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At best the Four.Two litre Jaguar/Daimler engine block could be described as suspect and its quality further declined via its production. It was designed in the early 1960s to give more torque and better low to mid range spectacle than the Three.8 litre engine, which it genuinely did. Early examples (fitted to the last Mark Xs, the E-types and the 420s until about 1968) are lightly distinguishable from the XJ6 blocks by two fewer waterways at the rear (see your cylinder goes), three large core buttplugs per side and studs screwed directly into the block face. The later engines are usually prefixed 7L (all Four.Two litre engined Jaguars from one thousand nine hundred sixty eight to 1975) or 8L (1975 onwards) and these are the ones covered in this article.
The pre-XJ6 block was said to be improved upon by the 7L block, which had a more efficient internal cooling flow. The problem was that the cylinder head studs screwed directly into the base of the block, through the waterways and, if the correct coolant is not used, then they will rot out very quickly. These studs are also twice as long as the pre-1968 blocks, permitting more open up and therefore more variation in clipping pressure against what has been set with the torque wrench and this makes it more prone to head gasket problems. This improved block cracks, usually hairline cracks appearing in the block, eventually becoming stepped (when one side becomes slightly higher than the other) and the liners drop. The 8L block, a strengthened 7L block, cracks even more than the 7L, and this may be due to an increase in thermostat temperature or to unweathered blocks being used or, possibly, a reduction in standards under British Leyland.
Why do they crack?
They crack because of the very high temperature differentials created by inefficient coolant circulation. Coolant can circulate around the block only at the very front and the very back. The water pump outlet is placed so that when the thermostat very first opens, super cooled fluid is pumped mainly down the harass side of the block. The inlet side with its much less efficient circulation, remains closer to the thermostat temperature. This means that you could possibly have zero degrees C fluid injecting the harass side of the block and eighty eight degrees C fluid (fuel injected cars) leaving the inlet side. The cooling fluid then passes up through the cylinder head mainly from the harass side, passing out through the inlet manifold, again maintaining the temperature differential on the inlet side of the block. This problem – actually solved in one thousand nine hundred eighty one by machining latitudinal cracks (slots) across the block and so fluid was able to circulate from the harass to the inlet side inbetween the liners, equalising the temperature in this powerless area. Unluckily this gives you only about one hundred eighteen inch for the gasket to seal on inbetween the waterways and the combustion chamber, which is riot much thicker than a core butt-plug. So, if the correct coolant fluid is not used it corrodes through at this point and the block is scrap. Also if the head gasket goes (which it does frequently) and it is left too long, it bums through at this point and the black is again scrap. This is now causing more problems than the original cracks.
What can be done to recover the block?
Many Jaguar specialists say these cracks don’t matter. Some remarkably big names do nothing about them and all they do is skim the block face. I quote: “What can we do, we cannot throw the majority of Four.Two litre engines away and we get very few comebacks under the twelve months warranty”. Certainly, by skimming the block (to liquidate irregularities such as stepping) flushing and fresh studs, most engines will last, at least the twelve months before the head gasket goes. But there are methods which used to deal with the problem more effectively:
– Cold Stitching
This is where you drill crevices each side of the crack, thread the fuckholes and screw in brass rods, then skim. The idea is that the rod expands mere than the block metal when hot and so closes the crack.
– Welding
You pack directly into the crack and then pack the resulting crevice with weld, then skim. This may work by creating a wedge of fresh metal over the crack (which incidentally extends over one inch downwards). However, talk to a metallurgist about welding large cast metal areas without pre-heating!
– Ceramic Covering
This is where the inwards of the block is glazed with resin which glues the cracks together. But there is only one method which is foolproof as it not only works but it improves on the original block and solves the problem indefinitely.
– Top Hat Liners
This is where the old liner is machined out and a recess is machined in the top of the block. A fresh liner is then pressed in. This has a lip around the top edge which fits into the recess. The tops of the liners touch each other so the head gasket now seals on the top of the liner and not the block. The extra advantages of this we that you can come back to a standard bore (standard pistons tend to be cheaper) or the original pistons (if in good condition) can be reused. It also means that if required for a spectacle rebuild, the block can be bored out to Four.Five litres.
