Left and Right Engineering

AEC made a proper engineering adaption of their right hand drive chassis to suit the left hand cab. Without this, access to parts such as injectors and the fuel pump would be restricted in left hand versions, requiring the engine to be removed for otherwise quick repair tasks. The financial investment in creating castings for both variants would have been large. The quantity of handed components required to create two versions of the half cab bus was much higher than say a left or right hand drive lorry or car. However for most of the world’s population the rule of the road is to drive on the right, requiring the left hand chassis. 
The decision to build both variants demonstrates AEC had ambitious plans to make significant sales volumes worldwide. In late 1940s Britain this was a realistic aim, when other countries had hardly begun to recover from the Second World War manufacturing opportunities for export from the UK were huge and were encouraged by the British Government to generate foreign exchange. By 1947 AEC had created fully reworked left hand drive variant of their right hand drive Regal and Regent half cab bus chassis. Production required a mixture of standard parts suited for both left and right hand drive versions and unique parts for one or other version.  
The chassis and mechanical parts of our bus are intriguing. Handed versions of many components including the engine, radiator, steering box, gear lever turret, gearbox, and rear axle were made to suit the left hand version. The engine is the most complex adaption, the block, crankcase, sump, fuel pump casing, injector pipes and water pump are handed. The engine crankshaft, cylinder heads, pistons, injectors, flywheel are interchangeable. 
Luckily, the wearing mechanical components suit either version, but the casings for most are handed. This means components for repair can be sourced from stock held for left or right hand versions. Only a catastrophic failure, such as ‘a leg out of bed’ (connecting rod coming adrift and smashing the sump) will need a handed part replaced. 
In more recent times the DAF engines fitted to London Routemasters were wrongly handed making repair access difficult, time consuming and therefore more costly.