Series 3 4.2L engine slotted block

I have a 1985 XJ6 Series 3 in Thailand which is UK spec and RHD.

I have been having trouble with head gasket coolant seepage. I fitted new valves & springs about 18 months ago and the car was running well apart from there was a gradual loss of coolant. It took me a long time to find out where the coolant was going, but eventually I discovered that there was a seep of coolant from the head gasket into cylinder #01 (although all cylinders still had good compression). I could see drips of coolant forming at the top of the cylinder by using an endoscope down the spark plug hole.

I removed the cylinder head and sent it to the machine shop for a light skim and re-fitted it with a new head gasket last week. All the head studs were replaced last year when I did the valve work and they are all in the correct places for the various lengths due to engine lifting eyes etc. I have checked that there is plenty of thread for the dome nuts to clamp to the correct torque. Before fitting the head I checked the top of the block for trueness with a straight edge and feeler gauge; it appears to be true to better than 0.004".

However, I now have coolant seepage into cylinder #03.

My engine block is the 8L slotted block version without liners. The slots in the top of the block appear to be filled with brass or similar and end in circular pieces with holes in the centre which are about 1/8" diameter. I cleaned out those holes of debris - they appeared to all bottom out at about an inch depth.

Should these holes be bottomless? I am wondering if this is part of my problem as coolant is trying to flow through them but is unable to, hence leading to some additional pressurised coolant at the cylinder head and block mating face. Unfortunately I didn’t tke any photos of the slots.

I also think the head gasket is odd in that the holes for the studs (approximately triangular in shape) have no seal ring around them, despite the fact the studs are “wet”. All the other coolant passages have an orange seal ring around them. I have read elsewhere here on the forum that some people have added a ring of instant gasket around the studs where they come through the top of the block. Also some recommend using copper size on both sides of the gasket, neither of which I did last time or the time before. Perhaps a combination of these three issues is leading to my problem with coolant seepage.

Any comments, suggestions, ideas etc would be gratefully received.


Are you fitting the gasket right way up?

IIRC tHe metal fire rings seal best with the smooth side over the slots, not the folded edge side down. Never seen brazed slots but never had a late 3.4…

Yes gasket was fitted as you describe each time with the metal areas over the slots.

Engine is 4.2 (8L prefix number)

Picture of a gasket to show what I mean about the orange seal rings around water passages, which are not present around the stud holes

Too much thread, perhaps? Are you 100% the nuts are clamping and not bottoming-out?

This can happen if the studs are not fully home. Or if the wrong nuts and/or washers are used.

Ask me how I know :slight_smile:


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When I fitted the head last time, I just nipped up all the dome nuts, then removed each one in turn and took away the washer. I then verified each nut could screw all the way down to the face of the head without bottoming out.

The back right one was a bit tight so I added a washer. That is one of the 4 short studs.

Then replaced all the washers and torqued down in sequence.

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You seem to have recognized all pitfalls, Andy - and done all the right things…

The last defense against water leaking into the cylinders are of course the metal seals - for what it is worth. Questions arising; when you checked the block (and head?) for straightness - did you also check for minor imperfections? And first time around; was the signs of water seepage on the surfaces? In my book the water passages should be triangular - the stud holes circular? In all cases; the gasket should be installed plain - no added sealants should be required, and is usually counterproductive…

I don’t know the precision of your torque meter, though it is not really supercritical - but did you torque up in one, two or three steps? You could do a retorque; backing of each stud half a turn in the torque sequence - then retorque to correct value in in one sweep. It’s of course very important that all torquing is done in a continuous sweep to the value desired - not ‘inching’ it up to the set value. The sweep should show a steady increase in readings - sudden increase or unchanging readings is a danger sign…

Not much help - but are you sure the seepage is real and not spurious…?

xj6 85 Sov Europe (UK/NZ)

The seepge is real - here is a picture from the endoscope showing a drop of coolant forming at the top of the cylinder:

When I removed the head (about 2 weeks ago), the face of the head had a suspicious area on #01 where I think coolant seeped from a coolant passage to the cylinder. It is bottom left in the picture that follows:

As you can see, that coolant passage was enlarged due to corrosion in the head, as were most of the others on the exhaust side. I had the machine shop repair the passages back to standard size then skim the head. I was hoping that was the reason for the problem. You can also see in that photo the triangular shape of the area where coolant has been in contact with the head around the stud due to the shape of the gasket.

