Setting Valve Clearances

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Correct adjustment of the valve clearances is vitally important for the correct running of any engine.  Too tight and valves will overheat and may even burn out at the seat, leading to low or no compression.  Too slack and increased wear will occur in all valve train parts and the engine will be decidedly noisy.

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Basic Procedure for Any Engine

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There are several methods of setting valve (tappet) clearances, some more complicated and more confusing than others.  This method is simple, logical and will work on any 4 stroke petrol engine.

 

a. Remove the spark plugs and turn the engine over until number 1 piston is at TDC with the rotor arm

    aligned with number one spark plug lead position on the distributor (or magneto). A trick is to plug the

    spark plug hole with a bottle cork and it will pop out confirming the piston is on its compression stroke.

    (Remember, the camshaft and distributor rotate at half crankshaft speed).

c. Number 1 piston will now be at the top of its compression stroke with both inlet and exhaust valves fully

    closed.   

d. Adjust the inlet and exhaust valve clearances to the manufacturer's settings. 

e. Now turn the engine over until the next piston in the firing order is at TDC, the valves will be closed and

    in position to be set.  (A brazing wire through the spark plug hole will enable you to determine TDC).

f.  Simply repeat this process for each cylinder following the firing order.  Double check in each case that the

    rotor arm is pointing towards the spark plug lead of the cylinder you are setting.  Two turns of the engine

    and all the valve clearances will be set.

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Rolls-Royce Silver Ghost - Technical Details

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The engine is 6 cylinder, side valve design with 2 valves per cylinder.

 

The cylinder firing order of the engine is...  1, 4, 2, 6, 3, 5.  

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Valve Clearances:  Back in the day = 0.002".   Today's higher speed touring = 0.004".

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The engine is a 4 stroke (ie) Intake (suck), Compression (squeeze), Power (bang), Exhaust (blow). 

This means that in order for a single piston to go through a complete power cycle the crankshaft has to complete two full rotations (two rotations of the crankshaft for every one rotation of the camshaft and distributor).

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Tools Required

 

You will require two 5/16"W open ended spanners, one 3/16"W open ended spanner and a 3/16"W locking spanner (see photo above) a large screw driver or pry-bar, spark plug key and 0.004" feeler gauge.  It is advisable to remove the exhaust manifold down-pipes, therefore you will also need the correct c-spanner. 

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Procedure for Silver Ghost 

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Sir Henry Royce decided that in order to maintain the Ghost engine as whisper quite as possible valve clearances should be set to 0.002".  A hundred years ago road surfaces were poor, average road and engine speeds were decidedly lower than today, where we now tour on asphalt roads at speeds up to 60 mph. The general consensus is to err on the more generous side and set the valve clearances to 0.004".

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Once correctly set, the valve clearances will require checking after 1,000 miles but may not require adjustment for some 5,000 miles.

 

1. Remove the exhaust manifold down pipes. 

2. Remove the spark plug from over the top of each cylinder.

3. Remove the distributor cap and note the position of the number 1 spark plug lead.

4. Using a large screwdriver or pry-bar, turn the engine over at the flywheel, counter-clockwise (looking

    forward towards the radiator) until the top Dead Centre mark on the flywheel lines up with the pointer at 12

    o'clock, with the rotor arm aligning with the number one spark plug lead position on the distributor.

5. Should the rotor arm be pointing towards number 6 spark plug lead, turn the engine over one full

    revolution.  Remember, the camshaft and distributor rotate at half crankshaft speed.

6. Number 1 piston will now be at the top of its stroke with both inlet and exhaust valves fully closed.   

7. Lock the tappets together using the 3/16"W locking spanner and loosen the 5/16"W locking nuts which

    will enable you to adjust the clearance (0.004") between the valve stem and the tappet. 

8. Now turn the flywheel through one third of a revolution, this will bring the next piston in the firing order

    (number 4) up to the top of its stroke with both valves closed and ready to be set (see Note below).

9.  Simply repeat this process for each cylinder following the firing order.  Double check in each case that the

     rotor arm is pointing towards the spark plug lead of the cylinder you are setting.

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Note:  There are 6 nuts on the flywheel (see photo 3 above). It is relatively easy to rotate the flywheel through 1/3 of a revolution using a large screwdriver or pry-bar half way between every other of the 6 nuts evenly spaced around the flywheel.  A position on the pointer, half way between these nuts will correspond to one of the pistons being at the top of its stroke and so making the task of moving onto the next cylinder in the firing order easy to locate.  Remember to double check the position of the rotor arm in each case.

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Last but not least - Check the cylinder compressions with an accurate compression gauge.