Jaguar XK Engine Valve AdjustmentPaul Saltwick
These notes are only intended to supplement your repair manual. A valve clearance adjustment on an XK engine is time consuming and hard on your back, since you must remove the camshafts each time you change shims, and it sometimes takes several attempts to arrive at the best settings. The job is much easier with the head on a bench and it is worth putting the job off if any major engine work is considered.
If the clearances are too tight (small), you run the risk of burning valves, if they are too wide (large), noise is the primary problem. A certain amount of valve noise is inevitable in a mechanical system, especially when cold.
Some of the risks of doing this procedure are; bending valves by striking the opposite valve or piston, bending or breaking camshafts, and burning valves that have been tightened too much.
XK engines primarily had two different valve clearance settings, 0.004 IN-0.006 EX for pre-XJ-6 engines and 0.012-0.014 (Both) for post 1968-69 engines, so check your manual. If your engine is fitted with later cams, high performance cams, or a later head, you may need to use the wider settings, which by the way, were designed (with the cam) to quiet the valves. Later cams can be identified by having four taped holes in the front sprocket mounting plate and no holes in the lobes for oil distribution.
Some things to remember:
Jaguar cam timing plate
Jaguar timing chain adjuster
1-1/4" or 1-15/16" wrench for crankshaft bolt
1/2" and 7/16" sockets and open end wrenches
3/16" Allen wrench or driver
Tach drive and plug O rings
Half moon seal
Optional: Stat-o-seal washers
Clean crankshaft damper and mark the TDC, 5 and 10-degree BTDC lines
Mark and remove spark plug wires and spark plugs
Remove cam covers and sop up any oil
Measure and record clearances by rotating the crankshaft until the cam lobe is opposite to the cam follower (pointing up toward the center of cam bearing cap) and sliding the feeler gauge between the heel of the cam and the cam follower. The feeler gauge should feel snug and sometimes you have to work hard to slide it in place.
If any of the valves need adjustment:
Rotate the crankshaft to TDC compression for #6 cylinder (front). Since the cam rotates at half crank speed you may have to go around twice. The timing notches in the cams will be pointing up along the cam centerline when you have arrived at the proper point. Note that the cam lobes for #6, intake and exhaust, will be pointing in opposite directions (toward the outside). This may be helpful if you ever mix up which camshaft is which. Check the cam timing with the plate placed in the notch of each cam.
Remove the front breather. Remove the tach generator. I have found that the best tool for this is a small 1 inch long 3/16" socket head (allen) driver bit which you can turn with a 1/4" open end wrench , but a ratcheting bit driver may be best. I have not had much success with L shaped allen wrenches. Remove the sealing plate on the exhaust side.
Set the crankshaft at 20 degrees BTDC so that all the valves can be fully opened without hitting any pistons (timing slots near center). You can approximate this by setting the crankshaft double the distance from the TDC mark to the 10-degree BTDC mark on the damper.
Loosen the timing chain by loosening the lock nut (not too much, it can fall down in the sump), pressing the plunger and rotating the plate clockwise with the timing tool. Cut and remove the lock wire on the camshaft retaining bolts and remove the bolts. This can be tricky and you might want to put a rag in the timing chest to prevent anything from falling down. Pull the sprockets forward away from the cams.
Remove both cams by alternately loosening the cam bearing nuts a few turns at a time (note whether the caps are numbered or marked, if not, mark them to ensure getting them back in their original places). Pay attention to which lobes are pushing open valves and try to relieve the pressure evenly to avoid stressing the camshaft.
Use a magnet to remove each cam follower and shim. Inspect each cam follower and tappet guide for wear marks and corrosion. If a tappet guide is loose, it may have hit the cam lobe and marks should be evident. This apparently is a problem in later engines, mostly on the exhaust side, and there are several methods to anchor the tappet guide.
Do one valve at a time and record the shim thickness on a chart. Add or subtract to the shim thickness the amount needed to bring the clearance into spec. and put the required shim back in place completely dry. There are several theories on re-using old shims. Some say don't do it, others say OK if there are no indents, and still others say flip 'em over. I have reused them with no apparent problems.
If any of the clearances cannot be brought into specification with the minimum shim (0.085 ) recommended by Jaguar, the proper solution is to remove the head and fit new valve seats or grind down the valve stems .010-.015. If you use shims of less than 0.085, the shim may sit so low in the spring retainer that the follower will open the valve by pressing on the spring retainer (bad idea).
If you are getting your head rebuilt, make sure that the machinist does not grind down the valve seats too much or you will not be able to get the proper valve clearances. This is especially true for heads that have previously been reconditioned. This is one time when it pays to have one individual replace the valve guides, cut the seats and set up the cams. This way if the seats are cut too much, he will have to disassemble the head and grind down the stems until the proper clearance can be obtained. You don't want to first realize this after you have paid and assembled the head. If you go this route, be sure to discuss the minimum shim thickness to avoid the possibility of someone grinding down the shims. Another alternative is to fit undersize followers which will give you more clearance to use thicker shims and avoid taking your head off (a good thing).
After you have finished one side, re-install the cam by alternately tightening the cam bearing caps. Torque the cam bearing caps to spec. (9 or 15 ft/lbs.). Rotate the cam and remeasure the clearances. If everything is all right, remove the cam again and move onto the other side.
While you have the cams out check the condition of the cam bearings. You will probably notice that most of the wear is on the top bearing shell. I have heard it is acceptable to swap upper and lower bearing shells, but I have never done it since new ones aren't too expensive.
After both sides are done, reassemble both cams, with their timing slots pointing up, after lubricating the shims and followers. I like Moly paste for this especially if the cam or followers are new. Torque the cam bearing caps. Reset the crankshaft to TDC and reset the cams with the timing plate. Reattach the sprockets and safety wire the bolts. Adjust the cam chain tension according to the manual, it should not be "dead tight" and some slack should be present. This can be tricky, so you may want to rotate the engine back and forth and check it again. Recheck the valve timing with the timing plate.
Sealing things up:
Several times I have found that, when I thought an oil leak was coming from the crankshaft or transmission, it was really coming from the cam covers, rear seals or the oil line. The covers are long and the gasket is not held in place by studs and people have a tendency to keep tightening the nuts to solve leaks. The rear of the head is a mess of oil lines, coppers washers, O rings , silly seals, and through bolts, all of which can cause leaks down the bellhousing. It pays to get all of this set up properly.
I have used Hylomar, Permatex and Permatex "Right stuff" and have found "Right stuff" does the best job, but I'm sure you can succeed with many different products. "Right stuff" is expensive, messy and slippery, so you have to be careful you don't squeeze out the gasket when tightening down the cam covers.
Another product I like are "Stat-o-seal" washers. They are aluminum crush washers with an imbedded O ring and placing one under the copper cam cover washers and on the rear through bolts will guarantee against leaks. They are available from most discount race supply shops.
An obvious (not to me) thing to check is the height of the cam bearing studs. Since the cam cover nuts are acorn nuts and have a fixed range, if the stud protrudes too far above the cam cover you will not get an effective seal on the gasket or the stud hole. Measure them or try to move the washer side to side after you've tightened the nut. If the stud is too high, you can add another washer.
All that remains is to hook everything up and start the engine. If you have a new cam or tappets follow the recommended break-in procedure, usually 2000 rpm and no idling for the first 20 minutes.
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