Jaguar Repair: valves adjusting

Question
how do you adjust the valves on a 4.2 litre xj6 jaguar engine one valve clicking 1987.

regards,
richard

Answer
Hi Richard,

First with a stethoscope or a wood handle screwdriver up against your ear find the area where the noise is or just which side it is, intake or exhaust. Then remove the cam cover. Rotate the engine and check the valve clearance on all the valves and write them down.

Then rotate the engine until both notches in the front cam flanges at the front cam bearing cap are pointing directly away from the cam cover surfaces.

Note that there are four bolts holding the cam sprocket to the cam flange but only two are accessable. DO NOT UNDUE THE TWO THAT ARE ACCESSABLE !! Either mark the two that are accessable or note which ones they are and rotate the engine crank 360 degrees so that the two notches are facing inward and down. Now the other two bolts are accessable. With a punch or suitable tool unlock the lock tabs on the bolt heads and then stuff a shop rag down into the chain area so that it is impossible to drop one of the bolts down into the cam chain area. DO NOT REMOVE THE WIRE CLIP INSIDE THE EDGE OF THE CAM SPROCKETS !!!!

Now remover the two bolts accessable and their lock tab. Now you can remove the shop rag and rotate the engine crank 360 degrees again which will return the notches in the cam flange to point out 90 degrees from the cam cover surface. Set the crank shaft pulley at the TDC mark.
Don't forget to stuff the shop rag back into the chain area again !!! Then you can remove the other two bolts and lock tab. Now with a pry bar of some kind pry the cam sprocket off of the flange.

Now look at all the cam lobes and note which are Pointed toward their valves. The cam bearing caps next to these valves MUST be removed LAST. Now remove the other cam bearing caps but keep them in order as they MUST NOT be mixed up. (look closely at the edge of each cam bearing cap and you will see a number and the same number stamped into the head next to it. (Also be careful to retreve any dowel guides that are loose on each stud.#

Then remove the cam bearing caps next to the valves that are depressed but alternater a few turns of each nut so as to allow the cam to raise evenly not one end first. Often when you get it almost all the way the cam may flip over, this is normal.

Now you can lift the cam out but treat it with care as it is hardened and fragil. If dropped on a concrete floor it most likely will break into several pieces. Also be careful not to get any cam bearing shells mixed up if any stick to the cam and come out too.

Now lift each lifter cup out of the head being very careful not to gete them mixed up and be very careful to get each valve adjustment pad and keep it with it's valve and lifter cup.

Now you need a accurate caliper or a micrometer to measure the thickness of each valve adjustment pad. Now to get the correct valve clearance you need to change the pad thickness to get the correct clearance. #.012" to .014")  

For example when you checked clearance at first and found a clearance of .018" on a valve and that valve pad measured .090" Then you must replace that pad with a .095" pad. Thus bringing down the clearance from .018" to .013" as a target figure. You should check and adjust all the valves on that cam as some can be off but not making noise YET. A valve can get tight too due to valve seat recession. These too are very dangerous because they will cause a valve to burn.

It is a good idea to do both intake and exhaust at the same time. Note that some valve pads will get a indentation where the valve stem wares and you can not turn it over unless you reassemble the cams again and measure the valve clearance again in this position. Also if you have some that have the indentation you need to measure that pad in the center with a mic not a caliper and not the unworn part of the pad as that will cause your math to be wrong.

After the cam or cams are back in place it may take a pry bar to get the cam sprocket up onto the cam flange again. If the upper chain tensioner is loose the sprocket will go back on easily so you should check the tension and adjust it (a whole different story) If it is too difficult to get back on then the upper chain tensioner may have been too tight and again it may need to be adjusted. Some jaguar mechanics loosen the tensioner when doing any valve adjustment work but they have the special tools necessary to adjust the tensioner. Let me know if you want to adjust the tensioner and I will go through the procedure.

If you know a shop that does Jag work they may have an assortment of pads and might loan them to you to do the job thus you won't have to tear it down and then order the sizes you need from a Jag parts supplier. Don't attempt to use any kind of shims to take up the clearance.

One other point is the exhaust valve side should have a "Stake Down" kit added to prevent the lifter bores from migrating up from the head. These are two bolt plates that hold the lifter bores seated. If your engine does not have them on the exhaust side you should get a set and install them. They are not expensive and are needed on all XK and XJ engines. They are available from Jaguar and from most of the aftermarket Jag parts suppliers.

Howard