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Front of the Engine

   The XJ6 Jaguar
Front of the Engine


Timing Chains

The front of the engine: Here we are into the engine itself, the timing chains. There are both an upper and a lower timing chain. These items are so inexpensive that I have a new set on the shelf ready to use if I ever need them. This will probably protect me from ever having to replace them. Murphy's law always says that the part you don't have or can't get or is most expensive is the one that will break. These are cheap and easy to get.

The first indication that you have a problem will be a noise from the front of the engine. If the tensioner becomes worn or becomes dysfunctional you will hear the chain slapping around. If it gets loose enough the valve timing will be affected such that the car does not run smoothly.


Tappet Followers

The head: One of the weak points of the 6 cyl engine is that the valve tappet followers will eventually loosen up so that they do not stay seated in the head. It is an easy fix and should be done before they start slipping around.

If the tappet follower comes loose there is a ticking noise from under the cam covers. The sound can be likened to the sound of a sewing machine. Oddly enough I have heard people say, "Its so smooth, it sounds like a sewing machine." In this case, that is not good. A loose follower can cause all kinds of damage to the engine, mostly in the head.

Many XJ6s have had the stakedown kit installed already and you can tell if yours has one by reaching your finger deep into the oil filler hole on the cam cover and if it is there you can feel it. I must admit I could not find it when I felt, but a mechanic friend of mine felt and assured me it was there. By the way, don't try this if the engine is warm.

A stakedown kit will run about $300(US) installed at 1995 prices. It is a cheap piece of insurance. If it hasn't been done, do it before you trash your engine!!!


Head Improvements

While we are on the subject of the heads, there is alot of work that can be done here to improve the performance of the XJ6, especially the series 1 and series 2 versions. By the time the series 3 came out the head had been very much improved from the MK VII head from which it evolved.

I have heard it said that you can gain 50HP just on head improvements alone.

From Julio Loza I received the following advice on removing the head when it is stuck.

"While rebuilding the cylinder head ( it was warped and leaking water to the cylinders) I found the studs frozen in place. No matter how hard I tried I could not pull the head off with the studs on. I tried soaking them in various solvents to dissolve the rust but to no avail. At the suggestion of the local Jaguar shop, I tried an impact wrench to 'loosen' the studs but this did not work. Here is what a friend suggested and worked:

1. Buy a few of nuts that fit the studs. ( I got mine at PepBoys)

2. Take two nuts and tighten them on one of the frozen studs.

3. When they are both in far enough, take two wrenches and try to undo the bottom one while tightening the top one. You are basically compressing the two nuts against one another.

4. Once they are as tight as they will get, try undoing the bottom one only. This may require a long pipe to get enough torque. If the nuts are tight enough the frozen stud should begin to turn. If the top nut begins to turn instead, tighten them more.

5. This procedure took all of the studs off and none were damaged. After a couple of uses, the nuts will begin to strip and need to be replace with new ones. This procedure will only take an hour or so and will make the removal of your cylinder head a lot easier."

I had a head stick on a 1968 420. We took all the nuts off then squirted WD40 into every nook and cranny. Then we hooked a hoist to the head as though we were going to remove the engine. We lifted the car so that the front wheels were 2" off the ground and let it hang. Every day we would squirt in more WD40. After three days the head slipped off and the car came down with a thump.

The exhaust side of the XJ6 head is just about as good as you need it to be no mater how radical you get on improving the engine. Some of the D-type heads had huge exhaust valves by comparison, but they are not necessary. There is little to be gained on the exhaust side, so spend your money on the intake side where it can use some help.

The first thing you want to do is the porting and polishing. You do this first so that the crap and dust that it creates will be washed away after the machine shop does their job. You don't want it getting into the new valve guides and other goodies you will be adding later.

Porting and polishing will make the biggest single difference on the heads of an XJ6.

You have two levels that you can aspire to in porting and polishing. The first level is to just smooth out the intake ports so that they are smooth and without lumps and casting imperfections in the walls. Finish the job with 80 to 100 grit sanding drums. This is probably all you will want to do for a strictly street machine. Enlarging the ports on a street machine just hurts the low end performance.

If you are into racing you may want to enlarge the ports to just under the size of the gasket openings. You can do this by placing a gasket against the head and marking the openings on the head. Then enlarge the ports to about 1/16" smaller than the gasket openings. Be careful though as there are water passages in the head and they are closer to the surface as you approach the valve seats and if you cut too deep you could be in big trouble. The cut is mostly at the port and should taper off quickly toward the valve seat to prevent disasters.

Polishing is probably not done on a street machine, but if you are into racing then you want to polish the ports down to a 1200 sand paper. They should be almost a mirror finish when done. This has to be done gradually from the 80 grit in the first step to the 1200.


Now we come to improvements of the head. There are several improvements that can be made by the machine shop that cost very little. First, the valve guides that stick out into the gas flow can be smoothed flush with the port wall. This will improve the gas flow immeasurably.

