plugs, ie, front set of 3 (each bank) slope forwards and rear set of 3 backwards.

[ptjs1]

Wolfie,

The original engine number SEEMS to indicate that it sits within an engine age range that would make it an HE.

However, the RTC plate over the number number questions exactly what may have been done to recondition / rebuild the engine.

Unless you can find out the build history, perhaps from Jaguar Heritage, I think you'll have to strip / examine it to really know what you've got there.

Cheers

Paul

[wgsouter]

Hi Paul,

Yes, agree ... taken a HE Block and rebuilt as a Pre-HE ... will not know for certain until I put a camera down the cylinders plus do a compression check. JDHT unable to help as they do not recognise either Part Number (RTC) or Serial Number 3S - even though this engine is supposed to be a genuine Jaguar replacement.

Thanks, Wolfie

[poprivet]

Is there a difference between HE and Pre HE bare blocks?

Maybe the replacement engine number was intended to show that it isn't a HE engine any more. Are either of these numbers on the V5 registration document, hopefully that was updated when the engine was replaced or it might prove difficult to do now.

[wgsouter]

What I thought would be easy transpires to be difficult ... I was trying to be able to 'prove' that I had a 10:1 Compression Ratio Pre-HE Engine - as it allegedly was a Service Replacement fitted to a 1981 XJ12 Series 3.

Suppose the next step is to take cylinder pressure readings, but anybody know what a guideline pressure should be (in Bar or PSI) to determine whether the CR is 9:1 or 10:1 ?? I have seen some formulae online, but difficult to get a clear 'number' ...

Did quickly check a couple of cylinders, but my battery was only part-charged - gauge read 6 Bar, which looks awfully low. Battery being recharged ...

Again, anything constructive very much appreciated.

Regards, Wolfie
Westbury, Wilts.

[ptjs1]

Wolfie,

With the vagaries of potentially worn engine, stuck rings, unknown valve duration etc etc, I'm really not sure I'd use a cylinder compression test of giving me any confidence of a specific compression ratio?

A regards 6 bar (87 psi) , that's way too low for a good engine with rings operating correctly etc. I think you're looking closer for 220+ psi in a high-comp Jaguar V12.

If you don't want to lift the heads, I think you'd be better, confirming with camera that you've got pre-HE pistons and then using a dti or even a simple but accurate, measuring stick and manually turn the engine to measure the degree of piston movement that you get in a cycle and then try and work it out.

Cheers

Paul

[PaulGover]

I suspect the piston movement will be 70 mm, unless it's not a V12 ...