For these reasons it is normally only possible to date Atco mowers to an approximate age within the known production period.
For example, many Atco Motor Mowers (The Atco Standard) from the 1920s have Villiers 147cc engines with "H" prefixes to the numbers.
Later, and into the 1930s, smaller Villiers "Midget" engines have CY or similar prefixes that also seem to be mower specific.
All Atco motor mowers produced during this period had either Villiers two-stroke or JAP four-stroke engines.
Both engine manufacturers numbered their engines and it is often possible to date a mower from these, bearing in mind that the original motor could have been replaced at a later date.
There were relatively few Atco models and it seems that the company was able to run its extensive service operations by simply knowing the type of mower and the cutting width.
From this could be determined the spare parts required and there was no need for any further complications.
Like many other manufacturers Atco ceased mower production during the Second World War to concentrate on other products.
The numbering and dating of JAP engines is covered by this list of JAP engine dates and this alternative list of JAP engine dates.
Dating Villiers engines is slightly more difficult for two reasons.
It is not easy to date Atco mowers made before 1939 with any precision.
The company does not appear to have numbered its mowers or used any systematic dating process.