Hi Folks,  I decide to take on the task of setting the valve clearances on my '68 Jag this week. In the hopes that this might help others facing the same project I thought I would describe the process as it applies to my '68 4.2 L XK engine.

Tools: Torque wrench, 18 mm socket and deep 7/16th and 1/2" sockets, the jaguar cam setting tool and most important- measuring calipers or a micrometer.

Time: Figure on at least a couple of days if you haven't done this task before

Parts: Cam cover gasket, shims (can mix and match or sand off old ones as I did) Sealant/gasket dressing and new camshaft sprocket locking plates

Procedure:  

1) Remove cam covers, measure the clearances carefully and record, I recommend making a diagram, my car has later XJ6 cams with four bolts and 12/1000 intake and 13/1000ths  exhaust. You might also want to remove the breather cover on the front of the head at this time as well because you will likely need to adjust the chain tension during this process as well.

2) Remove cam/sprocket bolts, extreme caution here, I packed a rag around the openings to keep from losing a bolt in the timing case.  On mine there are four bolts so I started on the 'underside' ie notch down, removed the two bolts then rotated the engine around and placed the cam alignment tool in position in the respective notch and removed the remaining last two bolts. The engine CANNOT be turned from this point forwards till the cam is replaced!

3) Remove the camshaft bearing caps, I started in the center and turned a 1/4 turn on each one working out sequentially as one would do with head bolts, till they are loose.  The front of the cam will be pushing out with quite a bit of pressure so be prepared .  Once the nuts and cam bearing caps are removed then take the cam out and set upright in a safe location.

4) Now you need to pull out a tappet cup, I started on #1 (in Jags it's next to the firewall), use a magnet and the cup should come right on out. The shim lives inside here and will sometimes come out with the cap so don't loose it.  Now wipe it off and measure it's thickness and record.  Repeat with the rest and record.  If you are more organized than I am you can set them aside, I was afraid I would mix them up so I would put them back in the engine when I wasn't working on them.

5) Shims are available in sizes from .075" to .120" and gernerally cost about $4.00 apiece.  At this point you have measured all of the shims and now need to calculate the size of the shim you will need. Example: # 6 Intake on my engine had a clearance of 9/1000 and should be 12/1000, the shim was .081' thick so I needed a shim .078 thick to give me the additional clearance.  I spent half a day sanding mine down on a glass plate, it's a lot easier to just measure and order new ones but I didn't want to wait a week for them to come in the mail.

6) Now you have all the correct thickness shims in place and the tappet cups are back in place so it's time to replace the cam.  This is slightly tricky and I needed an extra set of hands.  If the cam 'snaps' out of position you could be in a world of hurt, a valve could hit and bend it's counter part (intake or exhaust depending on which one your working on) or hit the top of a piston.  To avoid this possibility I used the cam tool to position the camshaft, it won't set down in completely because one lobe will be compressing a valve. Place the camshaft bearing cap in place and position the washers and nuts on the studs.  I threaded the studs near the firewall 3-4 threads and then pushed the camshaft down with one hand holding the camshaft tool and had my helper thread the nuts on the front studs.  Once these were started I carefully tightened down the nuts keeping the camshaft adjusting tool in it's notch and guided the cam down by sequentially tightening the nuts until they were tight at 15 ft/lbs.

7) Now we need to replace the camshaft sprocket to cam bolts, again stuff the opening with a rag then replace the locking plate and bolts, if you have a 4 bolt pattern you will need to rotate the cam to gain access to the two on the other side (don't let the rag get caught in the chain). I haven't been able to find a torque setting in the manual but I set mine to 20 ft/lbs which should be adequate with the locking plates.

8) Repeat for the other side , adjust the chain tension,  recheck the clearances, replace the cam covers and your done!

9)  This is a very good time to check the upper timing chain tension, I used a pair of needle nose pliers to rotate the eccentric cam that tightens the chain. The first thing you have to do is loosen the nut with the 18 mm socket (you were wondering when we used this?). Then push in the 'pin' at the top and rotate the eccentric cam adjuster with the needle nose pliers till the chain feels snug.  This is the reason that this is a good time to do it as with the cam covers off you can feel the tension under the cam sprocket on either side.

CAUTIONS:

The engine has to be on TDC for #6 (the lobes on the intake and exhaust will be pointed out like floppy rabbit ears) and cam tool in place

Once the cam is loosened from the sprocket do NOT turn the engine

Exercise caution and don't drop a bolt down into the timing case-this will ruin your day-guaranteed 

Don't let the cam 'snap" , this too will ruin your day!

Hope you find this helpful, please feel free to contact me for questions or if there is something that's not clear.

Cheers,

Lynn G.

January 2009

PS: Here is a link to a web site that does a better job of describing the process <http://www.jag-lovers.org/saloons/faq/valve.html> you will have to cut and paste into your browser as I can't recall how Rod showed me how to do it.