Having the heads "cc'd" will make the engine smoother and there may be an increase in power. You can do it yourself. Place the head on its back with the spark plugs installed and the valves installed Then make sure the mating surface where the head meets the block is level. Now fill the depressions in the head at each cylinder with light oil till it is level with the gasket surface. Use a syringe to remove the oil from each depression and measure what you take out very carefully in a graduated container. Write down the number for each cylinder. What you want to do now is to take your Dremel tool and sand away enough material from the inside of the head so that all the cavities are as large as the one that held the most oil. Do not grind on the one that was the biggest! You should remove the material evenly around each cylinder head. When they are all the same size you are done. Your head has been "cc'd." With all combustion chambers the same size the engine will run smoother.

The racing engine should have the heads glasspeened to relieve stress. You can do it on any engine and it is inexpensive.

Increased size on the intake valves can improve even a street car, and they are almost mandatory for a car that will be raced seriously. The intake valve size on a series 3 XJ6 is 1 7/8". This is a good size for street use and the valves are stock Jaguar items so are easy to get. The early XJ6 had 1 3/4" intake valves and increasing to the 1 7/8" series 3 intake valves will improve these engines. It is possible to increase the valve size to 1 15/16" without changing the size of the spark plug. If you go to a 2" intake valve you will have to change to a 10mm spark plug. You should not go to a 2" valve unless you are seriously racing the car.

Remember though that with the stock dual carburetors you will gain nothing with the big intake valves. The big intake valves require more breathing room, like 45DCOE Webers.

The best compromise for a street car is the 1 7/8" valves of the series 3 with improved carburation. In the series 3 of course, there is nothing to do as it already has this capability and the EFI to feed it.

While you are doing this valve work, plan on replacing all the valve springs. You will be putting in a hotter cam and the stock valve springs will float at 5500 RPM. There is no reason to do this much work and then scrimp on costs. The new valve springs won't cost that much. Use a stronger set of racing springs and you will then be able to use a hotter cam without valve float.

If you are racing the engine you will want to replace the stock steel valve spring retainers with the lighter weight alloy retainers. On a street head, these will do nothing for you, but at high revs, 6000 up they will make a difference.

Replace all the valve guides. You don't want to waste all this time then find that you have to replace a valve guide in the near future. The head is off, so replace the guides now. Use bronze valve guides as they lubricate the valve stems better and will last longer for that reason.

Considering the cost vs the improvement, one of the cheapest things you can do is to have the shop cut "triple angle" valve seats when they install the new valve seats and valves.

The new valve seats should be "hardened" seats so they can withstand the rigors of unleaded gasoline. Even if unleaded is not mandatory where you live now, it probably will be someday so get a head start on it now.

I recommend that you do your own valve lapping, the last step in this head restoration/improvement. The shop will not spend the necessary time to do it right and you will because you know that its your money down the drain a year from now when you have a burned valve and your compression is down.


Spark Coils

From Gregory Andrachuk I received the following advice on spark coils:

"The faulty or fault-prone coils are not he LUCAS coils, but the DUCELLIER coils made in France. My 82, in fact, has a DUCELLIER coil, which I presume is original, and it operates perfectly, with no leaking of oil. I think the failure is an oil seal failure to begin with. My coil has an internal ballast resistor, or so I assume, since there is no

resistor mounted beside it as on other cars I have seen. I believe that the DLC 102 coil used as a replacement requires an EXTERNAL resistor, but the sales reps don't seem clear about this. I think one should suspect coil trouble with sudden engine misbehavior, but replacing perfectly

good coils seems unnecessary."


First Piston and Cylinder

The first piston and cylinder. There is not alot to say here except to praise the quality of the XJ6 bottom end. The main and rod bearings are very tough and will last forever. It is a testament to their strength when you consider how many horsepower can be coaxed out of this engine without any change in the bottom end at all.

Jaguars are often asked to run with low oil supplies (they leak the stuff out) and on turning corners it is not unusual to see the oil pressure light flicker. This is not good and should be attended to, but it never seems to damage the bottom end of the engine to have these temporary losses of pressure.

You may have heard that Jaguar considered going into the manufacturer of refrigerators at the end of the second world war but they changed their mind when they couldn't figure out how to make them leak oil....8-)

Some owners will try to get more horsepower from their engines by increasing the compression ratio by using hi compression pistons. This is not really necessary and it makes it hard to run on the fuels available at the pump without causing damage to the engine. Here is where you can damage the bottom end. If your compression ratio is too high and the car "pings" you may not notice it and it will be beating your crank and bearings to death.

You can gain more at lower cost by reworking the head and changing the cams and you will do it with less possibility of causing damage to the engine.


Oil Pressure Sender

The distributor and the oil pressure sender and the oil pan. All of these have peculiarities worth mentioning.

