Are all 4.2L 6-cylinder engines essentially the same? By that I mean, how much can be swapped between engines? I'm trying to figure out the differences between years/generations, so if you know a good source for info without me having to ask you a lot of questions, please let me know! Also, let me know if this is not a good sub-forum for this.
Here's my dilemma, I'm wondering if I can make an '80s 4.2 look like a '60s 3.8 or 4.2. '60s blocks that I can afford tend to be stuck and too far away to evaluate or are out of my price range ($3k+)... but '70s and '80s blocks are plentiful and cheap (I found a complete, running '85 for $100). I plan on rebuilding whatever engine I get, but I'd rather start with a block in decent shape.
So, put your restoration hats aside. I know that some later engines have fuel injection, smog equipment, etc. Can I remove all of that and fit a triple intake for carbs or FI (e.g., Mangioletsi, Burlen, etc)? I know the head bolt lengths are different, but what about spacing? I know the later motors have bigger valves, so rejetting and fuel tweaking may be required. Can I fit a (more) vintage breather? I think I read that the older smooth valve covers can be modified to fit. I would also need to fit a manual trans to it (5 or 6 speed). Conversion kits tend to just say it's for a 4.2, without specifying a year. So, are all 4.2s essentially the same except for the ancillary bits?

 

With some limited knowledge, i vote yes. Buy that running 80's 4.2 Swap in the side draft carbs. swap oin the smooth valve covers.

It oughta work.

Carl

 

Yes you can mix/match pretty much any 4.2. It helps to have both engines side by side to see what needs to be transferred. Oil pan, intake, exhaust, motor mounts, oil cooler, etc. I went with mid 80’s 4.2 in my 1972 XJ6. Triple HD8s, Series I oil pan, smooth cam covers, Chevy 4 speed transmission. I kept Series III oil filter and cooler adapter. One item to be aware is different configurations at sealing rear of one of the cam covers. You will want to resolve that before installing in the car as there is limited room when installed. Easy enough to take care of though.

 

The 7L and 8L blocks, (those with the long studs), are interchangeable, because I have done it. However one thing you absolutely must check on any 7L or 8L block is cracking between the bores. These are linered engines and it is not the liners that crack but the iron of the casting in between the liners. The blocks have coolant passages machined across between the bores, and thin-wall steel liners are inserted to close these off to make the cylinder. Once the cracks are there the bridge strength of the thin material is lost so it sinks over time and the head gaskets soon fail, and will continue to fail. This happened to me and was cured with an uncracked 7L block, the original engine being a 1980 with an 8L block. The alternative, if you can't find an uncracked block is to get an engine shop to machine out the liners, cut recesses all round the tops of the cylinders, and fit lipped liners that meet and cover the cracks. Obviously this is expensive. If you do get this done, don't foget to supply the timing chain cover for the shop to bolt on before they face-off the block as the head gasket covers this too. Always check the timing chest cover for corrosion. It is possible for corrosion to create a leak between the water passage for the water pump, and the timing chest.

You haven't said what car the engine will be going into. Early short-stud engines in E-types etc may have different cast-in lugs for the engine mounts so this needs checking. Cylinder heads on the Series 3 XJ cars have the bigger inlet valves and you can revert to carbs if you want to, the earlier manifolds will just bolt straight on. You'll probably need some guidance on jet sizes, though.

 

Engines with emissions controls usually have lower compression. If you rebuild are you going to address that?

 

I'm putting a SIII engine in a SI XJ right now and everything has bolted right up so far. I swapped out the power steering mount, induction and exhaust manifolds, water pump, and crankcase snorkel. alternator/AC mount is the same through all series cars. Had to drill and tap two 1/4-28 holes in the back of the cylinder head for the throttle cable mount as those holes aren't there on a SIII engine.

If I remember correctly the early 4.2 E-types still had smooth valve covers - which should fit with no issues. As for the finned covers the only difference is the oil fill cap.

If you find a Canadian spec SIII engine like I did you will already have the higher compression engine and won't have to modify it internally.

 

I guess lower compression would mean a supercharger could be fitted. Someone asked what I was thinking of putting the engine in. Sorry, I thought I mentioned that my plan is to put it in a Mk2. I haven't found the car yet, but knowing the adaptability (and being able to work on one now) of Jag 6s opens the possibilities for a car (stuck engine, Chevy engine, etc).

