Wolseley/Ruston Main Bearings
Stages in the production of a bearing in a nutshell -
When these bearings were in commercial production diecasting was used - this process uses an accurate metal mould and the molten alloy is forced in under pressure ensuring accurate conformity with the mould. In the home workshop diecasting equipment is not generally available, so gravity casting has to be resorted to. The description below is just an outline designed to provide an introduction to the subject for the curious and is not intended to be a comprehensive description of all aspects of the process. If you do plan to try this method of production, expect to have to experiment before an acceptable result is obtained, and expect the ultimate cost of a bearing to be somewhat greater than you might have expected if still obtainable commercially.
I plan to write a full article for Stationary Engine magazine when time permits.
Pattern : To start the process a pattern is required - an existing bearing will not be suitable for gravity cast items because although the mould may be accurate, shrinkage of the alloy on cooling will result in an undersize casting with poor surface finish. The pattern shown below is made from aluminium alloy. It needs to be oversized to allow the casting to be accurately machined to finished dimensions. Provision is made for a core mould so that the final casting is hollow.
The WD pattern
The mould is made in two parts from a high temperature silicone rubber as used by manufacturers of pewter figures. The pattern is set up half embedded in plasticine or similar modelling clay surrounded by a dam made from Lego bricks. Provision is made for accurate location of the mould halves by using location pegs which can also be made to provide suport for the mould when clamped together to prevent, or at least minimise distortion. The top half of the pattern is covered with silicone rubber solution which has been mixed with hardener. After 24hours the modelling clay can be removed carefully and the bottom half of the pattern cleaned up. The Lego brick dam is then increased in depth, the pattern and top half of the mould treated with mould release agent and the second half poured. Channels to provide a way in (and out) for the molten metal are now cut into the mould. The mould for the WD bearings used about 30 UK pounds worth of silicone rubber.
The photo below shows the pattern embedded in the bottom half of the mould.
Here the core piece (aluminium rod, tapered to facilitate removal from the casting) is assembled in one half of the mould prior to pouring the molten alloy -
Safety precautions need to be taken as the molten whitemetal will be at over 300 deg C - if this comes into contact with water, the liquid will vapourise in an instant showering the working area with molten metal - eye, hand and body protection is obligatory.
The whitemetal ingot is heated in a ladle until liquid and until the surface attains a blueish colouration. The surface of the molten metal is scraped with a flat stick to remove the dross (oxidation products) before quickly pouring it into the mould which is clamped together containing the core. Metal is poured into the feeder until it emerges from the vent - these headers provide material to be withdrawn into the mould during contraction on cooling and prevents blow holes.
A good cast -
The speed of pouring is critical to a good result - if poured too slowly the metal solidifies before the mould is full and blow holes can result as shown below -
Incomplete filling of the mould
Blow hole under the rim of the flange which would be a weak spot
Machining : The fettled casting can be machined to produce the final bearing in stages as shown below - rough casting on the right, finished article on the left -
The alloy I have used is approximately to BS3332A (89% tin, 7.5% antimony, 3.5% copper) which should give longer service life than the original lead-based Wolseley bearings. My alloy was obtained from a former tin-miner still working with the metal close to Geevor mine in Cornwall.
Alloys with even better characteristics than the BS alloys can be obtained (eg from Hoyt Darchem Ltd in the UK) - these should be used for highly stressed components such as big end bearings which have to cope with shock loads as well as rotational loads.
Expect tp pay 10 to 20 UK pounds per kilo for bearing alloy (dependent on grade and amount purchased).
I also made a bronze bearing for my own WD2 - a blank was made by hard soldering together two pieces of hollow leaded bronze to make the basic top hat shape -
This was machined to the same dimensions as the whitemetal casting to produce the final broze bearing, compared here with a Wolseley whitemetal original -
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