The AP, or Agricultural Paraffin engine was introduced in the early 1920's soon after Richard Hornsby & Sons merged with Ruston Proctor & Co just after the First World War. Production continued until the the early 1940's, so this engine represents the middle of the production run. By 1930 the carburettor had been modified and low tension magnetos had been replaced by high tension units like the Wico EK, the brass box seen here just below the hopper which is operated from an excentric on the cam shaft. This particular engine is slightly unusual in that it is fitted with a mechanical lubricator for the cylinder and big end. Normally on these AP engines, and even the industrial engines (classes IP and OK) of this size, lubrication was from drip oilers, however this must have been a factory fitted option right from the outset as there is a special pad cast into the main engine bed casting for the stud which secures the lubricator, and this is not present on drip libricated engines.

The major job required to make the engine run was the manufacture of a new set of main bearings since the original whitemetal bearings had suffered poor lubrication and they had run (partly melted). After experimenting with gravity casting replacement half bearings in whitemetal (a tin/antimony/copper alloy) and not achieving the required accuracy, new bearings have been made from a piece of heavy cast bronze tube to get the engine going, which it will as soon as it stops raining long enough for me to get the tarpaulin off ! I may have another go at authentic whitemetal bearings later - this time I will cast an oversize tube and aim to split it and machine back to accurate dimensions just as I did with the bronze.

Eventually it should look like this engine just a month or two older than # 139113 (seen at the Lincoln Rally, August 1998).....

Engine Data Table

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