The X308 XJR uses the Mercedes W5A580 transmission, not the ZF 5HP24 with the weak A drum like the XJ8, the Merc tranny is quite bulletproof, so you don't have to worry about that.

The X350 uses a ZF 6HP26 transmission, which has an incredibly complex control system, would be an absolute nightmare to try and put it in an earlier car.

There are updated timing chain and tensioner kits for the 4.0L which will solve those problems, so unless you have a blown up 4.0L or are looking to make serious power with a twinscrew kit, the swap is not really necessary...

 

I totally forgot about the XJR getting the Mercedes transmission and have actually read that so sorry on that one. Yes I plan on a twin screw kit at some point and am addicted to going fast at the track of course. I know they have upgraded tensioners for the 4.0 but I like the idea of the forged crank in the 4.2 as well as the double timing chains and the extra displacement of course. I know I don't frequent here often but my v6 ford thunderbird super coupe makes 381hp and 456ft/lbs to the rear tires on 91 octane pump gas. With my new 4R70w trans and plans of e85, since I have a fuel cell and all teflon lines with an aeromotive a1000. I should be able to break mid 400hp to the tires. Anyways, my Jag will be driven until the motor lets go because in order to change the chains correctly I would want to do all of them (primaries and secondaries) as well as the water pump including dropping the pan to check for debris. I figured if I am going to do all of the work of dropping the subframe etc. at that time I would just go ahead and do the 4.2 swap and go from there on a solid foundation. I like to plan ahead, so this won't be something you see in the next few months, just trying to collect all the info ahead of time so when I try to tackle the project I won't be lost in the dark scrambling last minute to figure out what I will need. With CA having smog laws I can swap in a newer motor but everything has to go with it I can't just piece the two motors together to make it work, although, I doubt anyone would actually check it is not something I want to risk atm.

 

The 4.2 crank is not forged one. Pistons and rods are. In 4.0 engine just rods are forged.

 

Thanks I had read otherwise and it's good to know. Has anyone pushed a crank in one to it's breaking point and if so what hp levels and what type of forced induction and how many pounds of boost etc.?

Has anyone used the "ZF 6HP26 transmission, which has an incredibly complex control system" with the complete 4.2 to make this swap?

 

Not a hope in hell of making it work, stick with the Merc tranny.

 

Can't I just swap crank, rods, and pistons into a 4.0?

 

I suppose you could, but why would you bother? The idea is that if you have a dead or worn out 4.0 you can more or less drop a running 4.2 into the vehicle without the need to open the engine.

BTW both the cars you have in your profile are 4.2's already???

 

Was looking at a 98 XK8 that's why I asked

 

Just thinking out loud really, but could you fit the complete supercharger and heads from a AJ 26 4.0 SC onto a 4.2 SC block ?


They appear to share the same bore diameter, and spacing.


If so it would negate the having to re engineer the inlet manifolds etc...


Or is there a big difference in the combustion chambers that make it not feasible ?

 

The 4.3 Aston Martin v8 intake is a fit for ours too! Sometimes they pop up for cheap...

 

I bolted on all my AJ27 parts heads supercharger etc. on a 4.2 with no problems.

 

Can I ask for some details on what parts just bolted on and what needed modification?

With the AJ27 heads bolted on were you able to use all of the AJ27 timing components as well?

 

Yes I used all the 4.0 timing components as well as the oil pump. The issue I had was wanting to use my cylinder heads as they had been reworked with new cams, valve springs.

What 4.2 are going to use Jaguar or Rover?

 

I have a 01 xjr with a spun rod bearing, so looking into options. If I can just bolt on the heads and timing components that makes the 4.2 an attractive option for a short block. We will see what I can find for a reasonable price though. I imagine the rover block will have some differences.

 

I have a short block that needs new rings if you are interested.

 

I have decided to rebuild the 4.0, is that a 4.2 block that you have?

I am looking for a 4.0 connecting rod and a crank

 

It is a 4.0 short block.

 

I sure hope this works. I just ordered a 2007 XKR used motor without the supercharger and plan on swapping blower from 2001 XKR on to it. The 2001 has some serious problems with very low compression in all cylinders. Haven't found out why yet, but decided to replace the motor with 4.2 block assembly. Will be looking for help on this forum for sure. You guys are the best. thanks for all the info.. steve in cape coral, fl.

 

I am pretty sure you are going to have an issue with the intakes bolting on as the bolt pattern may be different. That was an advantage I had when using my 4.0 heads on the 4.2 block.

 

I believe Avos has adapted the AJ26/27 intake to the AJ33/34, you would have to ask him for the exact details of how it's done, I think he mentioned adaptor plates, &/or drilling & tapping new threads for the bolts. Can't be sure now.

Also your 2007 XKR engine will have VVT, not a major issue but you just need to plan for it, an external controller to run the VVT solenoids.