The procedure when preparing the block is as goes after: 1. The block should be ideal without cracks and corrosion (slotted blocks) Two. The fact that the block is not cracked at the point you rebuild it does not mean it has not embarked to crack. Three. If there is any bowing then the block will require the crank carrier to be line bored. Four. Send for boring and honing. Five. Liquidate all core buttplugs and the rear engine plate. Then spend twenty minutes with a pressure washer to eliminate sediment and rust from inwards the block. Chemical cleaning can stain bearing faces, bores, etc. 6. Eliminate all the oil gallery buttplugs (not leaving behind the petite conical gauze fitter behind the hydraulic chain tensioner), then pressure wash, preferably with detergent, all the oilways. 7. Substitute all the long studs, 8. While being substituted, the studs will rum sixteen to seventeen turns into the block, permitting for the domed cylinder head nut to tighten onto the head and not torque up a few threads above the spacer. Four studs are slightly longer than the others; this is for the engine lifting brackets.
The main contributing factor causing blocks to crack is due to the thermostat. When a car boils up you are told to let the engine coal down before topping up with coolant and that this stops the thermal shock which causes cracking. An eighty eight degrees C thermostat permits the engine to reach twelve degrees C less than boiling point before opening broad to permit the block to be swamped from one end by super cooled fluid from the radiator. In other words, your engine receives a thermal shock every time the thermostat opens.
To reduce this you can eliminate the puny back flow tag and drill another slot the same size in the thermostat, permitting fluid to pass through the system and so help equalise the temperature of arguing and outgoing fluid. The engine will take three to four minutes longer to reach operating temperature but it helps stop the head gasket gargling.
Do not leave the thermostat out totally since the fluid will only circulate around the front of the engine mid this causes hot catches sight of. Make sure you use the correct thermostat on early pre-XJ6 engines as many of the early Trio.8 litre ones with cracks have been fitted with the smaller modem thermostat. Carburetted cars run well with seventy five degrees C thermostats drilled as above; fuel injected cars need an eighty eight degree C thermostat drilled to cancel out the warmth.
Cracks in the block may not always be apparent unless you have good eyesight and are specifically looking for them, so use crack test fluid. A non-Jaguar specialist would not necessarily notice them because they may not know to look for them.
Fighting the Flaw in the four
Jaguar Car Club of Tasmania
What’s Fresh
Join Us
At best the Four.Two litre Jaguar/Daimler engine block could be described as suspect and its quality further declined via its production. It was designed in the early 1960s to give more torque and better low to mid range spectacle than the Three.8 litre engine, which it genuinely did. Early examples (fitted to the last Mark Xs, the E-types and the 420s until about 1968) are lightly distinguishable from the XJ6 blocks by two fewer waterways at the rear (observe your cylinder goes), three large core ass-plugs per side and studs screwed directly into the block face. The later engines are usually prefixed 7L (all Four.Two litre engined Jaguars from one thousand nine hundred sixty eight to 1975) or 8L (1975 onwards) and these are the ones covered in this article.
The pre-XJ6 block was said to be improved upon by the 7L block, which had a more efficient internal cooling flow. The problem was that the cylinder head studs screwed directly into the base of the block, through the waterways and, if the correct coolant is not used, then they will rot out very quickly. These studs are also twice as long as the pre-1968 blocks, permitting more spread and therefore more variation in clipping pressure against what has been set with the torque wrench and this makes it more prone to head gasket problems. This improved block cracks, usually hairline cracks appearing in the block, eventually becoming stepped (when one side becomes slightly higher than the other) and the liners drop. The 8L block, a strengthened 7L block, cracks even more than the 7L, and this may be due to an increase in thermostat temperature or to unweathered blocks being used or, possibly, a reduction in standards under British Leyland.
Why do they crack?
They crack because of the very high temperature differentials created by inefficient coolant circulation. Coolant can circulate around the block only at the very front and the very back. The water pump outlet is placed so that when the thermostat very first opens, super cooled fluid is pumped mainly down the harass side of the block. The inlet side with its much less efficient circulation, remains closer to the thermostat temperature. This means that you could possibly have zero degrees C fluid coming in the harass side of the block and eighty eight degrees C fluid (fuel injected cars) leaving the inlet side. The cooling fluid then passes up through the cylinder head mainly from the harass side, passing out through the inlet manifold, again maintaining the temperature differential on the inlet side of the block. This problem – actually solved in one thousand nine hundred eighty one by machining latitudinal cracks (slots) across the block and so fluid was able to circulate from the harass to the inlet side inbetween the liners, equalising the temperature in this feeble area. Unluckily this gives you only about one hundred eighteen inch for the gasket to seal on inbetween the waterways and the combustion chamber, which is riot much thicker than a core buttplug. So, if the correct coolant fluid is not used it corrodes through at this point and the block is scrap. Also if the head gasket goes (which it does frequently) and it is left too long, it bums through at this point and the black is again scrap. This is now causing more problems than the original cracks.
