Jaguar 4.2-6 question



I am looking for a bit of info on the Jaguar 4.2l DOHC six. Primarily, I need to know what the bore size and spacing is. Anybody know where I can find this, or have the info themselves?

Thought some Jag fanatic would answer this one, but Jack is away!

I know very little about Aristicratic English Grunters, sorry. The 4.2's cylinders were pitched differently to the 2.8/3.4/3.8 engines to stop cylinder head gaskets blowing. It's likely the spacings are similar to the 4.045 inch Ford I6. Studs and water passages are going to be very different. And the wide angle hemi head with just two valves per cylinder is not like the pent roof 24 valve Barra 182/240 DOHC Falcon head in flow or performance.

Remember too that the Jag XK engine had a similar hard block dimensions as the early Standard engines used in the pre-WW2 Jag SS90 and SS100 sports cars. And they had narrow bore spacings.

Lots of good fortune on this one bro'.
I'm still looking through my Jag books, but I haven't touched a Jag since I went to the academy (except to drive 'em!)...getting on toward 8 years now...most of those were the 120/140/150/E-types.
You can find a lot of info by surfing thru the site.

The 4.2 used the same gaskets and bolt pattern as the earlier 2.4/3.4/3.8 but with the cylinder cores shifted slightly to allow for a bigger bore, but the head layout was basically unchanged from earlier models. The spacing change was deemed insignificant enough to warrant a like movement of the combustion chamber.
I got out my Jag factory manual to try and help. I found the bore on the 3.4 L listed as 83.0mm =3.2677in, the 4.2 L is listed at 92.07mm=3.625in.
I could not find anything on the Bore center spacing or crankshaft rod bearing spacing that would help on the cylinder spacing. The above mentioned site would be a good source for the information you are requesting.
What are you trying to do with a Jag head or block?
Specifically, I am looking for a DOHC head with a 4" bore, or close to that. I need a pattern for a 300-6 DOHC. I know that the newer 4.0's have a smaller bore, but none of my service lit had the pertinent engine info, just engine management systems.

1.The grand pappy axe 144 thru to 200/250/3.9 SOHC/4.0 DOHC I6's Ford engines are 4.045 centre to centre bore spacings. The 240/300 is 4.4", following on from the Y/I-block ancestory that runs through these engines.

2. The Aussie Duggan heads for Chevy 230/250 L6's were the same 4.4" bore spacing, I think, but only SOHC. So was the Aussie Chrylser 215/245/265 Hemi , but it is an OHV head.

3.There are some US SOHC heads...the Pontiac 230/250's of course.

4.The Jag engine is more Falcon 144-200/250 size in its bore spacings. 4.2 is the raggard edge for capacity of this fine piece of work. The block is massively deap at 11 inches (one inch taller than yours), with 1.7 inch tall pistons, and massive 7 inch long rods that allow this oversquare beast to pull well past 5000 rpm with distain.

5.The Renault Torino ran the old SOHC Kaiser engine in a Rambler/AMC body until the early 1980's. It was hugely undersquare!This engine was similar to the old Continental engines in topography/architecture.

6.The later Landcruiser had a 4.5 liter DOHC I6, before the current Lexus 4.7 liter V8. But I'm not sure of the bore spacings. They may be just based on the Supra I6 DOHC cooling. Toyota loves to rationalize its engines, just like Ford does. The Diesel variants of this engine are related too, I think.

7.For the 300 I6, your best option is looking for

a)an OHV valve Cleveland style SVO A3 head and cut it up. They have a 4.375" centre spacing bore, but I've heard some intrepid Americans have done this using Cast Iron heads.

b)The other option is grabbing the 3.8 Lincoln/Mustang/Taurus v-6 heads and then co-join them. Check out bigger diesel sixes, and see that some of these had heads that weren't cast with all chambers together. So the idea isn't just a dumb a$$. The head gasket issues with this engine were not realted to the castings.

c) Another option is the SCAT V4 Chevy based engines used in some TQ or Speedway classes. You could grab three heads, and have a go.

8. The Aston Martin DB4/5/6/S had a square 92X92 mm engine. This may have a similar bore spacing, but it was only a 2-valve DOHC head

Sounds mighty expensive, don't it?

Heaps of fortune!
Simple suggestion,
Look at a modern DOHC in US production, we are Ford freaks so let's say Ford.
Pick the best design DOHC Ford builds, or even SOHC if you decide to make it a little simpler. Design yours around their existing parts and pieces, would cut down on speciality items. Use Ford lash cups, cam followers- rockers, Valves, spring retainers, keepers, drive wheels, etc. Could even mix and match to some degree. But the more off the shelf items the easier and cheaper. Pick one being raced, then there would be after market performance item for stepping up.
Physically both Jag inline sixes are huge engines. The 4.0 AJ16 24 valve engine in my current XJ6 is massive and dwarfs a 200 engine. It is physically much larger than a 300. The XK series engine that was produced from 1949 onward is larger still.

Also, bear in mind that if you are thinking of trying to use an XK head as a model for a 300 DOHC design, by modern standards it is not very efficient. Even in 1949 it was not technologically cutting edge. The 4 valve designs common to most DOHC engines today are far superior in combustion efficiency.

I would look instead at the Toyotoa DOHC inlines as models. The 5M-GE, the 7M-GE, and the 5FGE are much better designs than the Jag.
Thank you all for your suggestions. For the immediete future, I am doing an SOHC, using a stock head with SBC valves, and a cam carrier on top, similar to Subaru's design. I am designing my 300-6TT intake to clear this setup, which will be about 1/2" taller than a stock carb valve cover. I have the Subaru heads as well, and may copy their combustion chamber design to a certain extent, possibly with the combined intake runners. Two valves are a viable alternative, they aren't dead yet, and still flow much better than a stock u-turn head. While I am doing this to satisfy my own curiousity, I do have to wonder if these would be a salable item; is there enough desire for something like this that people would pay for essentially handmade custom cylinder heads? I know the SOHC conversion would be viable, but DOHC, or an all-out crossflow?

Dunno if this helps on the bore centres issue on a head your not likely to use anyway, but here goes...

More info to confirm the XK 6 Jag engine was Standard based. From this web site, historical drag racing in Europe

The TR2 power unit now sported a grafted-on double OHC Jaguar head minus the front and rear combustion chambers and valve gear.

This links Triumphs Standard Four-cylinder to the XK6. Remember that the first 3442 cc DOHC cam had almost the same bore and stroke dimesions and size as the Jag SS100