The valve clearance is checked between the tip of the valve stem and the rocker pad, with the engine hot or cold as recommended, and with the valve fully closed.

As the camshaft is out of sight inside the block, you must calculate when the cam lobe is pointing directly away from the tappet and the tappet is resting on the cam heel. This is done by turning the crankshaft until the valve to be adjusted is fully open, and then turning it again one complete revolution.

This will rotate the camshaft half a turn, putting the tappet on the heel of the cam lobe. It helps to put a chalk mark on the crankshaft pulley to show when it has rotated one revolution.

Step 1. Identify the inlet and exhaust valves.

2. Turn the engine, using the rule of nine or thirteen, until the valve is fully closed.

3. Insert the appropriate feeler gauge into the gap. It should slide in under moderate pressure. If it is too loose or too tight, move to Step 4.

4. Where the rocker has an adjuster on one end, loosen the look-nut, and turn the adjusting screw clockwise to reduce the clearance, or anti-clockwise to increase it. Some engines have purpose-made, stiff adjusting screws which do not have a lock-nut.

5. Some pushrod engines have the adjusting nut at the centre of the rocker, and the valve clearances are set with the engine at normal operating temperature and running. Do not use an ordinary feeler gauge for this—dealers sell long feeler strips for the pur- pose. Make sure that you have no loose clothing; it could be caught in the engine orfanbelt.

6. Run the engine at idling speed. Put a socket or box spanner on the adjusting nut. Insert the feeler blade between the moving rocker pad and valve stem. If the gap is too small, the feelerwill be difficult to fit and the engine will run unevenly when it is in position. If the blade rattles, the gap is too wide.

7. Adjust the nut until the engine runs smoothly and any feeler blade rattle disappears. If you find this difficult, stop the engine and check the gap stat- ically.