Rebuilding V8 Cylinder Heads.

This section explains how to rebuild the Rover V8 Cylinder heads

Removing the heads

Remove the rocker cover and discard the cork or rubber gasket. Rinse thoroughly in paraffin to remove the grot and oil. Clean or replace the breather/flame trap screwed into front of the left hand cover. Leave to dry.

Rockers

The rocker shafts do not need to be removed to lift the heads but it's easier to get the rocker shaft bolts undone in situ. Remove the rocker shaft, starting with the centre bolt and working outwards alternately. Put on one side for examination later.

Remove Pushrods

Lift out the pushrods, retaining the order and direction of them as the ends are similiar but wear differently. Examine the ends of each one. The should be shiny, domed and with a small flat on the top of the dome. Any pits, steps or points in the dome indicate failure and possible damage to either the follower or the rocker. Usually if one is bad they all are. If the follower ends seem ok then the followers may be serviceable depending on the state of the camshaft. If the rocker end is damaged or severely worn then the rocker(s) should be renewed.

Head Bolts

The heads are held down to the block by 15 large bolts (10 on late engines) which must be removed or refitted in stages and in order. The rocker cover hides 5 of them when fitted. The Haynes manual has a good picture of the order and description of the sequence. Once all the bolts are removed, take a soft faced mallet and tap around the exhaust and inlet areas to loosen the head. They usually lift off very easily but take care not to slide it sideways once it lifts as there are dowels in the block which may damage the sealing face of the head.

Inspection

Wash all the parts in paraffin/white spirit/Jizer etc to remove the loose oil and grot. The parts will usually still have a gritty/tarry black deposit on them unless they are very low mileage.

Inspect Head gasket

Examine the gasket and the block and head faces for signs of leakage, this usually shows a as a brown or blackened area on one side of one or more cylinders, usually into the valley side of the block. Also check for corrosion around the water way at each end of the block and head. Sometimes a kind of thermal damage occurs where the gasket wears against the head or block, leaving a shallow circular groove in the surface. Any damage, burns or corrosion on the surfaces may require machining of block and/or heads.

Inspect Valves

Examine the valves, any signs of mushrooming or belling of the top of the stem mean the valve is finished and must be replaced. Shallow depressions are not unusual but are worn and still serviceable depending on what else you find. Check for broken valve springs and any apparent mechanical damage. Early heads have double springs so check inside the coils of the outer springs for broken inner springs. If the valves appear to be in good condition and oil consumption if any was due to worn rings and bores then the valves should still be serviceable if you aren't planning a full rebuild. If this is the case then don't dismantle the valves, just clean the gasket faces, oil the valve stems and store the head in a clean plastic bag for reuse. If you plan to renew valves or springs then you will need a valve spring compressor tool. If a valve needs replacement or the seats and guides are worn or damaged then a machine shop will be necessary to fit inserts or new guides and ream them and replace or recut the seats.

Richard and Frida Turner are good at this work. If the valve is being replaced due to belling, burnout or cracking it may be possible to get away with less. Belled stem ends must be ground until the can be withdrawn with damaging the guide. There is a standard procedure for lapping new valves onto old seats, it is important that the fit in the guide is correct. A tight fit is not good and a side clearance of at least 2 thousands of an inch over the entire length of the guide is essential.

Inspect Rockers

Return to the rocker shaft and examine the rockers. The rocker is alloy with inserts for the heels and toes. The toes press on the valve stem and usually wear normally with a shallow circular depression. If there is damage or pits here then the rocker is scrap. The heel has the end of the pushrod inside it. Occasionally the cup gets worn and/or cracked and can even collapse. Scrap if so. Often the small lubrication hole blocks up. These need to be cleared. If the rocker cannot be slid sideways at all on the shaft, then the shaft is probably worn with a step and should be renewed in which case it's best to renew the whole assembly. You can reuse the springs, pillars and end washers but renew the split pin. The rocker pillars are often difficult to remove. I find that a solution of caustic soda and washing powder will shift enough of the grot to get it apart without too much trouble unless someone has crushed the pillars by overtightening the bolts, in which case you will need new pillars too.

