Daniel's Jaguar XJ6 Survival Guide-Blog My experiences and suggestions on XJ6 ownership


Transplant Update

Man, it's been a while since I posted! Time to get on with things!

In my last edition I spoke of a V12 engine transplant for my XJ6 from a donor V12 VDP. Unfortunately said project was on hold all winter long but spring is upon us and the time has come to commence with my work!

I've bypassed the fuel system in the original V12 donor car and run the engine from a clean tank and pump right off the side of the engine bay. This doesn't allow for any driving but does ensure that any fuel-related issues are eliminated for testing purposes. Essentially a pump and filter are connected in series and attached to the fuel rail. The intake of the pump takes fuel from a fuel container and the return line from the pressure regulator feeds back to said tank in a circulating loop. Running in this fashion eliminated a number of troubles I was having with blocked up change-over valves, dirty tanks, broken lines, etc.

Now with the engine burning clean fuel I've been able to establish perfect operation of all but two cylinders which have extremely low compression. A dry compression test revealed about 90PSI on the affected cylinders while the others were around 210PSI. A wet compression test brought the offending pair to the proper level and thus the piston rings and/or liner must be damaged. The piston rings could also be stuck but none of the usual treatments (solvent soaks, steam cleaning, running, etc) have made much difference aside from simply making the engine run cleaner overall.

I'll be soon to post some pictures of my example test setup so others can see what I'm doing. Within a couple of weeks the engine is due to come out of the car and get opened up. I plan on replacing the piston rings for all twelve cylinders and performing a light bore honing.  With new bearings and a general cleanup the engine will be as good as new!


Of transplants.

Well it's been a while! It seems I've been spending lots of time on the Jags and not on my blog writing updates on my progress.

In the time since the last post I've experienced a blown head-gasket, taken the '85 off the road, removed the head, disassembled the head, and obtained a complete 1985 V12 VDP (Vanden Plas) with working drive-train for parts.

On removal of the head from the XK motor in the '85 I found what I suspected in the past to be true: the No.2 exhaust valve is burned and beginning to crack. Luckily it didn't fall apart and do damage to anything else in the engine.  Looking at the cost of reconstituting this cylinder head I started to look for cheap parts cars around here that I can use in the process. I found myself a nice V12 VDP for very cheap and got it towed to my place. I can't get the title for the car so I've decided to use the V12 in place of my XK motor which is an inline six. All of the parts from one car fit the other so this should be a reasonably straightforward process although lengthy.

The XK engine, once put back together, will probably end up in my Volvo 245DL and make it into quite a smooth and powerful Volvo! Not to mention, the engine bay won't look like a cavern.

The V12 engine had sat for a long time, maybe six or seven years, and so needs some definite cleaning and tuning. I've found the compression to be pretty good all around except on cylinders 3A and 4A. Chances are I'm not lucky enough for the piston rings to simply be stuck. Most likely the rings are worn or damaged somehow and I'll have to remove the A-bank head and open the bottom of the engine so I can pull those pistons out and change the rings. Luckily it isn't too expensive a job and I can probably do it within a day's work.

I was amazed when I obtained the V12 car how badly the previous owner had configured the engine. He wanted to change the spark plugs and so removed the intake manifolds, fuel injection system, throttle bell-crank, distributor, vacuum lines, and A/C compressor! Really all that's necessary is to move the A/C compressor over, remove the throttle bell-crank, and move some wiring aside. The re-assembly was performed horribly; there were nuts and bolts missing on important things like injector clamps, intake manifold runners, etc. The 6A injector was missing its O-ring between it and the manifold allowing air to pass right by! The vacuum lines were mostly disconnected or connected all wrong. There were electrical connectors going to all the wrong places. There's no chance it would ever have run in that state yet they were trying anyhow.

Within three hours' time I had figured out what was necessary to make it run and put it together. I found all the missing hardware and installed it to prevent any leaks. Even after having sat for so many years it all fired up with some coaxing but it really sounded horrible. A few days later and now it runs really well. No smoke, no steam, just clean burning and perfectly smooth idle!

