Jaguar 1999 XJ V8 Sovereign 4.0 Auto LWB with 74k now valued below £2000, XJ27 engine has suffered all the hall marks of the Nikasil Bore liners legacy problem.


Hence I want the car the start first time on cranking so as not to wash away the oil on the piston rings as too many starts and all compression gone.


Have used thicker 10-40 semi synthetic oil at normal temps and kept a good fully charged battery to help over come the Nikasil problem.


Now looking to replace the plugs and to use a 4 prong terminal plug like those from Bosch as this may increase the igniting probability of the fuel mix projected more downward than the traditional J type like NGK types with codes BKR5EVXA orPFR5011E or IFR5N10.


Question to those experts out there
What is the typical clearance between plug end and piston head for a V8 using recommended plugs, is it 0.25mm (10 thou0 or is it usually more like 1mm (40 thou)


Have visited the Bosch and NGK web sites and got very mixed results.


Bosch seem to be narrowing their range of plugs. So I contacted them to ask for a compatible 4 prong plug or even any plug in there range. However Bosch sales told me they do not have a compatible plug even thou there site list a J type. So I researched further at sites and numbering systems for a plug. Found a Bosch Super 4 plugs that may fit but with reservation.


Super 4 with code FR78X 0 242 232 502. These have all the same specification of the NGK plugs but with 4 earth prongs / terminals. Heat range is OK at 7, and threads, reach, are correct at 14 x 1.25 and 19mm respectively. Gap is OK at 1.1mm. However the spark position =distance from the end of steel plug thread to positive terminal end is 4 mm whereas I want 3 mm so I could end fouling the piston heads if I don't have enough clearance.


Can anyone advise if using an extra 1mm on the spark position may foul the plugs onto the pistons and damage the heads.


Could I add an extra M14 dia x 1mm thick crush washer to the FR78X plugs to avoid any potential fouling


To get my compression back had to resort to adding a thimble or so of oil down the plug holes using a plastic tube to try to get the bores holding an oil seal to the piston rings again with some success.
Last question
Is there any additives one can use to stop the washing of oil off the bores on start up.

 

Aren't you over thinking this problem? Why not go with correct Denso or NGK iridium plugs? How frequently were you seeing the cylinder wash with newer, lower sulfur, gasoline (petrol) mixtures?

 

I have had those Bosch in my hand alongside the NGK.

Looking through the bubble pack, the Bosch have a longer reach. I don't care what their
book says. The reach is longer.

Use the NGK as intended.

AFTER the car has started, look into an additive called "Engine Restore".

 

Let me save you some trouble. These plugs don't 'fire' any better than a conventional plug.

The spark plug industry is as rife with marketing gobbledygook as the soap powder or beer business.

 

Thanks guys. My car won't start right now because of lost compression which happens every so often, say at least once a year or more, and I have to book it in a garage to get them to get the compression back for me before I can use it again. This is a bit of a pain to have to repeatedly do. I have the option to buy a replacement steel lined engine off a XJ8 or XK8 2001 with low mileage for reasonable cost around £750.
I note the point that the reach on the 4 prong may be too long, and I should keep using the recommended NGK J type.

 

Have you tried restoring the compression yourself by either/both of: adding oil to each cyl and/or repeated WOT cranking?

These each work on the S-Type 4.0 when suffering bore wash.

 

Yes I have tried twice myself to put a small measure of engine oil down a tube down plug holes into top of pistons but with no success. Tried to rotate a plastic tube to get closer to sides of pistons but these are 86 mm dia so I do not know how much I am getting to the sides. Got battery fully charged up and plugs and coils back in. Heard some degree of trying to start on say one cylinder.


WOT cranking =wide open throttle I presume


Are the piston head on the XJ27 concave and to what degree?


Key to it is
How much oil can I risk pouring in the plug holes without encountering an hydraulic problem on the cylinder head? I though no more than a tumble using a plastic tube of say 4mm or so and hand rotated cranks first before putting plugs and coils back and re-connecting battery and trying to re-start.

 

The amount usually quoted is 1/4 tsp, but I expect people add more without realizing it. You can then turn the engine over with WOT, which shuts the injectors off to distribute the oil.

 

You will likely need repeated WOT cranking, may even have to recharge battery. Keep tries fairly short so as not to overheat starter.

 

Just to recap
To get compression back on Nikasil AJ27 V8 1999 engine
1 Disconnect battery
2 Take out coils and plugs
3 Take a thimble full (1/4 table spoon) of engine oil and pour down a plastic tube via funnel, rotating tube to get oil onto side of pistons onto rings as far as possible, may manually rotate engine if some pistons at the top of their stroke which may help to distribute this small amount of oil. (must avoid using too much oil to avoid any hydraulic action of cylinder head that would damage engine).

Please comment if possible on whether the 1999 piston heads on the AJ27 engine are domed shaped with 4 notched in them and not concave and indented with a ridge round them as may be the case with some versions of the AJ26 1998 engines)


4 Please confirm or not: I could leave plugs out at this stage and reconnect battery and crank over using Wide Open Throttle (WOT) a few times in short bursts so as not to over heat starter motor, to avoid any more fuel injection and distribute this oil round rings at best as possible

5 Disconnect battery, put plugs (consider new ones as recommended for car) and put coils back and reconnect battery (have fully charged up)


6 Try to restart the engine at WOT to avoid any more fuel injection (several times if necessary to distribute the oil round rings).


How does that sound. Any further guidance before I go ahead. May try the WOT restart first since I have put oil down bores already.


if I get the back compression could consider buying a can of oil additive AMETECH ENGINE RESTORE to see if this keeps this problem away in the future and in future avoid running engine for short lengths or doing short journeys where the petrol injection at start up may have washed away oil seal and may cause restart / lack of compression problems.

