Discussion
There is a buying guide somewhere in the Jaguar section of PH, but basically Nikasil bores on 4L & then 3 generations of timing chain tensioners which range from soft as chocolate to decent. The 4.2 had fixed a lot of the problems over the 4L though. Depends what it is installed in as well.
pixieporsche said:
Interesting, I've bee told the 4.2 is the weak one! Didn't they have to stagger the bores?
I think you're talking about the classic straight six Jaguar XK engine in 4.2 litre guise, rather than the 4 litre and 4.2 litre V8 engine fitted to the later Jaguar XK8?I have limited knowledge of the old XK, but have heard that the 4.2 can be prone to develop cracks between the cylinders. I think the engine used in the Series 3 cars is stronger than the version used in the Series 2. I'm sure someone with more knowledge of these engines will come along soon.
The Nikasil/tensioner issues are problems with some versions of the V8 engine used on much later cars.
Durable, low stressed engine should go 100k without problems if cared for. Generally very quiet and smooth with lots of mid range torque but some vibration at high rpm especially noticable on manuals.
All XK engines on 2 or 3 carburettors and conventional points/mechanical distributor with exception of post 1979 Series III. Manufactured in 2.4l, 3.4l, 3.8l and 4.2l capacities.
Cracks between the bores usually only happens on the 4.2, headgaskets occasionally fail, oil leaks from the rear crank seal common, siezed head studs, low oil pressure indicates main bearing wear or failing return valve in oil pump or faulty sender unit (min 40 psi hot). Upper timing chain needs tension setting carefully otherwise may cause excessive noise/wear, overheating leads to dropped valve guides which cause knock, aluminium head water gallery corrosion, core plugs corrode and fail, worn/hardened valve stem oil seals cause blue smoke on overun.
Revisions to injected 4.2 fitted in the S3 cars make it the best one - especially with regards to fuel consumption IMO.
If it's quiet, has good hot oil pressure and not leaking anything from anywhere and shows no inclination to overheat then should be OK.
All XK engines on 2 or 3 carburettors and conventional points/mechanical distributor with exception of post 1979 Series III. Manufactured in 2.4l, 3.4l, 3.8l and 4.2l capacities.
Cracks between the bores usually only happens on the 4.2, headgaskets occasionally fail, oil leaks from the rear crank seal common, siezed head studs, low oil pressure indicates main bearing wear or failing return valve in oil pump or faulty sender unit (min 40 psi hot). Upper timing chain needs tension setting carefully otherwise may cause excessive noise/wear, overheating leads to dropped valve guides which cause knock, aluminium head water gallery corrosion, core plugs corrode and fail, worn/hardened valve stem oil seals cause blue smoke on overun.
Revisions to injected 4.2 fitted in the S3 cars make it the best one - especially with regards to fuel consumption IMO.
If it's quiet, has good hot oil pressure and not leaking anything from anywhere and shows no inclination to overheat then should be OK.
Jaguar steve said:
and not leaking anything
Most XKs will leak a bit of oil, it helps rust proof the bottom of the car. 
It didn't remain in production for over 40 years for no reason. Powering everything from half the Le Man winners of the 50s to light tanks. It has to be a good candidate for any list of all time great engines.
They are also in cheap and plentiful supply.
Jaguar steve said:
Durable, low stressed engine should go 100k without problems if cared for. Generally very quiet and smooth with lots of mid range torque but some vibration at high rpm especially noticable on manuals.
All XK engines on 2 or 3 carburettors and conventional points/mechanical distributor with exception of post 1979 Series III. Manufactured in 2.4l, 2.8L 3.4l, 3.8l and 4.2l capacities.
Cracks between the bores usually only happens on the 4.2, headgaskets occasionally fail, oil leaks from the rear crank seal common, siezed head studs, low oil pressure indicates main bearing wear or failing return valve in oil pump or faulty sender unit (min 40 psi hot). Upper timing chain needs tension setting carefully otherwise may cause excessive noise/wear, overheating leads to dropped valve guides which cause knock, aluminium head water gallery corrosion, core plugs corrode and fail, worn/hardened valve stem oil seals cause blue smoke on overun.
Revisions to injected 4.2 fitted in the S3 cars make it the best one - especially with regards to fuel consumption IMO.
