Learning Resources

Bentley Engine

Bentley Engine

1930s Rolls-Royce/Bentley Small Horsepower Engine Cutaway

Cutaway:   by R. Pierce Reid at Vintage Garage in Stowe, Vermont in 2012

The engine is an amalgam of period parts built around an engine that threw a connecting rod through the aluminum crankcase.  Sharp eyed viewers will see the ‘ragged’ hole created by the thrown rod.  The Small Horsepower range of Rolls-Royce and ‘Derby’ Bentley engines first appeared in 1923 in the 20HP series of Rolls-Royce cars. The engine grew between its introduction and its replacement (in 1938) in displacement and output.  Additional changed increase size of crankshaft, bearings, etc. as power increased.  In 1933, the engine was modified with a cross-flow head and used for new Derby Bentley engines, significantly increasing power.  The cutaway is intended to showcase both the complexity of the engine, but also things that ‘go wrong.’  Viewers can see how lime and corrosion build up in the block to displace water, insulate running surfaces and cause overheating problems – the root cause of the rod failure on this engine.

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