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Removing and grinding valves What you'll need

  Wire Brush 

  Rag 

  Newspaper 

  Spanners 

  Emery Cloth 

  Wood Block 

  Electric Drill 

  Scraper 

  Valve-spring compressor 

  Paraffin 

 

Foot pump   Valve-grinding tool 

  Grinding paste 

Good engine performance depends on valvecondition. Worn guides or stems and burned orbadly seated valves allow gas to escape undercompression, resulting in poor starting and loss ofpower.

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Valve springs, too, can affect engine performance.Over a period of time they weaken, causing the valvesto `bounce' on their seats as they close.

Removing the valves

Support the cylinder-head assembly firmly on a suitablebench or work surface. See that there is sufficientspace to store parts as they are removed, andcardboard boxes and clean newspaper available tokeep them clean and safe.

Undo the nuts or bolts securing the inlet manifold to theside of the cylinder head; remove it, completewith carburettor if possible.

On some engines, the carburettor is unbolted andremoved before you can gain access to the manifoldnuts or bolts (See Exhaust manifold gasket

replacement).Put the manifold/carburettor assembly in a clean, safeplace preferably on a sheet of newspaper.

Similarly, remove the exhaust manifold from the side ofthe head and place it with the inlet manifold.

On some engines, the inlet and exhaust manifolds are

fitted and removed as one unit.Undo the nuts or bolts securing the thermostat housingto the cylinder head. Ease off the cover and lift out thethermostat.

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in their order of removal on a numbered sheet of cleanpaper, or push them into a piece of cardboard.

Alternatively, use the old cylinder-head gasket to•store

the valves in their correct sequence.

Each valve must be refitted in its original position onreassembly, as individual valves, valve guides andvalve seats wear in different ways.

Removing carbon

Remove all carbon deposits from the cylinder-headcombustion chambers and valve ports, using a suitablescraper, such as a blunt screwdriver, and a wire brush.

Take great care to avoid scoring the surface of thevalve seats or the machined face of the head,particularly on an aluminium-alloy head.

Clean the machined cylinder-head face to remove anyremains of the old headto store— use the smooth sideof a hacksaw blade, or a paint scraper.

Again, take care not to scratch or damage the face.

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Scrape until the face is smooth and flat. Modem headgaskets have a resin-coated finish which sticks thegasket to the surface and is often difficult to remove.Make sure you remove all of it.

Clean the carbon from each valve in tum. Grip thevalve stem in the chuck of a stand-mounted electric drill— or vice-mounted if necessary. Turn at slow speed, ifpossible, and scrape off the deposits carefully with ascrewdriver.

The valve head can be smoothed using very fine emery

cloth. Remember to keep the valves in their order ofremoval.

Inspect the face and edge of each valve, looking forgrooves, pits and for other signs of damage. If thevalves are burnt, bent or damaged, renew them.

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Check the valve seats in the head, looking for grooves,pitting and particularly for cracking.

Slight pitting can usually be removed by grinding. More

serious pitting is removed by having the valve seatrecut at an engineering shop.

Clean all carbon and dirt from inside the inlet andexhaust ports, using a cup-type wire brush mounted inan electric-drill chuck. Protect your eyes with goggles.

Stubborn carbon particles can be removed by gently

scraping with a blunt screwdriver, followed by the wirebrush.

Checking valve guides

Check valve guides for wear by first refitting a valveinto its respective guide, then raising the valve slightlyoff its seat.

Try moving the valve head from side to side. If themovement at the valve head is more than 0.007 in. (0.2mm), the valve guide or the valve stem may beexcessively worn - check the manufacturer'sspecifications, given in a service manual, or consultyour local dealer.

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If there is too much movement, repeat the test using anew valve. If this has less movement, the old valvestem is worn and the valve must be replaced. If there isstill too much movement, the wear is in the guide andthe cylinder head should be taken to an engineeringshop for the replacement of all the guides.

If the guides are an integral part of the cylinder head,they can be reamed - opened out - to a larger size totake new valves with oversize valve stems. This workshould also be entrusted to an engineering shop.

Grinding and refitting the valves

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Generally valves should be ground, or 'lapped', intotheir 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 thincoating which must not be removed. When fittingcoated valves, use an old valve to grind the valve seat.

Smear clean engine oil on the valve stem, and attachthe valve head to the sucker on the end of the grindingtool.

Smear a thin film of grinding paste round thechamfered edge of the valve head and insert the valvefully into its guide.

Rotate the grinding tool back and forth between thepalms of the hands, pressing the tool and valve into itsseat at the same time.

After a minute of continuous grinding, raise the valveoff its seat, revolve it about 45 degrees, then continuethe grinding process for another minute.

Repeat the grinding procedure, altering the position ofthe valve periodically until both the valve-head flangeand the valve seat have an even, matt-grey

appearance, which indicates that the valve and seatare making good contact all the way round.

If slight pitting remains on the seat, use a coarsergrinding paste, followed by fine paste.

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When all the valves have been ground-in, remove themand place each in its order of removal.

Wash the cylinder head, combustion chambers andvalve ports thoroughly with paraffin, to remove alltraces 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 refitthe valves to their respective positions in the head.

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If there are oil seals, fit new ones over the valve stems,taking care to avoid damaging the seal lips. Always fitnew valve springs.

Place the new valve spring and spring cap in positionover the valve stem, noting that the close-coiled end ofthe spring is usually fitted next to the head.

Compress the valve spring with the compressor tooluntil the two split, tapered collets can be slipped intoposition between the spring cap and the valve stem.

Slowly release the compressor tool until both colletsare locking the spring cap and valve stem together.

Remove the compressor tool and repeat the valveinstallation procedure on the remaining valves, in theorder in which you removed them.

Cleaning the pistons and cylinder block

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Clean the piston crowns and cylinder-block face toremove any excess carbon and old head-gasketremains before replacing the cylinder head.

To prevent dirt or carbon particles entering the engineduring cleaning, seal oil and water passages in thecylinder-block face with pieces of clean, lint-free clothas necessary.

The cylinder bores, too, should be plugged with cleancloth to prevent dirt particles falling between the pistonsand cylinder walls.

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Use a scraper tool, such as the smooth side of ahacksaw blade, to carefully remove all traces of headgasket from the cylinder-block face. Take great care

not to scratch or damage the face.Rotate the crankshaft with a spanner or socket on thecrankshaft pulley bolt to bring each piston to the top ofits cylinder.

On engines with removable cylinders (wet-liners), holda block of wood down firmly over the top edge of all thecylinders as the crankshaft is turned.

This prevents the cylinder liners from being lifted as thepistons rise up the bores, and ensures that the coolantseals at the bottom of the cylinder liners are not broken.

When each piston is at TDC, use a soft scraper suchas a wooden block to carefully scrape carbon depositfrom its crown, leaving a small ring of carbon round the

outer edge adjacent to the cylinder wall.

Polish each piston crown with fine-grade emery cloth.

Clean all carbon and dirt from the cylinder bores andbolt holes, using either compressed air from a tyre footpump, or a vacuum cleaner.

Make certain there are no carbon particles lodged in

the bores.

Clean the block face, cylinder bores and piston crownswith a petrol or paraffin-moistened clean cloth, and thendry them.

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Be careful not to risk a fire - do not smoke, for example.

Smear a thin film of clean engine oil on each cylinder-bore wall and then remove the pieces of cloth from the

oil and water passages.