 

I think you are overdoing the oil treatment. No matter what the shape of the piston top, the fact that it's a V8 means the oil will end up at the low edge of the piston and the rings will take car of distribution.
Using the starter to spin the engine at WOT will coat the walls, and it may not even be necessary. Leaving the plugs out will reduce the load on the starter and avoid fouling the plugs.
My owners manual has a procedure for starting a flooded engine. It merely says begin at WOT and the lift foot. There is no mention of using oil, as would be expected.

Finally, I wonder if your repeated incidences of bore wash might be an indication that the injectors are leaking fuel after the engine is shut off. You might want to obtain a fuel pressure gauge and connect it to the schrader valve on the fuel rail, then monitor the pressure drop after shut down.

 

Thanks guys for your valuable advice and comments. Don't process a pressure gauge to carry out any tests on the fuel injectors for possible leakage when the car is left standing, but thanks anyway.


I used WOT with all plugs, coils, battery in place, etc then varied accelerator from pressing it from WOT and then another start bust at normal position and another burst at WOT again to shut off the start-up fuel again .... Car started after 5 or 6 attempts of doing this and saved me a lot of time with any rerun of the procedure I have listed above for others to see.


Early the 8 coils and plugs looked OK when I took then out, some minor oil on coil ends on one of them so head cover seal not complete, bearing in mind on the RHS I have a couple of cover bolts missing due to broken thread inserts which I have lived with up to now.


I will probably buy some new plugs and fit them at some time.


I saw an interesting youtube video of AMETECH ENGINE RESTORE OIL ADDITIVE on a car with 2 out of 4 cylinders initially with low compression, where once the AMETECH was added to oil the 2 cylinders achieved pressure equal to the good two, so I may opt to get some in near future, so Thanks again for that tip. I hope it will offset any future problem on this Nikasil lined engine.


I really not looking to spend any major bucks on this car, although had considered getting a later 2001 replacement engine. Expect at 76k this engine has some way to go still, but I expect it will give me more trouble later on.

 

The WOT cranking done by several S-Type 4.0 guys just worked. Didn't add oil, didn't remove plugs at all. Adding the oil is likely to be faster and better but appears unnecessary - much kinder on the starter, though.

The idea is that you restore compression then as soon as it tries to start use about 2/3 or 3/4 throttle briefly.

 

Thanks for the information. I will bear this in mind, to use just WOT, the next time I loose compression due to too many short journeys or repeated starts. Good post.

 

Quote:

Originally Posted by plums

I have had those Bosch in my hand alongside the NGK.

Looking through the bubble pack, the Bosch have a longer reach. I don't care what their
book says. The reach is longer.

Use the NGK as intended.

AFTER the car has started, look into an additive called "Engine Restore".

The above quote is the opposite to what I can observe. I have both plugs in my hand. The Bosch Super 4 shows around 1mm less in total length and from base of thread to earth terminal end/s shows around 1mm less in total length than the recommended NGK J shaped plug for the AJ27 V8 engine.


So the Bosch super 4 plug easily fits into the XJ27 engine and will not foul the piston heads.

 

Use the best Iridium plugs you can afford.

 

'Use the best Iridium plugs you can afford'


The Iridium - Plat just extend life 100k miles and may be self cleaning to an extent compared to the basic copper core plugs which only go to 30k miles.


NGK recommend for XK8 (96-->05) 4.0 AJ27 iridium Platinum IFR5N10 which I have been using on car. Spec No. : IFR5N10 / Stock No. : 7866 NGK Iridium tipped types Spark Plugs IFR5N10
Design Symbols used in NGK Spark Plugs I - Plug Type: Iridium Platinum F - Metal Shell Size: ? 14, 19 mm (3/4") Reach, 16 mm (5/8") Hex. Heat Rating Numbers : 5 Gap .040" (1.02mm)


Bosch do not recommend Iridium plugs any plug at all for XJ8.


However on some ebay sites give the following suitable 4501 plug for JAGUAR XJ8 (1999) 4.0LV8 and JAGUAR XK8 (1999) 4.0LV8
Spec No 4501 / FGR8DQI Iridium Platinum, 14mm Thread Size, 19mm (3/4") Reach, 5/8" (16mm) Hex Size, Gasket Seat, Interference Suppression Resistor, Surface Air Gap Plug, 4 Ground Electrodes, Iridium-Platinum Fused Center Electrode, .040" (1.02mm) Gap, Heat Range 8


Bearing in mind Bosch use a different heat scale 7 - 8 is around the right heat rating at the NGK 5 rating for the XJ27, so these later plugs look a good possibility to use for the XJ27 engine. The gap 1.02mm is the same as the NGL IFR5N10


The older AJ26 engines had a larger 1.3 mm gap like on PFR5G 13E. NGK officially recommend for XJ27 for XJ8 97-03 AJ27 4.0 Platinum tipped types Spark Plugs
PFR5G-11E / Stock No. : 3000 where p=plat F - Size: 14, 19 mm (3/4") Reach, 16 mm (5/8") Hex. R - Resistor Heat Rating 5 G - Firing End Construction: Fine Wire Nickel Alloy Centre Electrode 11 - Spark GAP: 1.1 mm (.044") E - Spark GAP: Special Resistance.


But I think I may look at buying a Bosch 4501 and do visual comparison to the plugs I am replacing the IFR510N at some point in the future.

 

Ken-

Agonizing over spark plug selection to address a bore wash issue is a complete waste of time. Use the recommended plug and alter your driving habits to avoid repeat bore wash events.