i have read somewhere that on some aluminum head engines, have been overheated , that when shutoff hot, the valves material can be MICROWELDED to the seat!
so when cool and cam pushes valve open it can PULL the seat out with valve!
Damnifino?
ron

 

If there's room in the chamber ?, you will definitely have to go oversized seats, then the seat pockets will have to be machined for the new seats, the seats require an interference fit, I don't know the interference requirement for Jag heads, but would guess to be from .006" to .010".

The process for installing seats in aluminum heads consist of heating the heads to 300 or so degrees, freezing the new seats, then a guide is installed in the valve guide , and the seats are installed on a drift and hammered into place.

If, there is not enough room in the chambers for over sized seats, then the pockets for the seats will have to be welded up then machined, for the installation process.

You need to find a competent shop to do a proper install. If the heads have to be welded, make sure the welder is competent and does a pre-heat of the heads.

Don't cheap out on this, either do the seats right or just replace the heads, otherwise it will come back and bite you in the ***.

 

I share your reticence about posting on the internet, and I have no advice to offer. I wouldn't have replied to your post except that I have experienced the same engine damage as you, and it brought to mind my whole experience with Jaguar engine repair. I thought I would share it with you, for what it is worth.

First, some background. I have a '99 XJ8 and a'97 XK8. The former was purchased almost new many years ago and has been kept in excellent condition. Until recently, I have never had any problems with it. The latter was purchased sight-unseen on the opposite side of the country for a bargain price, and I definitely got what I paid for. However, It was been totally refurbished and is now in excellent condition.

Here is my story.

When I purchased the XK8, the engine failed almost immediately. That is where I started using my own judgment when I should have listened to my mechanic. I opted to have the engine rebuilt. My mechanic strongly advised against it and advised replacing the engine with a good, used one. My response was "Why would I do that? I would only be purchasing someone else's problems. With a rebuild, I would essentially have a new engine."

The rebuild was defective. The milling was faulty, and the engine was sucking coolant into the cylinders passed the head gasket. I was right back where I started. I could have insisted on having the work re-done, but for personal reasons decided not to do so. However, I got out of the situation at no cost. I then took my mechanic's advice and purchased a used engine with low mileage form a Jaguar dismantler with whom I have been dealing for many years. He stands behind what he sells. My mechanic replaced the timing chain. I think everyone knows that is essential on this vintage engine. Jaguar now sells an upgraded version. The timing chain, guides, etc. were replaced. The engine was installed. I have been driving the car regularly with only minor repairs ever since. I do not regret my purchase purchase. In fact, I love the car and get compliments on it even though it is 23 years old. But I do wish I had listened to my mechanic.

The XK8 is now my daily driver. As much as I love the XJ8, it has seen only infrequent use since I finished all the work on the XK8.

Fast forward. My XJ8 has never had any serious problems, and I have maintained it with scrupulous care. Nevertheless, things happen. About a year ago, I drove it into town and parked it in a shopping center parking lost. No problem. When I came out of the store and restarted it, it immediately ran extremely rough. I limped to my mechanic's shop. He put a scope into the cylinders and immediately saw exactly what you found upon dismantling your engine. A valve seat had lifted out of the head. I would not have thought something like that was even possible. Don't ask me how a valve seat lifts out while the car is sitting in a parking lot, and that is why your post caught my interest. Apparently, it happens.

I immediately contacted the same dismantler as before. Note, considering the age of the car, I did not think the prospects for finding a decent AJ26 (the AJ27 went into production after my car was build) would be good. To my surprise, the dismantler had an AJ26 with acceptable mileage, which he sold to me for $1,500 without any shipping costs. (He is fairly near my home.) For various reasons, I have postponed installing the engine. However, my mechanic has it at his shop. I will probably have it installed next month. My mechanic will, as before, replace the timing chain, guides, etc. and, then, swap the engines. Estimate is around $2,000 out the door.

