John Cogdon

From the MEWS archive, a non dead centre engine by John Cogdon. Non-dead-centre engines were designed solve the problem of engine stopping on dead centre.The dead centre of a piston engine with cranks is when the piston is at the exact top or bottom of the stroke and so the piston cannot exert any torque on the crankshaft. If a steam engine stops on dead centre, it will be unable to restart from that position. Obviously this is not a problem for I/C engines which have to be cranked to start.

Several solutions were applied. Simplest is to try not to stop in this position; the crudest to apply a strong arm with a crowbar to turn the engine over a little. Small steam barring engines were also used to move the engine away from dead centre before starting. If the engine has multiple cylinders, most geometries for these are arranged so that all cylinders are never at dead centre together and so one may always be used for starting.