I guess the main reason would have been commonality of parts; same crank forging? Same or similar block moulds? Maybe not worth (re) tooling for the original 3.4, given the relatively small numbers involved.
Sure, likely the same crank (stroke and bearing apacing and -size), and maybe also the same machineryā¦ if it has the same stroke did they just make the bores smaller and the block is the same?
And yes, no way they could have paid for new or different tooling for an aging engine design in the less demanded displacement. So only change the bore and put in new pistons, can that be all?
Yes, both engines use the 106mm stroke, but different part numbers, presumably they have different balance factors.
1 Like
**
To amplify, David; I think they used the same block, and stroke(?) from the āoriginalā 3,8, and altered the bores for the 3,4 and 4,2 - and the latterās bore is about 0.4" or 9 mm bigger. Which leaves very little metal between cylinders.
The 2,8 uses a different block - with the same bore as the 3,4 but with shorter strokeā¦
Frank
xj6 85 Sov Europe (UK/NZ)
**
The slot shown doesnāt really seem factory made, Andy - it seems offsetā¦?
I wonder if the PO, or āsomeoneā added the 'brass filling" you removed to give a better gasket sealing - as indeed Carl implies? And this āoldā set-up didnāt have any leak problemsā¦?
And the gasket not fitting is an oddity - did you actually compare the original gasket with the replacement - which may have cast some light on the issue. And certainly compare either with the Cometic one when you get it - a āwrongā gasket leaking would explain a lotā¦
Frank
xj6 85 Sov Europe (UK/NZ)
As I understand it, the original 4.2 block required respaced bore centres to allow for the larger bore, so the crankpins are relocated compared to the original 3.4, 3.8 engines. The later 3.4 engine, as fitted to the XJ, is based on the respaced 4.2 engine with assymetric bore spacing, so has no real affinity to the original 3.4 which, of course, dates back to the beginning of time. All XKs apart from the 2.4\2.8 use the 106mm stroke , both of them using the original 83mm bore with different strokes. I think the 2.4 \2,8 engines are related to the original dimensions, whereas the 4.2 and later 3.4 had different spacings which meant they lost the original balance and smoothness of the originals. Others may know more.
2 Likes
Itās factory alright
The cheaper gaskets rarely fit well, add to that a slot that wasnāt machined well and it canāt ever seal well.
Would a steel gasket solve the issue?
The slots are definitely factory done but as you say are not aligned evenly between bores. Of course, the problem area I have identified is one of the smallest lands between a bore and a slot, and compounded by the poor alignment of the gasket at this point. I cannot imagine anybody would dream up the idea of adding slots to a non-slotted block, nor enlarging any slots. I have found a photograph of somebody elseās slotted block on the internet and the slots follow the same pattern as mine.
I think this is the right conclusion: a previous mechanic decided to fill in the slots in a bid to stop coolant leakage. However it did not work as the car has lost coolant since I have had it. The infills were not well done as they had not been machined flat after fitting, so there were rises and falls in the suface where the head meets. Hence I decided it best to remove them all and return to standard. Also the smaller coolant passageways were plugged so the coolant flow would have been less than designed. Another thought is that cast iron and brass expand and contract at different rates so I donāt think it is a good idea to use brass to try to fill the slots anyway.
I did not compare the gaskets I have been using with the original one I removed. That came off about 18 months ago when I worked on the valves and at the time I saw no need to retain it. (I was not chasing the coolant loss problem at that stage).
I have queried with the suppliers of the gasket if they could be faulty or different from original equipment in layout. (I have actually used 4 head gaskets now trobleshooting this problem.) One supplier has sent me a Payen gasket FOC as a replacement. I have not been able to inspect it yet as I am away from home. The other supplier says they compared the aftermarket gaskets they sell with the Payen version and that they have identical layout. Hence why I have ordered the Cometic one.
On my last-but-one attempt to cure this problem I used copper spray. I was not impressed with it. It did not seem to stick properly and I will not use that again.
I have added Liqui-Moly Stop Leak. But is doesnāt, at least not in this case. I cannot source any other brands of similar products in Thailand. The one with the best reputation is K-Seal, so I plan on getting some of that from overseas for the next attempt.
The gaskets I have been using are MLS.
The one Cometic are making for me is apparently fibre. I have read that fibre gaskets are more āforgivingā so maybe it will give me a better chance. I hope so as it is very expensive at Ā£160 including VAT and carriage. compared to Ā£10 for a pattern part MLS one and Ā£50 for a Payen MLS one.
**
Have you compared those, Andy - if they are ādifferentā it at least adds to our knowledgeā¦
**
Payen has a good reputation - copies, even faithful ones, may of course be equal, but letās hope the Cometic solves the problem. But the problem may be unsolvable, though how the block passed Jaguar quality control and later customer guarantees is a mystery.
Any coolant additives to stop leaks is basically counterproductive; they usually wind up clogging passages they should not - it is not the proper way to stop leaks. In this case, with coolant entering the cylinder; it means that additives is subject to high pressure and temperatures - and basically they are meant to ācureā in contact with ambient air, ie external leaks. I suggest you desist - it will not work, and additive will find its way into the engine!
**
Must certainly have metal inserts round the cylindersā¦?
Frank
xj6 85 Sov Europe (UK/NZ)
The four head gaskets (pattern parts, unbranded) all had the same layout as one another, and I think must be from the same manufacturer, even though supplied by two different parts suppliers.