If it's quiet, has good hot oil pressure and not leaking anything from anywhere and shows no inclination to overheat then should be OK.
There was a 2.8 in the XJ Series 1 as well Steve. On 4.2s I've done head gaskets & a few chains when they were current, but they have generally been OK afterwards. Although getting the head off has been a huge pain, as it corrodes to the studs.All XK engines on 2 or 3 carburettors and conventional points/mechanical distributor with exception of post 1979 Series III. Manufactured in 2.4l, 2.8L 3.4l, 3.8l and 4.2l capacities.
Cracks between the bores usually only happens on the 4.2, headgaskets occasionally fail, oil leaks from the rear crank seal common, siezed head studs, low oil pressure indicates main bearing wear or failing return valve in oil pump or faulty sender unit (min 40 psi hot). Upper timing chain needs tension setting carefully otherwise may cause excessive noise/wear, overheating leads to dropped valve guides which cause knock, aluminium head water gallery corrosion, core plugs corrode and fail, worn/hardened valve stem oil seals cause blue smoke on overun.
Revisions to injected 4.2 fitted in the S3 cars make it the best one - especially with regards to fuel consumption IMO.
If it's quiet, has good hot oil pressure and not leaking anything from anywhere and shows no inclination to overheat then should be OK.
I found this:
http://www.jagweb.com/jagworld/xk-engine/index.htm...
Very interesting. I'm not sure how true it is, but they say that the early engines are fine but that in the '70's the equipment to make the engine was wearing out, and 'value led engineering' caused them to relax the tolerances. This is when problems started.
See specifically page 5 '70's decline'
http://www.jagweb.com/jagworld/xk-engine/index.htm...
Very interesting. I'm not sure how true it is, but they say that the early engines are fine but that in the '70's the equipment to make the engine was wearing out, and 'value led engineering' caused them to relax the tolerances. This is when problems started.
See specifically page 5 '70's decline'
Edited by varsas on Monday 16th May 08:52
4.2 and 3.4 are great if they've been well looked after. If not, then there will be pain if you ever have to get the head off. The long studs corrode down in the bottom of the block where they pass through the coolant and can snap.
2.8 has a reputation for holing pistons, which is NOT a myth. I found out the hard way that they are still as capable as ever of pulling this trick.
Parts are plentiful, and there's lots of specialists that can rebuild them. There's also quite a few of the military versions with stronger heads and valve guides on the market now.
Regards,
Rich
2.8 has a reputation for holing pistons, which is NOT a myth. I found out the hard way that they are still as capable as ever of pulling this trick.
Parts are plentiful, and there's lots of specialists that can rebuild them. There's also quite a few of the military versions with stronger heads and valve guides on the market now.
Regards,
Rich
richw_82 said:
Parts are plentiful, and there's lots of specialists that can rebuild them. There's also quite a few of the military versions with stronger heads and valve guides on the market now.
Regards,
Rich
The J72, military version, of the head also has self lapping valves. Regards,
Rich
The machining of the blocks is also supposed to be better on these engines, the military didn't like the cost reductions processes that BL's accountants foisted on the rest of Jaguar.
tr7v8 said:
Jaguar steve said:
Durable, low stressed engine should go 100k without problems if cared for. Generally very quiet and smooth with lots of mid range torque but some vibration at high rpm especially noticable on manuals.
All XK engines on 2 or 3 carburettors and conventional points/mechanical distributor with exception of post 1979 Series III. Manufactured in 2.4l, 2.8L 3.4l, 3.8l and 4.2l capacities.
Cracks between the bores usually only happens on the 4.2, headgaskets occasionally fail, oil leaks from the rear crank seal common, siezed head studs, low oil pressure indicates main bearing wear or failing return valve in oil pump or faulty sender unit (min 40 psi hot). Upper timing chain needs tension setting carefully otherwise may cause excessive noise/wear, overheating leads to dropped valve guides which cause knock, aluminium head water gallery corrosion, core plugs corrode and fail, worn/hardened valve stem oil seals cause blue smoke on overun.
Revisions to injected 4.2 fitted in the S3 cars make it the best one - especially with regards to fuel consumption IMO.
If it's quiet, has good hot oil pressure and not leaking anything from anywhere and shows no inclination to overheat then should be OK.
