Hello, I own a 1994 XJ12 with the 6.0L V12. I had a head gasket failure and after removing the heads found both head gaskets in very poor shape and a good amount of corrosion and pitting on each head including some close to the combustion chambers. The engine block seems good, it just seems the gaskets were failing for some time.
The engine has 82k miles on it but less than a 1k of those were during my ownership. It didn’t overheat while I had it, and when the gasket finally went it was a cold engine right after start up.
Anyway, I’ve taken the heads to a couple of reputable machine shops and both have suggested the pitting and corrosion is more than they can repair. Or more they want to repair and still have any confidence in their work. I’ve considered using jb weld as an option to repair the pitting and then having the heads skimmed but they also advised against that. Given the amount of work to R&R the heads I’m not sure I’m comfortable with that option anyway.
So I’m looking at options including:
-purchasing replacement heads and having the valve trains swapped over. The heads are available but expensive. The least expensive option is from SNG and whilst under the Covid lockdown they haven’t been able to get photos and confirm if the heads have the valve seats in them already or if they are true bare heads. If they don’t already have them, the seats aren’t cheap and I can’t recall if it’s the intake or exhaust seats, but one of them appear to be NLA.
-purchasing a set of used 6.0L heads I’ve come across from a wrecked 1995 XJS. They appear to be in good enough condition that taking a few thousandths of an inch off would probably suffice. Reading the parts manuals it seems the XJS had the same cams as the XJ12 up until a certain engine number, and then there is a different part number. I don’t think the seller will be able to confirm the engine number.
So would using the XJS heads seem like a good option? Would slightly different cams be an issue?
We also discovered that the plastic part of the timing chain tension was also broken into a few pieces one the heads were off. Two pieces approximately 3" long were retrieved. I’ve pulled the oil pan and didn’t find any debris in there for what it’s worth. So I’ll also have to remove the timing cover and replace the tensioner and assess the chain. There wasn’t any rattling or typical timing chain noise when the engine was running which seems strange to me.
Thanks for any input. Paul