I took the old car for a spin up and down my road and I've found that the transmission refuses to up-shift until the red-line so I'm going to assume the modulator is stuck. On the GM THM400 transmission used in these cars, the shift-points are controlled by sensing engine vacuum against vehicle speed instead of sensing engine throttle position against vehicle speed. If the modulator is disconnected or stuck the transmission will be reading "full-throttle" continuously and shift as mine does. Hopefully I can fix or replace the modulator and return it to normal operation.

I'm really glad to be moving into V12 land and will try and update my progress with this one as it's really a cool project!


Look for the obvious!

This entry looks at my work with other XJ6s than my own. Since I love working with Jaguars I end up repairing/maintaining these cars for my friends and customers.

The XJ6 in question today is a 1986 Vanden Plas; essentially the same car as mine but with uprated interior and trim. The owner has so far spent a great deal of money on this car in acquiring it and keeping it on the road; I would say the main expense was from mechanics not familiar with these cars. The car was in use as a daily-driver and is really in excellent condition externally. The interior has water damage in the center console and a fallen headliner, most likely due to a moon-roof leak or similar problem.

The owner of this car parked it one day because the charging system had stopped working. The car would run only on a freshly charged battery which would only discharge as the car was used. Since he thought a new alternator and the labor to install it would be prohibitively expensive the owner parked the car for whatever reason instead of repairing the fault. It sat this way for two years until he met me and found out I was able to work on his car.

After a cursory glance under the bonnet I revealed to him that his alternator belt simply had broken and gone missing. $13 later and the charging system was operating perfectly. This is all fine and well except the car has numerous new problems which are a result of sitting around for two years unused. The engine would not start, the interior is getting rather stuffy and the leather stiff. The brakes need a good baking and the car is extremely dirty from junk off the trees coating it in the rain.

I found one of the fuel tank change-over valves was stuck, the fuel pump stuck as well. Luckily these can be woken up with a few sharp blows using a large drift. After solving the fuel problem I've found that the climate control system refuses to function, the coolant thermostat is stuck open, the breather cap and airflow meter pipe are cracked and leaking, and most of the window switches don't work! The cracked pipes have probably been that way for over five years but the others are due to the car not being used.

I'm so happy this person has decided to bring his favorite car back to life and use it again instead of leaving it to rot! If he'd had someone at least glance in the engine bay he would have been so far ahead of where he's at now! I essentially write this post to remind people not to think the worst and give up on their cars, or any other thing for that matter, as the problem is often simpler than you expect and just needs some careful diagnosis.

I'll follow up with before/after pictures of the car when I clean the muck off and give it a good detailing. Maybe even a video of her driving along would be in order!

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Braking the beast in motion.

Today marks the day of a new era; that of restored stopping power to compensate for that lovely XK pulling power and also to no longer worry how little of my front brakes is left.

When I bought the 85 XJ6 I realized early on that the front calipers were getting old and the pads were fairly thin. A few thousand kilometers later and the pads are running right to nothing. I was just able to get my hands on a set of freshly rebuilt calipers and pads (there goes $460!).

I haven't installed the new calipers yet (doing that later today) but I like the look of them so much I thought I'd put up a posterity post with some pictures to show off the pretty new car parts. These are remanufactured original Girling calipers from A1-Cardone. I've never purchased anything from Cardone before so I was taking a chance not knowing of their quality.

I'm pleased at least on outward appearances so far: The calipers are perfectly clean, powder coated (not every place will do this part), lightly coated in oil, and are properly assembled with new pistons, seals and clips. They come with a complete set of retaining hardware also lightly oiled in a sealed plastic bag and clear instructions. The instructions are not specific to this model but just very generic, dealing with disc brakes in general.

I also have a set of Raybestos Professional grade pads; again, I've not tried these before so we'll see how they do.