There was a 2.8 in the XJ Series 1 as well Steve. On 4.2s I've done head gaskets & a few chains when they were current, but they have generally been OK afterwards. Although getting the head off has been a huge pain, as it corrodes to the studs.All XK engines on 2 or 3 carburettors and conventional points/mechanical distributor with exception of post 1979 Series III. Manufactured in 2.4l, 2.8L 3.4l, 3.8l and 4.2l capacities.
Cracks between the bores usually only happens on the 4.2, headgaskets occasionally fail, oil leaks from the rear crank seal common, siezed head studs, low oil pressure indicates main bearing wear or failing return valve in oil pump or faulty sender unit (min 40 psi hot). Upper timing chain needs tension setting carefully otherwise may cause excessive noise/wear, overheating leads to dropped valve guides which cause knock, aluminium head water gallery corrosion, core plugs corrode and fail, worn/hardened valve stem oil seals cause blue smoke on overun.
Revisions to injected 4.2 fitted in the S3 cars make it the best one - especially with regards to fuel consumption IMO.
If it's quiet, has good hot oil pressure and not leaking anything from anywhere and shows no inclination to overheat then should be OK.
you're right. Forgot about the 2.8 - probrably the least loved version due to it's tendencies to burn out pistons when driven hard after long periods on light loads.2.8's don't do too well after 9,000 miles of thrashing up and down motorways while drinking cheap unleaded.
Credit to their strength though, I lost the piston at J21 M1, and it made it back to my house just off J29 on the five it had left.
To date, my Series 1 has never left me stranded by the road.
Credit to their strength though, I lost the piston at J21 M1, and it made it back to my house just off J29 on the five it had left.
To date, my Series 1 has never left me stranded by the road.
I should have said from the outset I'm talking about the XK engine not the V8 engine fitted to the XK8. 
Thank you all for your advice. What oil pressure should a 4.2 be running at when warm and idling?
ETA - question answered, thank you Jaguar Steve.
ETA2 - if the worst comes to the worst what sort of figure am I looking at to rebuild a 4.2? I've been told it's about a £4,000 job, is this correct?
Thank you all for your advice. What oil pressure should a 4.2 be running at when warm and idling?
ETA - question answered, thank you Jaguar Steve.
ETA2 - if the worst comes to the worst what sort of figure am I looking at to rebuild a 4.2? I've been told it's about a £4,000 job, is this correct?
Edited by pixieporsche on Monday 16th May 12:15
Jaguar steve said:
Blimey you're right. Forgot about the 2.8 - probrably the least loved version due to it's tendencies to burn out pistons when driven hard after long periods on light loads.
Yes, but it's not the above circumstances that cause the damage. you're right. Forgot about the 2.8 - probrably the least loved version due to it's tendencies to burn out pistons when driven hard after long periods on light loads.It is caused by a combination of setting the carb mixture too lean and then the advance vacuum pipe either vibrating loose from the rubber adapter under the inlet manifold, or the adapter itself splitting. The 2.8 engine ran a double advance/retard capsule on the distributor. This causes instant pre-ignition at high revs causing a hot spot in the centre of the piston at the vicinity of the spark plug.
The piston that usually goes is the one nearest the vacuum take off, as it runs even leaner due to failure of the pipe.
This was once again an appalling lack of development on Jaguar's psrt. They knew about this fault and did virtually nothing to fix it. I remember replacing 3 engines in 1 week under warranty due to this!!
The sad thing is that the 2.8 is the sweetest engine they have ever made. Had they fitted it with injection and electronic ignition it would have been superb.
Incidentally, the answer if you want to run one now is to fit a 123 distributor, platinum plugs, and make sure the vacuum take off pipes are permanently blocked up. You can then use the variable settings on the distributor to give you the required advance.
J
jith said:
Jaguar steve said:
Blimey you're right. Forgot about the 2.8 - probrably the least loved version due to it's tendencies to burn out pistons when driven hard after long periods on light loads.
Yes, but it's not the above circumstances that cause the damage. you're right. Forgot about the 2.8 - probrably the least loved version due to it's tendencies to burn out pistons when driven hard after long periods on light loads.It is caused by a combination of setting the carb mixture too lean and then the advance vacuum pipe either vibrating loose from the rubber adapter under the inlet manifold, or the adapter itself splitting. The 2.8 engine ran a double advance/retard capsule on the distributor. This causes instant pre-ignition at high revs causing a hot spot in the centre of the piston at the vicinity of the spark plug.
