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Checking valve guides
Check valve guides for wear by first refitting a valve into its respective guide, then raising the valve slightly off its seat.oil seals  durable in use.
Try moving the valve head from side to side. If the movement at the valve head is more than 0.007 in. (0.2 mm), the valve guide or the valve stem may be excessively worn – check the manufacturer’s specifications, given in a service manual, or consult your local dealer.
Hold a block of wood over the cylinders to prevent the liners rising.
If there is too much movement, repeat the test using a new valve. If this has less movement, the old valve stem is worn and the valve must be replaced. If there is still too much movement, the wear is in the guide and the cylinder head should be taken to an engineering shop for the replacement of all the guides.oil seals  durable in use.
If the guides are an integral part of the cylinder head, they can be reamed – opened out – to a larger size to take new valves with oversize valve stems. This work should also be entrusted to an engineering shop.car seal.
Grinding and refitting the valves
Generally valves should be ground, or ‘lapped’, into their respective seats to ensure a gas-tight seal. Grind-in each valve (including new valves) by hand, using a valve-grinding tool and valve-grinding paste.
On some modern cars the valve faces have a thin coating which must not be removed. When fitting coated valves, use an old valve to grind the valve seat.
Smear clean engine oil on the valve stem, and attach the valve head to the sucker on the end of the grinding tool.
Smear a thin film of grinding paste round the chamfered edge of the valve head and insert the valve fully into its guide.
Rotate the grinding tool back and forth between the palms of the hands, pressing the tool and valve into its seat at the same time.
After a minute of continuous grinding, raise the valve off its seat, revolve it about 45 degrees, then continue the grinding process for another minute.
Repeat the grinding procedure, altering the position of the valve periodically until both the valve-head flange and the valve seat have an even, matt-grey appearance, which indicates that the valve and seat are making good contact all the way round.
If slight pitting remains on the seat, use a coarser grinding paste, followed by fine paste.oil seals  durable in use.
Check the valve stem and guide by trying to move the valve from side to side in the guide.bearing seal.
Check the valve stem and guide by trying to move the valve from side to side in the guide.
When all the valves have been ground-in, remove them and place each in its order of removal.
Wash the cylinder head, combustion chambers and valve ports thoroughly with paraffin, to remove all traces of grinding paste.
Dry the head with compressed air from a tyre foot pump, and blow through all oilways and bolt holes.
Clean all traces of grinding paste from the valves, remembering to keep them in their removal order.
Smear each valve stem with clean engine oil and refit the valves to their respective positions in the head.
If there are oil seals, fit new ones over the valve stems, taking care to avoid damaging the seal lips. Always fit new valve springs.
Place the new valve spring and spring cap in position over the valve stem, noting that the close-coiled end of the spring is usually fitted next to the head.
Compress the valve spring with the compressor tool until the two split, tapered collets can be slipped into position between the spring cap and the valve stem.
Slowly release the compressor tool until both collets are locking the spring cap and valve stem together.silicon seal.
Remove the compressor tool and repeat the valve installation procedure on the remaining valves, in the order in which you removed them.oil seals  durable in use.