Hi fellow Jaguar fans

I'm building a racing XJS. I've just got the 6.0L engine (from a rotted out XJ12) that I want to use the bottom end of, I want to put my flat-head pre-HE heads on the top. Do I need to modify anything to do that? OR will the heads "just work"? What about the pistons? I can use the old 5.3 pistons if I need to keep the combustion chamber in the piston, assuming they're virtually the same height. I don't mind running a higher CR if necessary, as I'll be using the highest octane fuel I can get & don't mind adding boosters.

2nd question - Can I get a complete set of stud fasteners for the engine? I'm guessing a kit, if it exists, would only be available from Jaguar at £ridiculous? By complete, I mean all the bottom end studs for the main bearings, as well as the head studs. Manifold studs I can probably get anywhere & are less vital.

Basically, when I put this engine together for the final time, I want to be 100% certain I know every nut & bolt of it personally.

Cheers!
Ade.

 

here in the states, guys use a lot of the ARP fastener products, very good quality!

for engine info there is a guy in UK ,XJ5006 on this forum, he has much knowledge about such stuff.

 

Complete set of all required OEM grade studs for the top of the engine available from David Manners, not too bad price-wise. Bottom end too, but the conrod bolts are quite expensive at about 25 UKP each.

Flat heads (pre HE heads) will require pre-HE pistons as the HE head has the combustion chamber in the head. Piston height may need careful calculation to get the right compression, but I have a feeling that pre-HE pistons will just go straight in. The conrods are unchanged across all the V12 versions.

As Ronbros says, XJ5000 is the real expert and can tell you everything you need to know.

 

Thanks for the info! Unfortunately my pre-HE has one damaged piston (isn't that always the way...), I do have a spare pre-HE, so I guess that's coming apart too...

Rods- I'd assumed they'd change length otherwise the piston will come too high up the bore? I know the combustion chamber moved from the piston to the head, but it's not _that_ big surely? The pre-HE piston stops 0.160" below the deck. Based on my calculation, the increased stroke of 8.5mm (4.25mm at either end) = the piston rising 0.167" higher in the bore... which means it'll come within a gnat's **** of the head - or maybe even strike the head, depending on the head gasket. I can't believe that's the case but, if it is, then I'll need to run an extra thick head gasket to get my compression ratio back down....

 

The hole in the piston for the gudgeon pin (wrist pin in USA speak!) is not in the same place on the pre HE (flathead) and HE piston. That is how they were able to use the same conrod. As I am sure you know, the pre HE piston has a depression in the piston top which forms the combustion space, while the HE has a flat topped piston. If you go the Jaguar Classic Parts the conrod part number is RTC2997, and it is the same across all models of the V12.

Greg

 

Hi Greg,

OK - that explains it then I haven't got the 6ltr out of its donor car yet, hence not knowing that. I'd personally like to use longer rods & much lighter pistons - but money constraints put paid to that.

So.... all I need now is a replacement piston for my damaged one, and I think I'll go with a replacement head - someone (not me) dropped a washer into the cylinder & ran the engine, the piston's pretty beaten up & the head's not to pretty either. The washer, ironically, is in perfect condition!