The piston that usually goes is the one nearest the vacuum take off, as it runs even leaner due to failure of the pipe.
This was once again an appalling lack of development on Jaguar's psrt. They knew about this fault and did virtually nothing to fix it. I remember replacing 3 engines in 1 week under warranty due to this!!
The sad thing is that the 2.8 is the sweetest engine they have ever made. Had they fitted it with injection and electronic ignition it would have been superb.
Incidentally, the answer if you want to run one now is to fit a 123 distributor, platinum plugs, and make sure the vacuum take off pipes are permanently blocked up. You can then use the variable settings on the distributor to give you the required advance.
J
Of course detonation is the cause of melting 2.8 pistons - I should have said a high build up of carbon deposits on the piston crowns from a long period at light load was just a contributory factor towards detonation, not the cause itself.
Blame lack of coffee...
jith said:
Yes, but it's not the above circumstances that cause the damage.
It is caused by a combination of setting the carb mixture too lean and then the advance vacuum pipe either vibrating loose from the rubber adapter under the inlet manifold, or the adapter itself splitting. The 2.8 engine ran a double advance/retard capsule on the distributor. This causes instant pre-ignition at high revs causing a hot spot in the centre of the piston at the vicinity of the spark plug.
The piston that usually goes is the one nearest the vacuum take off, as it runs even leaner due to failure of the pipe.
This was once again an appalling lack of development on Jaguar's psrt. They knew about this fault and did virtually nothing to fix it. I remember replacing 3 engines in 1 week under warranty due to this!!
The sad thing is that the 2.8 is the sweetest engine they have ever made. Had they fitted it with injection and electronic ignition it would have been superb.
Incidentally, the answer if you want to run one now is to fit a 123 distributor, platinum plugs, and make sure the vacuum take off pipes are permanently blocked up. You can then use the variable settings on the distributor to give you the required advance.
J
BullsIt is caused by a combination of setting the carb mixture too lean and then the advance vacuum pipe either vibrating loose from the rubber adapter under the inlet manifold, or the adapter itself splitting. The 2.8 engine ran a double advance/retard capsule on the distributor. This causes instant pre-ignition at high revs causing a hot spot in the centre of the piston at the vicinity of the spark plug.
The piston that usually goes is the one nearest the vacuum take off, as it runs even leaner due to failure of the pipe.
This was once again an appalling lack of development on Jaguar's psrt. They knew about this fault and did virtually nothing to fix it. I remember replacing 3 engines in 1 week under warranty due to this!!
The sad thing is that the 2.8 is the sweetest engine they have ever made. Had they fitted it with injection and electronic ignition it would have been superb.
Incidentally, the answer if you want to run one now is to fit a 123 distributor, platinum plugs, and make sure the vacuum take off pipes are permanently blocked up. You can then use the variable settings on the distributor to give you the required advance.
J
t.Light loads or deposits, followed by prolonged hard work kill it. I should know I did it, six months ago.
I did 9,000 miles in mine, driving it every day roughly 1200 miles per month. It didn't have a vac leak or run lean, and still hadn't when I got home on a half dead engine. You don't live with one every day and not notice if your engine is sick.
The damage on my engine was as expected; the hole was at the crown of the piston. It was on the front cylinder, next to the chains (No 6) and nowhere near the vac take off, which for the distributor is off the back carb. The only ones off the manifold are heater system, vacuum tank, and brakes.
All pistons showed excessive deposits of God knows what, and signs of plug fouling, which had only started showing after using "Fuelsave" unleaded - which to be honest is little better than gnats piss. Likely the deposit was the 'special coating' they bang on about that supposedly reduces friction.
I got the car on the motorway, and bye bye piston, after roughly 90 miles into a tank of Fuelsave. I was annoyed mightily (and still am) as it was the sweetest XK engine I've ever had. With the manual gearbox behind it, it was a delight.
Rich
richw_82 said:
jith said:
Yes, but it's not the above circumstances that cause the damage.
It is caused by a combination of setting the carb mixture too lean and then the advance vacuum pipe either vibrating loose from the rubber adapter under the inlet manifold, or the adapter itself splitting. The 2.8 engine ran a double advance/retard capsule on the distributor. This causes instant pre-ignition at high revs causing a hot spot in the centre of the piston at the vicinity of the spark plug.