What can be done to recover the block?
Many Jaguar specialists say these cracks don’t matter. Some remarkably big names do nothing about them and all they do is skim the block face. I quote: “What can we do, we cannot throw the majority of Four.Two litre engines away and we get very few comebacks under the twelve months warranty”. Certainly, by skimming the block (to eliminate irregularities such as stepping) flushing and fresh studs, most engines will last, at least the twelve months before the head gasket goes. But there are methods which used to deal with the problem more effectively:
– Cold Stitching
This is where you drill crevices each side of the crack, thread the crevices and screw in brass rods, then skim. The idea is that the rod expands mere than the block metal when hot and so closes the crack.
– Welding
You pack directly into the crack and then pack the resulting crevice with weld, then skim. This may work by creating a wedge of fresh metal over the crack (which incidentally extends over one inch downwards). However, talk to a metallurgist about welding large cast metal areas without pre-heating!
– Ceramic Glazing
This is where the inwards of the block is covered with resin which glues the cracks together. But there is only one method which is foolproof as it not only works but it improves on the original block and solves the problem indefinitely.
– Top Hat Liners
This is where the old liner is machined out and a recess is machined in the top of the block. A fresh liner is then pressed in. This has a lip around the top edge which fits into the recess. The tops of the liners touch each other so the head gasket now seals on the top of the liner and not the block. The extra advantages of this we that you can come back to a standard bore (standard pistons tend to be cheaper) or the original pistons (if in good condition) can be reused. It also means that if required for a spectacle rebuild, the block can be bored out to Four.Five litres.
The procedure when preparing the block is as goes after: 1. The block should be flawless without cracks and corrosion (slotted blocks) Two. The fact that the block is not cracked at the point you rebuild it does not mean it has not embarked to crack. Trio. If there is any bowing then the block will require the crank carrier to be line bored. Four. Send for boring and honing. Five. Liquidate all core buttplugs and the rear engine plate. Then spend twenty minutes with a pressure washer to liquidate sediment and rust from inwards the block. Chemical cleaning can stain bearing faces, bores, etc. 6. Liquidate all the oil gallery corks (not leaving behind the petite conical gauze fitter behind the hydraulic chain tensioner), then pressure wash, preferably with detergent, all the oilways. 7. Substitute all the long studs, 8. While being substituted, the studs will rum sixteen to seventeen turns into the block, permitting for the domed cylinder head nut to tighten onto the head and not torque up a few threads above the spacer. Four studs are slightly longer than the others; this is for the engine lifting brackets.
The main contributing factor causing blocks to crack is due to the thermostat. When a car boils up you are told to let the engine coal down before topping up with coolant and that this stops the thermal shock which causes cracking. An eighty eight degrees C thermostat permits the engine to reach twelve degrees C less than boiling point before opening broad to permit the block to be swamped from one end by super cooled fluid from the radiator. In other words, your engine receives a thermal shock every time the thermostat opens.
To reduce this you can liquidate the puny back flow tag and drill another crevice the same size in the thermostat, permitting fluid to pass through the system and so help equalise the temperature of arguing and outgoing fluid. The engine will take three to four minutes longer to reach operating temperature but it helps stop the head gasket gargling.
Do not leave the thermostat out downright since the fluid will only circulate around the front of the engine mid this causes hot catches sight of. Make sure you use the correct thermostat on early pre-XJ6 engines as many of the early Trio.8 litre ones with cracks have been fitted with the smaller modem thermostat. Carburetted cars run well with seventy five degrees C thermostats drilled as above; fuel injected cars need an eighty eight degree C thermostat drilled to cancel out the warmth.
Cracks in the block may not always be apparent unless you have good eyesight and are specifically looking for them, so use crack test fluid. A non-Jaguar specialist would not necessarily notice them because they may not know to look for them.