The following data were published by Patrick Knight in two articles in Stationary Engine magazine, the original information being compiled by Mr Duncan Masters. In the absence of any firm factory data the table may not be 100% accurate, but it is believed to be very close to what was actually used. Note that as industrial engines didn't appear until approximately the late 1930's then obviously you cannot have a Model 5 JAP engine dating to 1922!
J A Prestwich Engine Dating - Block 1 - 1920 to 1939
J A Prestwich Engine Dating - Block 2 - 1940 to 1959
J A Prestwich Engine Dating - Block 3 - Post 1959