I am a die hard do-it-yourselfer, but rebuilding a jaguar engine is something I could not possibly do. With my prior experience, I would not even have one rebuilt by a mechanic. It is very expensive and lots of things can go wrong. Fortunately, I got out of the rebuild at no cost. Needless to say, taking the car to a Jaguar dealer is out of the question. I don't even know anybody who can do that.

I have nothing but admiration for your courage in doing all this diagnosis and work your self. I wish I could. Best of luck in your project.

 

Like it or not, it is a relatively common problem on the 4.2 liter car. Same as some 5.0 liter cars have timing chain issues.This is what we have to put up with.

 

Thank you for your reply 🤗
Thank you for admiration , although unnecessary.
As o have said I have 35 years of engine building experience. 20 of them working on and rebuilding both ferrari and Lamborghini engines that I own.
An engine is still just a basic engine after all the electronics are taken away.
my son has his own engineering workshop so most of the milling/lathe work over the years are done by us.
New heads have been sourced and rebuilt and this weekend I will be re assembling the unit. The heads were measuring out of spec so I thought it's not worth taking the chance of any internal damage to the casting.
So if there is any specific section anyone would like me to post pictures of or give notes, please feel free.
Thank you again folks 🤗

 

Hi.
I bought a De Lorean with the same problem.
When it overheated the aluminium head expanded more than the valve seat and it dropped. Get an expert shop to repair the head or it will happen again.

 

Did you actually read my last post?

 

Everyone!
PLEASE stop reposting the OP's first set of pictures!!!!!!
You can easily delete them from the "Quote" section!!!!

 

Can any one help me in identifying the part number for this hose please🤔
Its the one that runs directly from the thermostat housing its self. I have looked but cant seem to find it🤔

 

There is a connecting tube linking it to another hose correct? I think you can only buy it as a set (2 hoses and the connecting tube. C2P2126

 

Thank you🤗
just looked up that code, it comes back as for a supercharged engine. Does both the NA engine and supercharged engine share the same coolant pipe layout?

 

sorry I blanked and was thinking SC.
Lower radiator hose to VIN B02896 - C2P2159. From VIN B02897 - C2P11448

 

This reminds me of when I used to work at a Toyota dealership. For the longest time Toyota had a problem with their V-6 cylinder head gasket because the block was cast iron and the heads were aluminum. From heating expansion and cooling shrinkage at different rates it would eventually tear the head gasket. Toyota went though over 9 revisions of this gasket and eventually from certain years (up until 1995 I think), they gave a lifetime warranty on this repair and if it ruined the block they would also replace that for free. However this was not publicly advertised and those that wasn't aware of this will have their own mechanic fix it not realizing taking it to the dealership would have costed them nothing.
I hope there is an updated material that would prevent you from doing this in another 70k miles!
Thank you for the very detailed repair as you go pictures!

Alan.

 

don't know what the problem is, but you have my sympathy

 

Buy a $30 OBD temp gauge and just stick it somewhere you can see it.

On the 4.0 it moves off the middle at 115C which isn’t really all that toasty, I’ve heard on the 4.2 it stays in the middle till 126 which is a bigger problem. Some aluminum motors are just tanks when it comes to overheating (BMW M62) and others just aren’t as forgiving.

 

GAAAAHHHHH!!!!!!!!!!!!!
The OP already knows what his own pictures look like, you do not need to show them to him again. They are REposted I think six times now. We've all seen them too many times.

 

hahahahahha

Let’s make it 7 !!!!!! 😁😁😁

 

LOL....Six posts after you said "don't do it". he does it. I wonder if he's taking the p**s?

 

Thankfully, no i dont =]

 

SBS, I know you only used the green stuff for temporary solution. But Phobman, I don't think that's right, checked with my car savvy CA friend, he wrote back: "We have green for old-fashioned cooling systems, and yellow/orange for aluminum motors and radiators. "

So X150 owners, do not use the green stuff unless a stop gap situation.