6.0L V12 cylinder head repair/replace options

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

I am looking at the JDHT website and see that the XJS and XJ12 had the same part numbers EBC10530 and EBC10531. Here is the link:

https://parts.jaguarlandroverclassic.com/ebc10530-cylinder-head.html?code=910122106423

It is listed as NLA. Unless SNG has NOS heads, I think you should go for the used ones from the XJS.

Good luck!

on different engines (Rover 4 cylinders, reworked head) , I’ve seen some aluminium welding done to the pitted area, then skimming back to flat
the workshop doing the welding was also doing the skimming, so may be worth asking around ?

Thank you. Yes, the cylinder heads are the same, it was just the camshafts for the XJS that may differ from the XJ12. I don’t have an XJS parts manual so I looked it up on SNG’s website and they show a few different part numbers for the XJS 6.0L camshafts with the change occurring at certain engine numbers. Perhaps they are just superseding part numbers without any actual change though. The JDHT diagram doesn’t reference different engine numbers.

https://parts.jaguarlandroverclassic.com/parts/index/part/id/C03.910.91012.91012206.910122063831/brand/jaguar/

Regarding XJ12 cams… the late XJ12 had Nippondenso coil pack ignition, so one of the cams ended up with a peg and a sensor stuck in the cam cover (pass side USA) I don’t think the XJS ever got the cam sensor, because it definitely didn’t get the nippondenso system.

If you’re looking for 6.0litre heads. Contact Building the legend I think they have some.
Contact Neville Swales - a long-standing forum members.

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I have a 1994 XJS 6 Litre engine and gearbox for sale. It’s a Marelli like yours.

I had an advert here, but I can’t find it now. Maybe it’s too old.

I may be too far away, in NIagara Falls/Buffalo Canada area.

I was hoping to sell the whole engine, but maybe I could remove the heads and ship.

PM leatheriquecanadacomputan.on.ca

Rob

Hello, thanks everyone for your input and replies. I haven’t had any time to really proceed further so still looking at my options. I’ve corresponded with Neville Swales and he does have some used 6.0L heads available.

@xjsv12coupe, a welding repair was my first thought when I saw the condition of the heads and I did discuss that idea with a couple of machine shop owners. One said they didn’t think the repairs would last, said they tend to ‘bubble up again’ after some time, the other shop also was hesitant about the welding approach working but also thought the labor costs would justify the approach of just buying replacement heads. I plan to revisit the welding repair idea with the 2nd shop.

If I do use a set of heads from another XJ12 or XJS, what other work should I expect to undertake beyond machining them or a skim to make sure they are flat? Adjusting the valve lash? Removing the camshaft to see if it’s straight also? Robert, I believe we spoke on the phone previously about the engine you have. I’ll send you a pm. Thanks.

Ive welded up hundreds of XK heads, and more than a few Rover P6 heads, and none ever failed.

I just ordered a set from SNG and the have new valve seats and guides already installed

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I can get pictures if you’d like.

Thanks, I’m going to continue pursuing this option and try to get a proper quote for having it done.

@William83xj, I’ve enjoyed your thread on your conversion project. Are the new heads for that engine? I’m curious what led you to decide to use replacement heads. Yes, any photos would be appreciated. These are the 5.3L heads right?