The present invention relates to the assembly of poppet valves in an internal combustion engine, and seeks to facilitate automation of valve assembly.

A poppet valve as used in the cylinder head of an engine has a valve stem which passes through a valve guide in the cylinder head and its protruding end is surrounded by a valve spring which acts on the stem in a direction to close the valve. A spring retainer is secured to the valve stem by means of tapered valve collets which engage a circumferential groove in the valve stem and the valve spring acts between the spring retainer and a spring seat which rests on the cylinder head. The spring seat is required because the material of the cylinder head would be damaged by the sharp edge of the valve spring and at least a washer is required between these two surfaces.

It is further required to provide, at a suitable place, an oil seal to prevent oil from running down the valve stem into the ports. This oil seal may be in the form of a cap fitting over the end of the valve guide though it has also been proposed to include the oil seal in the spring seat.

The assembly of a spring on a valve involves first fitting the oil seal to the valve stem, then placing the spring seat, spring and retainer, in that order, over the valve stem. Next the spring is compressed by pushing the retainer below the level of the groove in the valve stem, the valve collets are placed in the groove and finally the spring is released. Upon release of the retainer, the valve collets are held captive in the groove by the retainer and they in turn prevent the retainer from sliding up the. length of the valve stem.

Because of the large number of individual parts mvoiveα and because of the complexity in handling some of these parts, the task of assembly of a valve spring was hitherto considered too complex to automate and has instead been carried out manually. This, of course, adds to the cost of manufacture and the present invention seeks to mitigate the foregoing problem.

In accordance with a first aspect of the present invention, there is provided a method of assembling a valve which includes the steps of securing a spring seat, a spring and a spring retainer to one another to form a sub-assembly, and fitting the sub-assembly as a single component over the valve stem.

The components of the sub-assembly may be secured to one another by means of an adhesive or by virtue of their form being a locking fit in one another. For example, the retainer and the valve seat may have cylindrical extensions resiliently engaged by the coils of the spring and capable of holding the components together for later assembly without the use of an adhesive.

Because all three components are held together, they reduce the number of parts that have to be fed to and manipulated by an automated assembly line or robot. Conveniently, a stack of such sub-assemblies may be contained in a cylindrical magazine and in a single operation a sub-assembly can be removed from the magazine and fitted over the valve stem.

It is preferred that the spring seat be provided with an oil seal sealing against the valve stem so that the only operation required after the fitting of the sub-assembly over the valve, stem is the mounting of the valve collets.

In accordance with a second aspect of the invention, there is provided a sub-assembly for facilitating automated assembly of valve springs onto poppet valves, the sub- assembly comprising a valve spring secured at one end to a spring seat and at the other end to a spring retainer, whereby all three components may be mounted simultaneously over the stem of a poppet valve.

Preferably, the spring seat is provided with a seal for sealing against the stem of the poppet valve.

In a further aspect of the invention, there is provided a magazine comprising a plurality of sub-assemblies as set out above stacked vertically one above the other whereby to facilitate the supply of the sub-assemblies to an automated assembly line.

The spring seats in conventional engines are hat shaped and are centred on the valve step by being fitted over a boss surrounding the valve stem and protruding from the surface of the cylinder head. The presence of such a boss serves the useful purpose of preventing the oil provided for lubricating the valves from running down the stem into the combustion chambers but has the disadvantage of interfering with the machining of the cylinder head, it being difficult to work around the bosses.

In accordance with a still further aspect of the invention, there is provided a spring seat adapted to fit around the stem of a poppet valve in a cylinder head in between the cylinder head and a valve spring acting on the poppet valve, the cylinder head being provided with a recess surrounding the valve stem for receiving the spring seat, wherein the spring seat is provided with two oil seals, the first operative to seal against the stem of the poppet valve and the second against the surface of the cylinder head.

Preferably, the spring seat is hat shaped and has an axiax seal resting on the surface of the cylinder head and a radial seal for engaging the surface of the valve stem. The cylindrical portion of the seat now acts to centre the valve spring and the force of the spring urges the axial seal against the cylinder head.

Because of the provision of two seals on the spring seat, there is no need for a boss on the cylinder head and this simplifies manufacture without creating any problems in containing the oil in the valve chamber.

The invention will now be described further, by way of example, with reference to the accompanying drawing which is a section through a sub-assembly of a spring seat, a valve spring and a retainer placed above a cylinder head.

In the drawing, a cylinder head 10 is provided with a flat upper surface 12 and with a valve guide 14. A recess 16 is formed in the cylinder head 10 surrounding the upper end of the valve guide dimensioned to receive a spring seat 18.

The spring seat 18 forms part of a sub-assembly of three components which are secured to one another by means of an adhesive. The other two components are a spring 20 and a spring retainer 22 which is engaged by the valve collets in the usual manner when the valve is fully assembled and acts to transfer the force of the spring to the valve stem. The poppet valve and the valve collets are not shown in the drawing.

The spring seat 18 is hat shaped having a rim 24 against which the spring 20 rests. The lower surface of the rim 24 is formed with- an elasto eric oil seal 26 which in use is held in sealing contact with the surface of the cylinder head by the force of the valve spring 20.

The top of the spring seat 18 has a central aperxure through which the valve stem passes and in which there is provided a second oil seal 28. The design of the latter seal may be conventional and is shown as fitted with a resilient collar 30 which urges the inwardly projecting lip of the seal 28 into radial contact with the surface of the valve stem.

The spring seat has been described as having two separate seals and this is illustrated on the left half of the section shown in the drawing. It is however alternatively possible for a single elastomeric layer adhering to the metal of the spring seat and this is shown to the right in the drawing.

In the assembly of cylinder heads in an automated line, sub-assemblies of springs, as illustrated, are provided in a magazine to an assembly robot which removes sub- assemblies from the magazine, one at a time, and places them over the valve stems in the cylinder head. The springs are then compressed by pressing down on the retainers 22 and the valve collets are placed about the grooves in the upper ends of the valve stems before releasing the pressure on the spring retainers 22.

It should be mentioned that in the prior art, valve springs have not been packaged in magazines and tended to become entangled with one another making unpacking alone a time consuming task. When assembled into sub-assemblies as proposed in the present invention, the springs are prevented from becoming entangled even when not packed in magazines ready for dispensing one at a time.

It can thus be seen that the invention facilitates automation of assembly and also enables manufacturing costs to be reduced by simplifying the machining of the cylinder head.