I have a 1998 XJR. I am planning on purchasing a donor XJ8 possibly a 2002 or 2003. I am planning on doing an engine rebuild due to the fact I have a low compression on one cylinder and I possibly have a the Nikasil liner coating. So I pretty much want to use the engine block of XJ8 and everything else from the XJR. So I would keep the original pistons and rings from the XJ8 what is the difference and would this work or not? Also I will using the original transmission from my XJR to swap over to the XJ8 motor. Thanks

 

This subject has been beat to death over the years. The amount of time and money involved to perform this sex change operation converting an XJ8 power plant into an XJR drivetrain is not an easy one. Your money will be best used into either finding a suitable replacement engine if yours isn’t repairable, have the XJR engine rebuilt or find another XJR.

 

There are ways to confirm nikasil blow by before major surgery. Can you get the head off and inspect the suspect bore? It could also dry - have you added oil to the bore? Stuck ring(s) from carbon buildup also?

 

“98Jagxjr” is simply asking whether the NA (AJ27) and SC (AJ26) engine blocks are same or not. I would also like to know and hope someone will be able to provide the info.

 

Yes

 

All the 4.0 blocks are same. I have not seen visible differences, the engine manual do not list any of them
and you can see for example here that you can use bare block for any of 4.0 variants XJ8 / XJR / XK8 / XKR

https://www.autoreservejaguar.com/ja...ed-4-0-v8.html

 

COMPRESSION RATIO!!!!!!!!!!!!!!

That is the main difference between NA and SC.

 

^
Non-mechanics question but wouldn’t compression ratio differences be managed with the heads and/or the pistons rather than the block?

 

The pistons are dished (to reduce compression) in a S/C vs flat top pistons in a N/A. If he just put the N/A engine from an XJ8 into his XJR (without doing anything to the pistons) with a blower on top with high compression, there’s going be significant detonation unless you run (for example) 100 octane unleaded fuel all the time.

 

Yes, the dished S/C pistons will have to be used, not the NA pistons. The, piston rings appear to be same.

 

When I disassembled a Nikasil piston I noticed the rings were significantly less 'springy'.
Apparently to reduce the wear on the Nikasil coating and needed less pressure to seal.

The cast iron liner blocks used rings with more pressure on the cylinder wall.

Something to consider?

 

Makes sense but the ring part numbers are same for Nikasil and cast iron liners.