 

Everything is possible, but keep in mind that the Mk2 engine bay is narrower than that of a series XJ; it also tapers in from the back to the front. The engine mounts in the Mk2 are close to the front of the block, where the alternator attaches in the XJ. The bolt holes are all present on the XJ block, but repurposed. You will need to fabricate/organise something for the generator and power steering pump. The later XJ oil filter system with horizontal filter needs to be replaced, which is easy enough. The plenum of the fuel injected engine may clash with the inner wing and firewall (and certainly with the steering column for RHD). In my opinion (not everyone agrees with me), none of these are show stoppers, but the require some thought and planning.

Supercharging: for me, any XK engine is crying out for a centrifugal supercharger. It would be perfect compensation for the lack of breathing at high revs. But, if you want to go to high revs with a 4.2, a fluid damper for the crank would be a good idea. At this point, it's all getting expensive, which kind of defeats the original objective of saving cash by using an XJ 4.2 ...

 

I forgot to mention that later 8L blocks were slotted between the bores, these being visible on the top of the block and replaced the previous machined passages . This was a spatchcock by Jaguar to try to cure the cracking problem. There was no possibility of anything really serious being done, as the XJ40 saloon with its 3.6 litre aluminium engine was on the stocks. Essentially the slotting did work, but the block material between cylinder and slot was very narrow so head gasket failures did still occur but usually not before about 80k miles.

 

the 4.2 Does not rely on a Tach Generator as the 3.8 does, so that is another issue to resolve.

I have a 4.2 planned for my 1965 S type and I am about to give up. Too many things to modify to make it fit the S type. I know many of you can do it but I can't. Maybe I should just repair the 3.8.

 

Jose,
The tach generator shouldn't be too big a problem. I've looked into it for putting the fuel injected cylinder head on my old 3.4. I haven't yet worked it all through as I've a lot of bodywork to do first. It needs a bit of electronics (and possibly a second hand movement) to resolve, but it's not difficult. The appropriate electronics depends on how you plan to manage the ignition. Some people do mechanical modifs to use the original tach generator on the end of the inlet camshaft. That's doable, but electronics is easier and cheaper. And you never have to replace/repair the expensive little generator!

 

Peter,
the XJ tach is smaller diameter than the MK-2 / S type tach.

​​​​​​the mechanicals behind the face of the gauges must be the same, but I don't know.

I had my S type clock modified by Mike Eck of www.jaguarclock.com back in 2005. Still works today. The mod he does is reversible if you ever want to go back to the original non-working clock. He does it Positive or Negative earth. The hour adjustment cable continues to work as originally designed.

Thanks for the link.

 

Jose,

We had a discussion of making a Mk2 tach work with an XJ head in January - link below.

https://www.jaguarforums.com/forum/m...around-239385/

All the Smith's devices consist of a voltmeter (aka 'the movement'). In the systems from the Mk2 and your S, it's an AC voltmeter drive by the little AC generator. The later systems monitor pulses from the ignition system and convert each pulse into a top hat. The series of top hats input to a DC voltmeter that measures the 'average' volts in. Thus, the more frequent the pulse, the more closely spaced the top hats and the meter reads higher. If the ignition pulse is from the coil, then a resistor and maybe a capacitor are are required to protect the circuitry from the high voltages. If it's from an ecu, the pulse will be more like 5 or 10V and not a problem.

With the arrangement that your ignition re-builder suggested, you could in principle use the tach from a series XJ. Since I've never seen inside one, I don't know how easy it would be to extract the internals and fit them into the case from a Mk2/S. If you can find a cheap XJ instrument on ebay or from a breaker, it may be worth having a play. There are two possible problems: the shape of the old tach as it fits around the clock and attaching the old needle to the shaft of the new(er) voltmeter.

All I've done so far is collect some info (all in the link above) and bought two old tachs, a Mk2 type from a Daimler 250 V8 and a later electronic pulse type from a 6-cylinder Rover SD1 (total cost £30). There may be almost enough there for me to make something. If not, it's have fun with soldering some electronics.

An idea that's completely off the wall: if you are going to distributor-less ignition, could you adapt the old tach generator to run off the distributor drive? It sounds a bit inconsistent adding electronics and keeping the old tach system, but I guess that's not out of order for us who run old Jaguars.

My clock hasn't worked for a long time. I'll take it apart and see what can be done. If I can repair it, I'll add some sort of protection. If I can't, I've thought of rigging up a 1.5V supply and replacing it with a quartz wrist watch movement. As usual, that's all so far in the future ... .

 

Other than the clock and the tach, what issues have you had in getting it to fit? Do you mean physically fit, or fit with existing S-Type systems (like the tach)?

 

I think the motor mounts are on different locations, the 4.2 fan and fan clutch will end up too close to radiator, I don't know if the carbs and intake manifold from the 3.8 will bolt to the 4.2, and the labor, this job is beyond my skills.