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Valve clearances are the small gaps between the tops of the valve stems and the part of the mechanism which presses on them to open the valves.engine valve oil seals sophisticated technology.
Check the clearances at regular intervals as specified in the car service schedule, and adjust if necessary. Reset the clearances whenever the cylinder head has been removed.
The job is commonly called adjusting the tappets.
A few cars have hydraulic tappets, which are self adjusting and do not need checking.
Before starting, make sure you know the type of valve mechanism commonly called valve gear – fitted to your engine, and the relative valve clearances. The car handbook should tell you the clearances – if not, consult a dealer or the car service manual.engine valve oil seals sophisticated technology.
The valve gear fitted to your engine will be either pushrod (OHV) or overhead camshaft (OHC) (See The engine – how the valves open and close). There are two types of OHC valve gear direct acting and indirect acting.
The tappets on an OHC engine are usually adjusted by placing shims of a predetermined size under them.
That is a job best left to a garage which has a micrometer for measuring shims, and a wide selection of them. But you can check the clearances yourself, and decide whether they need adjusting.
You must know the firing order of the engine, which cylinder is No. 1, which are inlet and exhaust valves and which rockers or cams operate them. Make a plan of all this information on paper.
Measure the gap between the rocker pad and the valve stem; the feeler blade should slide in to a close fit. If it will not go in or if it goes in with room for movement, adjust the gap. Leave the feeler gauge in place whilst you adjust. Use a screwdriver to prevent a slotted adjusting screw from turning while you tighten the locknut, then re-check the gap.
Measure the gap between the rocker pad and the valve stem; the feeler blade should slide in to a close fit. If it will not go in or if it goes in with room for movement, adjust the gap.
Leave the feeler gauge in place whilst you adjust. Use a screwdriver to prevent a slotted adjusting screw from turning while you tighten the locknut, then re-check the gap.
Find the correct valve clearances for inlet and exhaust valves, and whether they should be adjusted with the engine hot or cold.ring seal.
`Hot’ means that the engine must be warmed to normal working temperature, then switched off – and you must work quickly before the engine cools.
`Cold’ means absolutely cold: the engine must not have run for at least six hours – check in the car handbook.car seal.
To speed up the job on most pushrod and some types of indirect-acting OHC engines there is a sequence by which you can check more than one valve at a time. But the valves of overhead-cam engines usually have to be checked singly.engine valve oil seals sophisticated technology.
Remove the air cleaner if it overhangs the rocker cover (See Air filter change).
Tag and number the ignition leads to avoid confusion when replacing them, then remove them from the plugs, pulling the plug caps, not the leads. If the leadre clipped down and in the way, unclip them.
Note the position of any pipes, control cables and other items fastened to the rocker cover, unfasten them and move them aside.
Remove all the plugs with a plug spanner. With the plugs out, there is no compression in the cylinders, so you can turn the engine easily.
Remove the screws or bolts holding the rocker or cam cover to the cylinder head. Carefully lift the cover together with its gasket. Put the cover in a clean place, upside-down on newspaper to catch oil drips. Always fit a new gasket to the rocker or camshaft cover before refitting .engine valve oil seals sophisticated technology.