The piston that usually goes is the one nearest the vacuum take off, as it runs even leaner due to failure of the pipe.
This was once again an appalling lack of development on Jaguar's psrt. They knew about this fault and did virtually nothing to fix it. I remember replacing 3 engines in 1 week under warranty due to this!!
The sad thing is that the 2.8 is the sweetest engine they have ever made. Had they fitted it with injection and electronic ignition it would have been superb.
Incidentally, the answer if you want to run one now is to fit a 123 distributor, platinum plugs, and make sure the vacuum take off pipes are permanently blocked up. You can then use the variable settings on the distributor to give you the required advance.
J
BullsIt is caused by a combination of setting the carb mixture too lean and then the advance vacuum pipe either vibrating loose from the rubber adapter under the inlet manifold, or the adapter itself splitting. The 2.8 engine ran a double advance/retard capsule on the distributor. This causes instant pre-ignition at high revs causing a hot spot in the centre of the piston at the vicinity of the spark plug.
The piston that usually goes is the one nearest the vacuum take off, as it runs even leaner due to failure of the pipe.
This was once again an appalling lack of development on Jaguar's psrt. They knew about this fault and did virtually nothing to fix it. I remember replacing 3 engines in 1 week under warranty due to this!!
The sad thing is that the 2.8 is the sweetest engine they have ever made. Had they fitted it with injection and electronic ignition it would have been superb.
Incidentally, the answer if you want to run one now is to fit a 123 distributor, platinum plugs, and make sure the vacuum take off pipes are permanently blocked up. You can then use the variable settings on the distributor to give you the required advance.
J
t.Light loads or deposits, followed by prolonged hard work kill it. I should know I did it, six months ago.
I did 9,000 miles in mine, driving it every day roughly 1200 miles per month. It didn't have a vac leak or run lean, and still hadn't when I got home on a half dead engine. You don't live with one every day and not notice if your engine is sick.
The damage on my engine was as expected; the hole was at the crown of the piston. It was on the front cylinder, next to the chains (No 6) and nowhere near the vac take off, which for the distributor is off the back carb. The only ones off the manifold are heater system, vacuum tank, and brakes.
All pistons showed excessive deposits of God knows what, and signs of plug fouling, which had only started showing after using "Fuelsave" unleaded - which to be honest is little better than gnats piss. Likely the deposit was the 'special coating' they bang on about that supposedly reduces friction.
I got the car on the motorway, and bye bye piston, after roughly 90 miles into a tank of Fuelsave. I was annoyed mightily (and still am) as it was the sweetest XK engine I've ever had. With the manual gearbox behind it, it was a delight.
Rich
t.I worked on these cars when they were new, do you understand that? The description I gave was dead accurate, and the fault was finally admitted by the factory themselves. One of the cars I changed the engine on was only 6 weeks old and had no carbon build up whatsoever.
Just to enlighten your clearly limited knowledge, as already stated, there are 2 vacuum pipes, one from the top of the carb and one underneath the manifold; one advances the capsule, the other retards. The one underneath cannot be seen when looking into the engine bay, hence the reason they were frequently missed and damage done. The worst aspect of this was the fact that the pipe was hanging from the manifold unsecured, no clips, nothing, just a push fit, and could fall off very easily.
Now what did happen, is that some people thought that if you simply fitted a 4.2 distributor with a single advance that this would cure the problem. In actual fact it was totally unsuited to the 2.8 cam and piston set up. If you have a distributor with only one vacuum take off on the capsule it is the wrong distributor.
This engine is obviously sensitive to timing errors resulting in piston damage. Your piston was holed in the centre because that is where the hot spot is created by the spark plug during the pre-ignition interval. But the damage to your piston was undoubtedly caused by the crap YOU poured in the tank, and probably also because the engine was not properly set up in the first place.
J
pixieporsche said:
I should have said from the outset I'm talking about the XK engine not the V8 engine fitted to the XK8.
I thought you did, the title seemed perfectly clear, the XK Engine is an inline 6 cylinder beauty launch to an incredulous world in 1949. There was a proposed 4 cylinder version too but it never made it past the prototype stage.The modern XK8 and XK run AJ26... and onwards engines.
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