I have been searching this forum and others, and have now found some photos of slotted blocks. All the pictures I have found show the slots completely open and open holes at each end. On my block, the slots have been filled with something and the circular holes at each end have what looks like a ferrule inserted, reducing the bore of the coolant passage to about an eighth of an inch. These holes seem to bottom out about an inch down. I didn’t photograph this but the picture below is cropped from a larger photo and shows one of the slots before the block was cleaned up.

Looks like perhaps I should focus on these when I get the head back off again. I am currently away from home at work for a few weeks so won’t be able to carry on working on this for a while, but am trying to gather as much advice and information as possible before I start again.

That MUST be repaired, and head flattened, or no gasket is likely to work.

Yes - as mentioned in my previous post, I have had the corrosion repaired by the machine shop and the head skimmed.

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Have you checked the deck with a machinist’s bar?

No. I don’t have one

If you have access to a machine shop, one can be made fairly easily: before putting the head back on, It would be critical to determine flatness, otherwise your effort may be wasted.

I have used a carpenter’s framing square. A large one.

seems to me that a PO had fasket issues and blamed the slot. filled it in and intoduced small holes / Reduxe the fuynction but keep aome and seal better.

I despise stop leak. but, machinists of old have resorted toa subsyance that crystalizeds in small passagel leaky studs in ol fords “fixed” in that manner;


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I have checked them against a machinist’s bar: good, but can vary in flatness up to .002".

One would be a decent indicator, but insufficient if one wanted to use a tin gasket. I think the use of a Payen or standard Cometic gasket would be warranted.

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To me that implies a wrong, or wrongly fitted, gasket, Andy…

Paul is on to something; while the picture of the repaired block sections seems ok - is the block truly flat? And when getting the new(!) head gasket; a more minute examination of the respective matings, head to gasket, gasket to block - ideally that the head and block passages mates up perfectly, which is difficult to compare directly. The repairs may not be accurate?

The reason for the confirmed(!) seepage is still unexplained - but with perfect mating, block-gasket-head, there should be no leaks!

xj6 85 Sov Europe (UK/NZ)

In the absence of a straight edge and uncertainty regarding the flatness of components how about removing all the studs from the block and use engineers blue to determine where things touch?

Here is a photo of the top of the block with the gasket still in place just after the head was removed. As the long studs are “wet”, you can see why there is a triangular shaped mark left on the mating face of the head as seen in the picture in the earlier post. The larger coolant holes are on the exhaust side, so the gasket is the correct way up.

I bought the gasket from SNGB P/N EAC2957 which is the correct part number for the Series 3 4.2L engine.

I think the gasket design is a bit odd as all the other coolant flow holes have the orange seal ring around, yet the stud holes do not. I have read in other posts on this forum that some people put a bead of sealant around the studs where they come through the top of the deck. I will do that next time.

When this gasket ws fitted, I did not have the head skimmed. False economy as it does show some signs of starting to fail between 6&5 and 5&4 combustion chambers.

I will take the various pieces of advice so far when I get back to working on this. I plan to remove all the studs again and clean the deck of the block using a steel block and abrasive paper until it is spotlessly clean. I have been convinced that I did not clean the block face thoroughly enough last time before re-fitting the head. Also investigate further what the filling is in the slots and check there is still flow across from inlet to exhaust side, and through the holes from head to block. Perhaps remove those ferrules as they must be restricting flow and so perhaps causing a problem.

Not having worked on these engines before, I previously thought the brass insert (or whatever it is) was standard.

I will obtain a new stright edge and check the trueness of the block face again once thoroughly cleaned up. I am tempted to use copper size on the gasket as well, having read on another thread on this forum that it is highly recommended by some engine builders.

Any recommendations on where to purchase a Cometic gasket?

Copper dressing is for steel embossed head and manifold gaskets, where fitted. On S3 engines, that isn’t an issue.

I presume the renovation of the coolant passages involved building up the area with welding, then reboring the oval holes and remachining the surface flat? If so, perhaps your weeps come from porous welds. I don’t even know how you’d make sure welds weren’t porous, other than having a very skilled welder do the work.

When setting the studs, Andy, make sure they protrude the same distance above the head - it is an indication that they are fully seated in the block. Your original test of stud protrusion versus acorn nut depth was well conceived, but calipers may be better - also bearing in mind the slight compression of the gasket with torque. But mating surfaces must be scrupulously clean - and imperfect cleaning may be a likely cause, as may indeed be a ‘warped’ block surface…

And Kirbert is right, alu welding is tricky…

You really deserve a better outcome than that leak…

xj6 85 Sov Europe (UK/NZ)