The Daimler V8 engine does not utilise a valve stem oil seal as standard. A valve stem oil seal grips around the valve stem whilst allowing the valve to open and close smoothly. The seal stops engine oil travelling down the valve and into the combustion chamber where it is burnt. The puff of blue smoke on start up or overrun is is the result of this problem and is a common complaint with owners. As the valve guide wears, this problem is amplified.
The standard valve guide (Fig.47(below)) is a hard ductile cast iron (SG) smooth wall construction which requires a clearance of approx 0.002” / 0.003” to allow the valve stem to move correctly. As the valve guide and valve stem wears, this clearance is unavoidably increased which allows oil to pass; with the rocker action causing most of the valve guide wear.
Considering this information, there are two problems to solve:
1- excess valve stem clearance
2- unrestricted oil passage through the guide into the cylinder.
The common denominator here is the guide and this is where the modification takes place. The original valve guide was made from SG Iron, an advanced material at the time which is very hard and difficult to machine. Therefore we need to remove the guide and replace it with a standard grey cast iron guide (Fig.48(left)) which can be machined easily.
Prior to fitting the guide, the top is machined to accept a modern valve stem oil seal with a garter spring, see Fig 49(below).
Once the outside machining is complete the new guides are pressed into the cylinder head up to a shouldered stop. At this stage and using this type of valve guide we have actually downgraded (!!) the specification as the new cast material is nowhere near as good as the original SG Iron material fitted as an OE item.
Hence this is where the fitting of genuine K-Line bronze bullet guide liners (Fig.50(left) comes into play; it should also be noted that there are equivalent bronze guide liners but their quality is poor. Thus you need to ensure that ONLY genuine K-Line inserts are being used.
The standard grey cast iron is simply a holder / host and its wear characteristics are now redundant. This new modified valve guide with the bronze lining and valve stem oil seal now exceeds the OE specification and is suitable for unleaded fuel. The bronze liner material has anti-seizing properties and higher rate of thermal conductivity, as well as a lower coefficient of friction.
With these characteristics it is now possible to run a far tighter valve stem to guide clearance which assists reducing the amount of oil that can pass into the combustion chamber. Fig.51(right) shows a cut-away view of the new valve guide with the K-Line bronze liner. Note the interrupted spiral on the inside which helps arrest any oil being passed through into the combustion chamber.
Fig.52(left) shows the guide with the valve stem oil seal in place. At this stage, the original specification has now been exceeded in both material and oil control properties.
Fig.53(right) shows the complete assembly – that being: the modified valve guide with K-Line bronze liner, valve stem oil seal and new valve. Beautiful !!
Valve Seats and Springs:
Once the valve guides have been modified the valve seat geometry must be restored so that it is concentric with the guide bore. This CANNOT be achieved with the use of lapping sticks and carborundum paste (!!) they MUST be re-cut. Any damaged, excessively worn or valve seats which have been cut too deep will hinder geometry, air flow plus performance and therefore must be replaced.
The old valve seats are removed by cutting them out (Fig.54(below)) to prevent damage to the aluminium.
A Hi-Chrome sintered metal seat insert, as used by “J&E Engineering Services” is fitted (Fig.55(below)) which is suitable for unleaded fuel. The seats are fitted with an interference fit of around 0.004” and secured with adhesive.
The seats are then cut to the correct depth (Fig.56(below)) including seat angle arrangement to ensure perfect seat sealing. The valve guide is used as a datum for this operation and ensures concentricity.
When cutting valve seats and replacing valves, it is very important to keep in mind the relationship between this operation and the valve spring. Seats cut too deep or badly worn valves, will cause the valve spring seating pressure to be relieved; this in turn can cause valve spring bounce which may lead to valve or valve seat failure. A seat which is not cut deep enough can result in a spring binding situation, which will lead to valve / guide failure – 100% guaranteed. Therefore it is critical to observe the valve spring fitted height or installed height to ensure seating pressures are maintained and coil binding is avoided.
Fig.57(below) clearly shows how excessive valve seat cutting will directly affect valve spring pressures.
Fig.58(above) shows a tool for measuring valve spring installed height and Fig.59(below) shows the machine checking valve spring pressure at seating and full lift situations. By doing this, it ensures that the spring will not bounce and that coil binding is avoided.
Valve spring shims and platforms (Fig.60(below)) can be used to correct spring pressure and balance springs. These generally come in three different thicknesses: 0.015” / 0.030” / 0.060” and are used to compensate for valve seat cutting.
The following is of interest:
1- outer valve spring installed height = 1.31”
2- inner valve spring installed height = 1.23”
3- valve seating spring pressure – 55lb/in
Part 6, the concluding episode, of this series will cover spark plug tube sealing; focusing upon the recently designed modified oil seal kit, which has eliminated that well known “oil in your tubes” problem along with some other items which may be of interest.