TD 2.5 XJ welch plug mystery???

[Off track]

Hi All.
I have just pulled the heads of the old girl because the 4 welch plugs near the exhaust manifold are leaking. (there was silicone in the holes not sure if VM has developed form-a-welch-plug 20 years ago) My question is after removing the silicone and bolts the lower plugs near the block are corroded and there is a rust spot inside the top small hole. behind the intake gasket that leads to the same head bolt as the lower welch plug hole. is there a small plug at the top too, less than 10mm?
none of my diagrams shows it but there is something in there corroding away. ill see if I can add a photo.

[layback40]

Welcome to AJOR!
The 2 holes that go into the head bolt do not have plugs. It sounds like someone in the past has done a bad job. VM did not use silicone. I have probably had heads of these engines more times than I care to admit. Wen assembling, the head bolt holes need to be clean and the bolts and holes need a coating of anti sieze. All bolts and nuts should get a coating. The best gasket sealer is Hylomar. I have reused head gaskets by cleaning them, removing all the black paint, seperating the laminates and coating around the liners and other holes with a thin coating of Hylomar. It seals heads very well. 100,000km and no problems here. The heads need to be hardness tested. Simply try and scratch the surface with a screwdriver blade in a place that is not important. If its too hard to scratch it, the head has not been cooked. If it scratches it, you will probably need to replace the head. Make sure you never use straight water in the cooling system. I use a good quality inhibitor at 2X normal concentration and distilled water. Coolant is fine also.
You can use silicone on the rocker cover gasket.
While you have it in pieces you should replace the Orings on the oil cooler.
Good Luck!

[Off track]

Hi Layback.
I was hoping you would see this as I've read many of your posts on the 2.5 diesel, so knew you had quite some experience with them.
Not meaning to be argumentative, but there are definitely welch plugs in the inner side of the bottom holes, past where the bolt sits, these have corroded and can be seen through from the water jacket holes and through the holes past where the bolts (M2)sit. (see photo)
This is shown in parts manuals as VM part 4723 210. In the upper small hole, the manuals showed nothing inside past the bolt. but I defiantly have a rusty plug/grub screw/dowel or something that I cant see the back of through the water jacket and I've not seen welch plugs that small before.
I was really hoping someone has dealt with(rusted small hole plug) before and could point me in the right direction so I don't end up pushing it through to where It can't be retrieved.
The one in the photo looks more like a grub screw than the others.
Yes the silicone was on the outside of the bolts and doing nothing.

The heads were able to be scratched with the corner of a new flat screwdriver, only scratched, just feelable with a fingernail. certainly will not dig into the Aluminium or make swarf. small enough that a gasket would still seal over the scratch.

.

[Off track]

The scratch test more just removed the carbon than a scratch.

found a 2000 XJ head parts diagram. showing 2x plugs
listed as 4, and 17.

does anyone know if these are the same as mine?
Mine is a 97 XJ VM 425. 1 head gasket not individual head gaskets.

has anyone had to replace these? in particular the smaller top ones?

[layback40]

Originally Posted by Off track

The scratch test more just removed the carbon than a scratch.

found a 2000 XJ head parts diagram. showing 2x plugs
listed as 4, and 17.

does anyone know if these are the same as mine?
Mine is a 97 XJ VM 425. 1 head gasket not individual head gaskets.

has anyone had to replace these? in particular the smaller top ones?

I thought u were saying there was a plug between the bolt hole and the outside akayour silicone plug. There are plugs deep inside behind the bolt hole.Out of the 16 heads I have here, none have corroded plugs.
I think your engine may have had bore water or dam water as coolant at some stage.
All my VM425's are single gasket type. The heads are the same for single or multi gasket applications. The difference being the plate that equalizes the end bolts must be longer by the thickness of the gasket in the multi gasket applications.
My comments about gasket reuse are for the single gasket type and I have done it on both my VM425's.
If you measure your bolts and they are in spec, they can be reused.
My scratch test needs to be done on a clean head surface. Maybe practice on the inside of the rocker cover first. It will give you an indication of the force to scratch soft alloy. The head surface after cleaning should be a slight bronze colour. If not it has probably been machined or overheated too many times. There is no allowance for head planeing. The heads can not be retempered once they have gone soft. They are prone to cracks/leaks around the injector holes and under the valve seats.
The main difference between yours and the very late ones is that yours probably has one temperature sensor, the later ones have 2. The engine control computer located behind the heater, on the early ones has about 60 pins in the plug holes and the later ones have around 90. The early ones have a MAF in the outlet of the air cleaner, later ones just have a MAP in the inlet manifold.
There were many of these engines used in other applications in the UK and EU. The VM facebook group has some very knowledgeable members, I am not on par with them but I am a member.
Most parts are best obtained out of the EU or UK.
Be careful about purchases on ebay as there was a 4 cylinder petrol XJ and many sellers get them mixed up with the VM diesel.
If you want it to have much more go but shorten its life, I have a spyder tune box here that I have never used. You will need an inline fuel pump though as the fuel supply system struggles at times to keep up.
Dieselwiesel who posts some times is a very smart guy when it comes to getting more power out of the 425. You can trust what he has posted.
Mudmonster is another who used to post on here who knows his stuff.

[Off track]

more photo's.
I bought this car 3 months ago has 138K on the clock. old owner drove it with a trailer to the dump 3 times a year since 2004. It has sat idol a lot and never had a good run in 17 years 26k added to the odometer in the last 17 years according to rego papers.

I changed the oil and coolant new brake callipers and cylinders/ masters and slave for the clutch as these were weeping from lack of use. So looking for issues from sitting.

It was not getting hot when driving it but was slowly losing coolant, I had lifted the overflow tank (as per dieselwhesel post) so had good notice when low.

From tests I think the heads are good apart from the welch plugs in the heads.
I read that the welch plugs can be an issue for others but if not the head ones which ones usually give trouble? would like to get them while its stripped down.

Also there is a lot of oil at the rear of the engine, much of this is from the breather hose being split. Has anyone fitted a catch can instead o the filter from the factory that looks to drain back to the sump?

[layback40]

I am surprised the clutch slave was leaking as its plastic.
My guess is it sat with water, not coolant in it. probably the high humidity has been hard on it as well.
Surprised that you got the exhaust manifold off the turbo while in place. That back flange nut is untouchable. Normally when taking the heads off you leave the exhaust manifold attached to the turbo and undo the exhaust mounts so you can get it out of the way.
I have no experience with changing welsh plugs as I have never needed to. They should be an off the shelf item. Dont use brass ones though as they would cause increased head corrosion.
As mentioned before, Hylomar is the sealant you need to be using.
Given the low kms, once you sort out the issues, it should be a good jeep for a long time.