The oil pressure sender is infamous for its inaccurate readings. This item is a very expensive sender at the dealer. After my first edition of this book hit the stands I recieved a phone call from one of the dealers listed at the back of the book telling me he could supply it for 60% of the price the Jaguar dealer was asking, so look around. Inside the housing is a wire wound resistor that has a wiper connected to it from a diaphragm that measures the pressure. The diaphragm is moved by a piston that can get stuck with crap from dirty oil. If this happens you may get a flat topped reading that hits a peak and goes no higher or it may get stuck so that there is a reading of pressure when the engine is not turning. Sometimes cleaning out the input end with a blast of pressurized air will make a difference, but usually it wont.

The wire on the wire wound resistor will wear and after many miles will either break or will begin sliding around on the form. When this happens you will get very quirky readings, sometimes high, sometimes low. If you start getting low pressure readings and the idiot light is not confirming the low pressure, this may be the problem.

If you go to the parts house and they tell you they have a pressure sender for your jag and it seems cheap, they are talking about the pressure sender for the idiot light. It is cheap, but it wont work in the gauge. You can tell the two apart as the light sender is only about 1" in diameter and 1.5" tall. The pressure sender for the gauge is about 3" in diameter and 3" tall and looks like a small tuna can fitted to a piece of pipe with an electrical connector on the other end.

This item is expensive and not readily repaired so the only alternative is to bite the bullet and get one from Jaguar or one of the suppliers in the back of this book. The one consolation is that it will probably last another 70 thousand miles.

One of these days I am going to attempt a repair on one that has had the wire break. I will report the results in this book, but I doubt that it will be economical, it will just be to see if I can do it.


Oil Pan

The oil pan is another place where things go wrong. Being of cast alloy it is soft and many a PO (Previous Owner) has tightened an oil pan plug too tight and stripped out the threads. One car I bought, the PO had used epoxy glue to glue the plug in place and then he changed oil using a pump. Of course he neglected to tell me this when I bought the car.

There are several ways to solve this problem. All have their advantages. All are relatively inexpensive and all of them work.

I have already mentioned the pump thing so I will skip it. Besides, I don't see any real advantage to that one. The next possibility is to put a helicoil into the old threads to rebuild the threads to accept the old drain plug. This works sometimes, if there is enough material around the hole to do the repair. It usually requires removing the oil pan which on an XJ6 requires removing the engine from the car.

The second method is to drill out the hole to a larger size and retread it. Again this requires removing the oil pan since you want to be able to remove any metal chips so they don't get swept into the engine oil passages.

There are rubber stoppers that expand into the threads when a bolt is tightened they are sometimes available in the parts stores. I don't like this solution since oil and rubber don't really mix and I would be suspicious of how long the rubber could handle the heat of the engine oil.

The best solution I have found is to install one of those "quick drain" plugs. The ones with either a remote trigger or with a lever on the plug that allows you to drain the oil without removing the plug. This way you can put a good grade epoxy glue on the plug when you install it to glue it in permanently and yet you can still drain the oil when the time comes. I like the remote trigger type and consider installing those even if I didn't have a problem to begin with. Its alot more pleasant to change the oil if you don't have to crawl under the car, not to mention, alot safer, since a Jag is so low you have to jack it up to change the oil.



The distributor is just a standard points and condenser type of distributor on the series 1. (the series 2 and 3 used contactless electronic ignition) It is adjusted in the normal way with a screw driver to loosen the arm and to pry the points apart or together and a feeler gauge to measure the gap.

It needs to be lubricated on the pivot post, through the base plate opening at the cam and on the center screw with a dab of engine oil. On the cam it should be lubricated with grease or Vaseline.

There is a vacuum advance diaphragm on the side. The most common failure of this part is the rubber vacuum hose that connects to the advance diaphragm. The rubber deteriorates with age and starts to leak so that there is no advance as the engine reaches cruise speed. This can cause overheating and loss of economy by running the engine in a constantly retarded condition. If the hose is OK you can check the advance by putting the end of the hose in your mouth and sucking. This should cause the distributor points plate to rotate slightly as you watch it with the distributor cap removed. If it doesn't rotate and the hose is good then there is a bad diaphragm in the advance mechanism and it needs to be replaced.

The coarse timing is set in the usual way by first removing the #6 (the front cylinder) spark plug and turning the engine by hand until the compression stroke can be detected by the pressure escaping around your thumb as it is held over the spark plug hole. Now continue rotating the engine in the same direction until the appropriate timing mark is in alignment with the timing cover pointer. The correct direction to rotate the engine can be easily determined by looking at the fan blades. The engine rotates such as to make the fan suck air through the radiator, i.e. the fan rotates so that the leading edge of the blades are the edge to the front of the car toward the radiator. Now set the vernier screw to the center of its position. Then loosen the distributor clamp so that the distributor can be turned stiffly. Set the distributor timing as close as you can get it while using a light across the points to detect the opening of the points. You want the points to just open. Clamp the distributor in this position. The car should now run well enough that you can continue with the fine timing.

The fine timing adjustment is a knurled nut on the opposite side of the distributor from the advance diaphragm. To adjust the fine timing a timing light (strobe) is held on the crankshaft damper timing marks and while watching the alignment of the marks with the timing cover pointer the knob can be adjusted to fine tune the spark timing.



On to the next part


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