XK Engine Valve Adjustment Procedure
by Pat Harmon
Overview
The Jaguar XK engine valve setup is significantly different from that normally found in automobile engines. The key components involved are: exhaust and intake valves, overhead camshafts, tappet, tappet guide and adjusting pads. The valves are mounted in the head with their shafts protruding above. An adjusting pad (they come in various thicknesses, 0.001 inch separating, and are etched with letters from A to Z) sits on top of the valve and the tappet fits over the valve and pad. The tappet rides inside of a finely machined tappet guide which has been press-fitted into the aluminum head. The camshaft rides directly on the tappet and, as it rotates, the camshaft lobes depress and release the valve in, and out of the head. The clearance between the camshaft lobe and the tappet must be exactly to spec for the engine to run correctly. If the clearance is too wide, the valves will not open completely thus restricting the flow of fuel/air and/or exhaust gasses. If the clearance is too tight, the valves open too far and do not rest on the seat long enough to dissipate the heat. Exhaust valves can be easily burned with too tight of a clearance. The valve adjusting procedure consists of first measuring the clearances on a cold engine and recording the readings. The camshafts are then removed along with the tappets. The thicknesses of the installed adjusting pads are then measured. If the measured valve clearance is less than spec (0.004 inch intake, 0.006 inch exhaust) then a thinner pad is installed replacing the existing one. If the clearance is larger then a thicker pad is installed.
Materials/Tools Required
Leaf-type feeler gauge
Jaguar Valve Timing Gauge
New Camshaft Cover Gaskets (2)
Rear Camshaft O-Ring Seal (2)
Bolt locking wire (rebar tie-wire works well)
Silicone Gasket Sealer
Pen-type magnet
Complete set of valve adjusting pads (A-Z)
Procedure
1. Remove all camshaft cover acorn nuts and washers
2. Remove camshaft covers (putty knife/screwdriver)
3. Remove spark plugs
4. Measure current valve clearances (Intake 0.004”, exhaust 0.006”)
a. Using the remote starter button located at the rear of the starter relay, rotate the engine until one of the intake cam lobes is pointed exactly 90 degrees perpendicular to the camshaft cover gasket surface (i.e. directly away from the tappet guide).
b. Prepare a table listing each intake and exhaust valve. The #1 valve is at the rear of the engine.
c. Using a blade-type feeler gauge wiped clean from oil, carefully measure the clearance of the valve identified in 4a above. Record the measurement on the table.
d. There should also be an exhaust valve located 90 degrees from its tappet guide. Carefully measure the valve clearance and record the measurement.
e. Use the remote starter to rotate the engine until a second intake cam lobe is pointed 90 degrees from its tappet guide. Measure and record the clearance as above.
f. Continue to rotate the engine and measure clearances until the data on all valves has been recorded.
5. Remove camshafts
a. Note the camshaft chain sprockets at the front of each camshaft
b. Remove the distributor cover and locate the pin leading to the #6 spark plug wire (front of engine). Using the remote starter button rotate the engine until the rotor is pointing to the #6 wire position.
c. There are two bolts attaching the timing chain sprocket to the end of the camshafts. One should be accessible and the other not. Mark the accessible bolt head. Rotate the engine until the non-accessible bolt head is accessible.
d. Stuff a rag into the cavity below the camshaft sprocket. Remove the safety wires from the now-accessible camshaft bolt. Remove the camshaft bolts (exhaust and intake).
e. Remove the rag and again rotate the engine until the rotor is just before the #6 wire position.
f. Using a socket wrench on one of the harmonic balance wheel bolts, carefully rotate the engine (clockwise) until the timing mark is exactly zero degrees top dead center. IMPORTANT: DO NOT ROTATE THE ENGINE BACKWARDS. ONCE THE ENGINE IS SET A THE ZERO TIMING POINT IT IS NOT TO BE ROTATED UNTIL THE CAMSHAFTS HAVE BEEN REINSTALLED.
g. The remaining camshaft sprocket bolts should now be accessible. Again stuff a rag into the cavity and remove the remaining bolts.
h. With a soft mallet, tap the sprockets off the end of the camshafts.
i. Clean-off the top of each camshaft bearing cap and number them with a magic marker. Write the same number on the gasket surface. This is to insure the bearing caps will be reinstalled in the same location.
j. Begin removing the bearing cap nuts rotating each several turns at a time. The valve springs are pushing upwards on the camshafts. As the bearing cap nuts are released the camshaft will push upwards. For this reason the caps are released gradually.
k. Remove the bearing caps and store.
6. Adjust Valves
INFORMATION: There are four engine components involved with this process: Camshaft, Valve, Tappet Guide, Adjusting Pad. The Tappet guide fits over the top of each valve. Inside this guide is a ground steel adjusting pad. As the engine rotates, the camshaft tappet (lobe) contacts the tappet guide and pushes it into the engine causing the valve to open. The clearance between the lobe and the guide is adjusted by replacing the adjusting pads with ones of different thickness. REPLACING AN EXISTING PAD WITH A THICKER ONE WILL REDUCE THE EXISTING CLEARANCE.
a. With a pen-magnet remove the #1 intake tappet guide and its corresponding adjusting pad.
b. Clean the adjusting pad and carefully measure and record its thickness.
c. Note the valve clearance for this valve as previously measured and recorded. Determine the difference (in ten-thousandths of an inch) from the factory specification (0.004 inch). Note the removed adjusting pad’s thickness. If the measured valve clearance was below the factory specification then a thinner pad must be installed. If greater than the specification then a thicker pad must be installed. The thickness of the new pad will then be the old pad thickness, plus or minus, the difference in specification as above.
EXAMPLE: The measured/recorded valve clearance for intake valve number one was 0.0046. This is 0.006 greater than specification. The adjusting pad currently installed in the engine is size K (0.0950 inch). Since the gap is 0.0006 to great a thinner pad is required. The thickness of the replacement pad should be 0.0950 minus 0.0006 or 0.0944 or size J.
d. Repeat this process for all of the other valves. It’s highly recommended that only one valve be adjusted at a time to avoid the possibility of mixing them.
e. Replace the camshafts aligning them with the camshaft adjusting tool.
f. Leave the adjusting tool in place to prevent the camshaft from turning. Replace the bearing caps and slowly screw-down the cap bolts. You may have to exert pressure down on the camshaft to get some of the nuts started.
g. Torque the bearing cap nuts to 14.5 foot pounds.
h. Verify the cam adjusting tool in in-place and is touching both gasket surfaces on the head. If not, the camshaft may be turned slightly using a large pliers.
i. Tap the camshaft chain sprocket onto each camshaft.
j. Stuff a rag into the engine cavity and insert one sprocket bolt and tighten. Do this for both camshafts.
k. Remove the rag. Insert a bolt tie-wire through the bolt and twist it to reach the other bolt plus two inches. Tuck the wire against the sprocket so that it will not foul when the engine is rotated.
l. Rotate the engine until the second sprocket bolt hole is exposed. Stuff a rag into the cavity, install and tighten the bolt.
m. Feel the exposed end of the tie wire through the second bolt and secure.
n. Recheck all valve clearances.
7. Replace Camshaft Covers
a. Clean gasket surfaces on both head and camshaft covers.
b. Inspect the camshaft rear O-ring seal and replace if worn.
c. Install camshaft cover gaskets with silicone sealer.
d. Install camshaft covers with copper washers and acorn nuts.
8. Final Steps
a. Remove distributor rotor and oil the shaft center.
b. Replace the rotor and manually turn to verify mechanical advance is not stuck.
c. Replace the distributor cap.
d. Start engine and check for leaks.