I'll write a later post with pictures of the installation and the old parts removed. I'll update on how the car performs in terms of braking. Presently the braking power is just fine but it is uneven and kind of lumpy. The car likes to pull to the side at certain braking forces and has sort of a stepped response: characteristic of worn or sticking calipers that aren't in balance anymore.

Here's the car part pornography:Brake Calipers


Cylinder head giving up.

So here is a problem I didn't see coming on an old XK engine: Cracks spreading down the middle of the cylinder head between the spark plugs.

Since shortly after I bought the 85 XJ6 I noticed the core plugs in the head like to weep a bit of coolant. I knocked them in a bit further as it looked as if they'd been working out of place. The leaks are very slow now but still apparent. I've driven it this way for quite a while with no ill effects but recently noticed that there are actually very fine cracks spreading along between the core plug holes. These cracks could have been there for quite some time, I'm really not sure.

I've never heard of heads cracking on the XK motor, though the early 4.2L blocks are known to crack between cylinder bores. A revision to the block later on involved slots machined into it between bores to reduce the likelihood of cracks forming.

So far I haven't made any particular plans to deal with the cracked cylinder head except for finding a replacement when I can and making a fully re-conditioned head out of the new and old. Until then who knows how long it'll last, perhaps these cracks have been there for years!

I'd love if anyone could comment on this, especially if you've seen this happen on this type of engine.


Those damned fuses…

Here's a little quip about something that is really irritating but not particularly hard to fix. I just procrastinate about it because it's only an intermittent problem and a bit of fiddling puts it at bay for awhile longer each time.

If you have an XJ Series III you'll notice there are two fuse panels inside, one under each end of the dash. There's also a panel under the bonnet on the wing (under the hood on the fender) which is for the headlamps in particular. There are also in-line fuses all about the car hidden under panels and covers.

The in-line fuses seem to cause relatively little trouble (I've never had to fix one on my Jags). The panels under the dash are the biggest problem in these cars.

The dash fuse panels use the classic tubular fuses seen on most old cars. They are held in with brass clips which become tarnished over time. The clips also lose their spring tension against the fuse. The result is a bad or intermittent connection. On my 83 the dash instruments like to drop off because of their fuse being loose. The 85 likes to give up the interior lights and door lock system. Wiggling the fuses and pushing them up and down will usually restore operation in a pinch. One can also squeeze the contacts together using pliers to make the fuse fit more tightly.

After a few years of fiddling with these problems and not really performing a proper fix on my cars I've decided on a method I'm going to use to try and solve the problem once and for all. Of course one good way to deal with this is to fit modern fuses but I don't feel like going that far with it right now.

It should be possible to fit a small wire brush to a rotary tool such as a Dremel and use it to remove heavy corrosion or deposits on the fuse contacts. If there are no heavy deposits and just a light coating, I recommend using a small buffing cylinder or even a cotton swab (if you're capable of running the rotary tool at low speeds). Dip this buffer or cotton swab in a polishing compound or liquid such as Brasso and use it to polish the contacts. It will completely remove all tarnish and leave you with bare metal. The importance of having a smooth surface is in having a lot of contact area between the contacts and the fuses. If this surface is rough, it is more likely to oxidize and to make a bad connection. Many a person has sanded relay contacts or connector terminals with rough sand paper and realized a good connection that only lasted a short while.

After wire-wheeling and polishing the contacts, they should look very shiny and bright where they touch the fuses. A further safe-guard against chronic corrosion would be to coat the contacts in dielectric grease. This will prevent oxygen from reaching the contacts so easily and also keep out moisture and contaminants. Once the contacts are coated, fit the fuses and everything should work well for a very long time.

I've performed this treatment on numerous connectors so I know it works; I just haven't applied it to fuses yet.

I'll post back on my results and include a couple of pictures showing the difference between old tarnished contacts and nice fresh ones.

If the fuses look tarnished it would be beneficial to polish their end-caps too; but be careful, they easily break.



Get it out for a spin!

So I thought I'd give a little quip about something a lot of us Jaguar owners are pretty particular about: getting the Jag(s) out for a drive fairly often.