The official Jaguar workshop manual instructs to add Barrs Leaks to the coolant after changing the head gasket, so it seems to have been standard practice with these engines from new! Opinons on āstop leakā products are varied and diametrically opposed, that is to say some swear by it and others avoid at all costs. The same seems to be true of copper size on head gaskets.
The info I can find on the Cometic fibre gasket reads:
āThis Cometic CFM gasket is a perforated-galvanized steel core with an asbestos-free fiber material that is applied to both sides. A stainless steel core with reinforced fiber facing is ideal for head gaskets, allowing heat to be drawn evenly across the gasket surface while providing maximum sealing characteristics when exposed to coolants and oils.ā
On some suppliersā websites it is listed in the āCompetition Head Gasketsā section. I have ordered direct from Cometic UK.
Did you say you were in Thailand ?
Are labor rates low there ?
What about a handmade annealed copper head gasket ?
I see those Pakistani guys on Youtube fix all manner of automotive problems in very clever ways.
A copper head gasket is an accepted technology
Have you considered the possibility that the block could be cracked at that spot? The crack could do small that it invisible to the naked eye when the black is cold, but will let coolant through when hit and the cooling circuit is pressurized.
Yes I live in Thailand. I have not found any fabrication shops that make gaskets yet. There is a well-established car manufacturing industry here and they export a lot of vehicles. Hence I think the mainstream cars are well supported with parts supply. Classic cars are rare here.
I cannot see any evidence of a crack, and neither did the machine shop when they skimmed the block face. another factor that makes me think it unlikely to be a crack in the block or head is that the leak moved from cylinder 1 to 3 then 5 at different stages. A crack would always have the problem in the same place.
My theory at present is that the land between the bores and slots is so minimal that the gasket has to be spot on perfect to seal properly, and these pattern gasekts just are not accurate enough.
Still open to more suggestions though!
I donāt want to belabor the point butā¦
I had two (S2) engine blocks that look perfectly fine, visual inspection by the shop, no problem.
I paid for magnaflux tests, both blocks turned out to be cracked between the cylinders, one of them EVERY wall! The cracks became visible only after applying the dye.
And Iād hate to bear bad news, but a block could have more than one crack and the effects of these cracks be intermittentā¦
You can now buy DIY magna flux kits.
**
Were all 4,2 āslottedā Kevin, or was that added later based on bad experience, cracking, at a later stage as was staggering boresā¦?
That headgaskets do not fit perfectly sort of implies something mixed upā¦?
Frank
xj6 85 Sov Europe (UK/NZ)
No, not all 4.2 blocks were slotted. Earlier blocks, both short and long stud, do crack between bores (which is not a real issue if itās just the small cracks, and because of the liners the cylinders themselves remain intact).
The head gaskets fit universally, later gaskets have a few extra holes. Earlier block, later gasket:
Hi Frank,
The staggered bores were required from day 1 to allow for the larger bore of the 4.2; noās 1 and 6 were moved toward the ends of the block, 3 and 4 towards the centre and 2 and 5 remained where they were. According to my book ( Thorley Original XJ) the slotted block was introduced at the end of '79 ( Series 3) and required a modified head to match with the slots. However, Thorley also states that the Series 1 used the same engine as the 420, which, as far as I know, is incorrect, as that car used the short stud engine as used in the contemporary E Type, whereas the 7L block in the XJ uses the long stud block, shared with the 420G. According to my parts book, block, head AND gasket changed from engine no 8L89109, ( S3 engines) so presumably that is when the change took place. The 3.4 block and gasket did not change, but the head did, at engine 8A15506; there was a further head change at 8L167199 for the 4.2, but no description of what the change entailed, but as the gasket stayed the same, presumably it wasnāt around the area we are discussing. Illustrations in the SPC do not show the slots in either block or gasket
1 Like
Giving this some thought. The 3.4 as used in the XJ was introduced in the Series 2, so in that guise, would not have had the slotted block that was introduced early, but not immediately in S3 production. Nothing in the SPC suggests that the 3.4, unlike the 4.2 was modified with the slotted block. Furthermore, IIRC, the 3.4 didnāt have the big valve head of the S3 4.2, so probably still had the old S2 head , which would not have been slotted. So, does the OPās head have slots that line up with the block, and if so, is it possible it has been fitted with a big valve S3 head? And, again, if so, are the combustion chambers larger than the 3.4 head and so not clamping the gasket around the cylinder ring? Part no for 3.4 gasket according to my factory parts book is C41016; are we using the correct gasket? Just a thought.
**
Referring to Davidās clear picture, Kevin - the bores are equidistant, ie, the the distances between the cylinders are same. Which means the āend to endā cylinders were longer than in the original set-upā¦?
In which case, it would explain that Andyās gasket not fitting as it should somehow implies that his gasket somehow is meant for something else? He says that moving the gasket one way it wonāt fit at the other end - like the gasket was somehow made for an āunstaggeredā engine?? Looking again at Davidās picture, bless him, his gasket fits like the proverbial glove.
I wonder if Andyās engine block is what it is supposed to be, or of course that the gasket manufacturers have botched the job - without ātheā proper gasket his leak problem is certainly unlikely to be solved. His engine number may elucidateā¦?
Frank
xj6 85 Sov Europe (UK/NZ)