07-05-2020, 11:14 AM
The late Ray Walker who spent most of his working life repairing and restoring Sevens told me that two bearing cranks usually go at somewhere around 28 or 56 mph. This suggests that there is a resonant frequency, and maintaining the relevant engine revs for too long will encourage failure. Another learned metallurgist friend and Austin Seven enthusiast confirmed that any piece of steel is likely to break after a particular number (usually very high) of bending actions has been applied to it. Combining these theories suggests that all shafts will fail in the end. Modern techniques such as nitriding are proved to extend the life, but I presume there are still limits as to how long a component will last.
Robert Leigh
Robert Leigh