Not just that driving Jaguars is a great experience; it's good for the car. This applies to any car but it seems like the Jag is even more fussy about not getting taken out at least from time to time. (This is especially true of older cars which have aged parts, old hardened rubber, etc.)

Since I bought my 85 series III I've noticed a steady improvement in its characteristics ever since I started driving it. At the get-go it was running laughingly; it stumbled, misfired, didn't feel right, it didn't smell right, it just wasn't too hot. Over the last few thousand kilometers everything's been smartening up, though new problems appear as something which sat around is put to use again.

On my 83 the brake system failed due to being left to sit for too long. Water gets into the brake fluid from non-use (using the brakes heats things up and gets the water out a bit more). The master cylinder failed and the calipers got rusty and stuck. This is an awful experience as calipers for the Jags are expensive and somewhat difficult to replace if you have to do the ones in the rear.

Other problems to expect from not running the car are:

  • Electrical gremlins (switch contacts build an oxide layer, same in relays)
  • Engine issues (fuel gets stale and can build an awful varnish inside the system, moisture builds inside the engine in some climates, etc)
  • The climate control system and A/C get wonky or stop working all together (A/C needs to be operated periodically to keep the lubricant up in the system and keep the seals happy. The climate control flaps can get stuck if they sit closed too long and don't open so nicely).
  • Moisture building in the exhaust system will make it rust (engine heat during operation keeps this out).
  • Bearings and suspension supports can get sticky, bound, etc (the grease isn't getting circulated in the bearings enough and water can slowly cause damage (though it shouldn't if the seals are good and there's enough grease in place)).
  • The tires will get flat spots on them from sitting under load for extended periods.
  • Brake system gets water as mentioned above and can rust up. The brake discs will also grow a layer of rust which is otherwise scrubbed off during regular operation.
  • Engine oil can take on water if the car sits for a very long time so it's best to change this if you suspect anything.
  • Fuel tanks will take on some water if there isn't a perfect seal (on 20+ year old cars good sealing is rarely the case).

The above list is actually very brief; there are loads of issues that crop up if you don't drive the car regularly. Questions are welcome and I will try to answer them to the best of my ability.

If for some reason you can't drive your car (as is the present case with my 83), then take measures to keep it dry in and out, keep the fuel stabilized and full if possible, fog the engine intake with fogging oil, etc, etc. My jag is currently under a tarp (not the best thing for the paintwork, but at the very least it keeps water from running all over the car and into the slightly leaky windscreen seals. A 13.8V power supply I built is sitting in there plugged into the cigarette lighter socket to keep the electrical system energized and the battery floated. There's also a small heater set on low which keeps it above 10°C to help drive out moisture. So far it seems to be doing fairly well.

If you can drive the car, do your best to drive it for longer rather than shorter drives. The short drives cause a build up of gunk in the engine since it doesn't necessarily get to run at full temperature for very long. Long highway drives are a treat for the Jag and its owner no matter what the occasion. This kind of driving, if it's all you ever do with the car, will keep it in better condition than any other kind of driving and especially better than sitting. The long hauls get the engine well-lubricated and bake out all the water from everything. The brake system gets nice and warm, it gets operated, and the water bakes out of it. The bearings in the drivetrain get warmed up and lubricated, etc. It all gets better with these nice long drives!

So fire that beast up when you have a moment and go for a drive, if even just for the hell of it!


It’s all about the timing

I know I said I wouldn't post too much of a technical nature but I can't help it. My most recent work on the Jaguar involves ignition timing; a very important aspect of engine tuning for any car (unless it's diesel). I've always wanted to see what I can make the XK engine do; it's a very old design (1940s) and obviously not up to modern standards, but in its time it was one of the very best.

There are all kinds of things you can do to an engine to get more power output, or more economy, or whatever it is you're trying to achieve. An XK motor apparently responds well to porting and polishing, variations in valve timing, etc. The XK also burns fuel slowly due to its hemispherical combustion chambers and thus requires quite a bit of spark advance in order to get much output or efficiency.