Do not leave the assembly in caustic soda for more than a few minutes as the alloy will corrode. Rebuilding is simple butlubricate everything copiusly, noting that the rockers are handed and need to be assembled so the valve stem sits on the centre of the steel pad in the heel. The correct torque for the bolts in the rocker pillars (pedestals) is important. Generally I have to renew the complete rocker assembly except the pillars, sometimes renew the valve springs and very lightly lap the valves to the seat and I find that worn guides are rarely an issue on these heads. Later heads have a valve stem seal which can be retrofitted to all heads to reduce oil passing down the valve guides. This works very well on slightly worn guides.

Cleaning

Steel parts like valves and bolts can be left for weeks in Caustic soda to clean them and even the hardest coke will come off exhaust valves this way. Aluminium alloy will corrode once the oil film is broken down so they should be washed and agitated and brushed to remove the grot then thoroughly rinsed with very hot water, I find a jet wash usually gets them very clean once the soda has had a go. Dry and coat with oil as steel and alloy parts can corrode instantly when properly cleaned.

Lifter Preload

If you have fitted a mild performance cam of the type which do not require additional headwork, then you are strongly advised to check the preload on the cam followers as the base circle on the camshaft is likely to be different. This is rather easy and requires only a piece of welding rod with the last 5mm bent at 90 degrees and squashed to 30-40 thousands of an inch diameter as a gauge. With the heads and rocker gear fitted and torqued, rotate the engine to TDC on No.1 cylinder. Both inlet and exhaust valve should be closed and it should be possible to insert the gauge between the pushrod seat in the follower and the circlip in the top of the follower. Record the clearance and do this for each follower, making sure the follower being measured is on the opposite side to the lobe. The acceptable range is 20-60 thou for standard engines and purists should aim for 40. If any values are larger than this then the rocker pedestals will need to be shimmed by an amount sufficient to keep all of the clearances in the acceptable range. Use the same size shim under each pedestal otherwise a broken rocker shaft will result and make sure the oilway hole lines up with the drilling in the cylinder head. If the values are less than 20 thou, in all probability you are using worn rocker gear and wasting your time or your assembly is wrong. Values too large require shims under the rocker pedestals, values too small require machining of the rocker pedestal bases by the required amount. This is a very unusual condition with new components and everything else should be checked before cutting metal. The rockers have a ratio of 1.6, which means that if you need to correct a preload of 50 thou down to 30 thou, you will need shims which are (50-30) x 1.6 = 30 thou thick. Packs of shims are available from Real Steel and can be made from shim stock if required. If you have had the heads and/or block machined and/or have moved from a composite to a tin head gasket and have fitted a performance cam, there is a small possibility that the preload on the followers will be excessive to the point that fully tightening the rocker shaft bolts will overstress a pushrod or rocker arm. If this is so, check the preload while progressively bolting down the rocker shafts and shim as appropriate before applying final torque. Some (very few) aftermarket cams specify different preload settings so check carefully what the preload should be.

Max Valve Lift

Maximum valve lift that a standard engine can take is 0.44". Any more than this requires modification of the valve guides as a minimum. If using a cam which approaches this value then a dummy build using test springs is strongly recommended to ensure valve guide to spring retainer clearance of at least 0.1" is present. Some engineering shops can machine the guides in situ, which is preferable to pressing them out and machining them or fitting shorter guides.

Piston Clearance

Some long duration, high lift cams also put the inlet valve face very near the piston crown at the end of the exhaust stroke and this should be checked too. Useful to have a lump of Plasticine to stick to the top of the piston when checking this. A minimum of 1.5mm (0.060") clearance is necessary. Using test springs rather than valve springs will make it easy to rotate the engine and avoid any chance of damage to valves, pistons or rotating assemblies.