Hello Gentlemen,

This is my very first thread on Jaguar Forums. I have been lurking around here for days researching and I have learned a lot new stuff here.

So, to my problem/question.

I bought a 2000 XJR with the Nikasil "defect" as a project car. The car was made in May of 2000....so close to August (the cut off for Nikasil)

After researching on Jaguar Forums I have found the thread "converting 4.0 to 4.2" and I love it.

To buy or even to find a 4.2 supercharged engine in Canada is nearly impossible and not very cheap, but I have found a lot of 4.2 NA engines for 1/3 of the price.

So I was thinking to buy a newer 4.2 NA engine, swap the pistons to lower the compression and that would give me what I need.

Would I need to change the heads as well? If so, can I re-use the ones from the 2000 4.0?

Or, can I just use "thicker" gaskets under the heads to lower the compression?

Please let me know what you guys think.

Or if you have 4.2 supercharged engine for sale, let me know as well. LOL

{If I have missed a thread explaining this, I apologize and please point me to it}

 

The main diffrences between NA and SC 4.2 engines are:
-oil jets for pistons cooling on an SC engines. I can't tell if it is possible to add them on a NA engine
-VVT on an NA engines, you'll need to block the oil passages
-different pistons

It is possible to use the heads from AJ26/AJ27
Thicker head gaskets are a bad idea. They should be way to thick and there's a risk of head gasket failure.
Also you can search a 4.2SC engine from a RangeRover or RangeRover Sport. They are all the same, except an oil pan (you can install an oil pan from a 4.0 engine)

 

Thank you MoscowLeaper for your response. I will look at the oil jets issue right now.

 

Trade it in for an R....... It's cheaper

 

He's already a XJR owner. Just some nikasil issues and he can't find a used SC engine.

 

I understand now....... So you want to use a block from the N/A to fix a supercharged....... I can't see how that would be a problem, you would have to swap everything over however it will be a bit more complicated using a 4.2 as you mentioned the pistons, you would have to get the supercharged ones. You could use your heads, Avos will be the guy to ask for sure, it would only be the oil ways I would worry about

I stroked my nikasil 4.0 XKR to a 4.2, using the crank rods and pistons from a N/A I did cheat a bit and machined the tops of the pistons, they haven't blown up yet but let's just say I wouldn't recommend it, it was a suck it and see exercise

 

The pistons of the 4.2 SC are forged, and another benefit are the oil jets under the pistons for the 4.2, and ideally you should use the 4.2 heads, as the pistons shape fit the heads the best.

Now you could use your 4.0 heads, that would lower the compression as the chambers are bigger in size, and probably compensate for the 4.2 NA pistons, so you end up closer to a 9.1 compression ratio, even with the stock 4.2 MLS gaskets (do use these!). This would be the cheapest solution, but not the best, and I can't guarantee anything...