The big issue with advancing timing is detonation; combustion temperature rises and so does pressure. If these get too high, the fuel will undergo compression ignition due to the temperature and pressure and cause a detonation. Fuel/air charge in engines is meant to burn smoothly from the point of ignition outward; this causes the pressure to rise gradually and makes the work done on the piston more effective. There is such a thing as too slow of course, but too fast is dangerous. If the entire charge ignites at once the pressure will rise with extreme speed, almost instantly. This is equivalent to slamming on the pistons with a big hammer. Add a lot of heat to the equation and you'll melt big holes right through them.

Enter octane: The octane rating of a fuel refers to its detonation resistance. This rating doesn't actually say how much octane is in the fuel, but states the detonation resistance relative to the same amount of octane. The detonation resistance is caused by making the fuel less likely to undergo autoignition (compression ignition) and thus you can operate the engine at higher combustion temperature/pressure without detonation. Higher octane fuel is more expensive but it serves an extremely useful purpose if you're trying to get a lot of gusto out of a given engine configuration. Check out the Wikipedia article on Octane Rating.

A stock XJ6 series III is set up with somewhere between 8° and 17° static timing advance depending on the year. The distributor advance curves are different to accommodate. This makes it tricky to give useful tuning information in a general sense; it must be applied differently for the different distributors.

My XJ6 was one with 17° static advance and that means that the distributor is designed to add less advance than the 8° ones are. What this means is that I can get away with a bit more static advance without pushing the dynamic limits too far.

I decided upon running 91 octane fuel (average of MON and RON numbers for Canada, it would be a higher number in Europe being that they use RON). The reason for my choice is that it has the best price break before moving to 97 octane, though I may try 97 and see how much advantage I can get out of it.

By advancing the timing a small benefit in thermal efficiency is had in the engine since more of the heat produced is doing useful work on the piston instead of going out the exhaust. There's a point at which you can maximize fuel cost with power output and that's what I'm attempting to do. I've found with 91 octane and timing advanced to around 20° before top dead center gives a reasonable improvement of efficiency and some more power. It's not a ton more power, but is definitely noticeable. A bit more advance gives a bit more output but I'm staying on the careful side as I don't like the idea of running my engine with detonation occurring.

Detonation will only occur under heavy load when the cylinders are being filled maximally (fairly wide throttle openings). If the engine is running at full load and very low RPM then this can be achieved without opening the throttle all the way since the engine simply doesn't try to suck in anymore air than the throttle is letting by as it would if it were spinning faster.

Making any of these tuning adjustments is risky and you should ask someone with lots of experience if you wish to try it out and aren't sure what you're doing. You can destroy your engine by running too much advance! You have to listen especially for detonation under heavy load such as when climbing a hill quickly. It sounds like a hammer clunking against a hollow engine block. The sound is very memorable but you won't know what you're listening for unless you've definitely heard it before. The best thing to do if you hear it is back off the throttle and don't load the engine so hard until you've retarded the timing somewhat.

I will post later with updates as I go along seeing where the sweet spots are for power, economy, and both. I will post dyno results if I can get some. As an example of my engine's state of tune; it has 275,000km on the clock and will burn some rubber from a standstill on dry pavement. Most series III XJ6 cars don't make that much torque from a standstill. (A manual transmission would make it easier to do a burnout, mine is still an auto.)


When your spirit is crushed…

All of you who own classic Jags must know the feeling of hopelessness that can settle upon you when something goes wrong with your pride and joy; all that hard work you put in and it just didn't turn out for you. I've been there, my transmission failed, I rebuilt it, it failed again... My XK motor's head studs broke and I tread that fearsome no-man's land of drilling them out and machining the block to accept heli-coils. These are no small works to even the most experienced owner and can all but make you want to give up. If there's anything I could say to convince you to press on for your Jag it still wouldn't hit home like this video.

Nothing else reminds me to keep on keeping on so much as watching that video the one time I've watched it. I don't know if I could watch it again...